particle_system.c

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/*
 * ***** BEGIN GPL LICENSE BLOCK *****
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * The Original Code is Copyright (C) 2007 by Janne Karhu.
 * All rights reserved.
 *
 * The Original Code is: all of this file.
 *
 * Contributor(s): Raul Fernandez Hernandez (Farsthary), Stephen Swhitehorn.
 *
 * Adaptive time step
 * Copyright 2011 AutoCRC
 *
 * ***** END GPL LICENSE BLOCK *****
 */

#include <stddef.h>

#include <stdlib.h>
#include <math.h>
#include <string.h>

#ifdef _OPENMP
#include <omp.h>
#endif

#include "MEM_guardedalloc.h"

#include "DNA_anim_types.h"
#include "DNA_boid_types.h"
#include "DNA_particle_types.h"
#include "DNA_mesh_types.h"
#include "DNA_meshdata_types.h"
#include "DNA_modifier_types.h"
#include "DNA_object_force.h"
#include "DNA_object_types.h"
#include "DNA_material_types.h"
#include "DNA_curve_types.h"
#include "DNA_group_types.h"
#include "DNA_scene_types.h"
#include "DNA_texture_types.h"
#include "DNA_ipo_types.h" // XXX old animation system stuff... to be removed!
#include "DNA_listBase.h"

#include "BLI_edgehash.h"
#include "BLI_rand.h"
#include "BLI_jitter.h"
#include "BLI_math.h"
#include "BLI_blenlib.h"
#include "BLI_kdtree.h"
#include "BLI_kdopbvh.h"
#include "BLI_threads.h"
#include "BLI_utildefines.h"
#include "BLI_linklist.h"

#include "BKE_main.h"
#include "BKE_animsys.h"
#include "BKE_boids.h"
#include "BKE_cdderivedmesh.h"
#include "BKE_collision.h"
#include "BKE_displist.h"
#include "BKE_effect.h"
#include "BKE_particle.h"
#include "BKE_global.h"

#include "BKE_DerivedMesh.h"
#include "BKE_object.h"
#include "BKE_material.h"
#include "BKE_cloth.h"
#include "BKE_depsgraph.h"
#include "BKE_lattice.h"
#include "BKE_pointcache.h"
#include "BKE_mesh.h"
#include "BKE_modifier.h"
#include "BKE_scene.h"
#include "BKE_bvhutils.h"

#include "PIL_time.h"

#include "RE_shader_ext.h"

/* fluid sim particle import */
#ifdef WITH_MOD_FLUID
#include "DNA_object_fluidsim.h"
#include "LBM_fluidsim.h"
#include <zlib.h>
#include <string.h>

#endif // WITH_MOD_FLUID

/************************************************/
/*          Reacting to system events           */
/************************************************/

static int particles_are_dynamic(ParticleSystem *psys)
{
    if(psys->pointcache->flag & PTCACHE_BAKED)
        return 0;

    if(psys->part->type == PART_HAIR)
        return psys->flag & PSYS_HAIR_DYNAMICS;
    else
        return ELEM3(psys->part->phystype, PART_PHYS_NEWTON, PART_PHYS_BOIDS, PART_PHYS_FLUID);
}

static int psys_get_current_display_percentage(ParticleSystem *psys)
{
    ParticleSettings *part=psys->part;

    if((psys->renderdata && !particles_are_dynamic(psys)) /* non-dynamic particles can be rendered fully */
        || (part->child_nbr && part->childtype) /* display percentage applies to children */
        || (psys->pointcache->flag & PTCACHE_BAKING)) /* baking is always done with full amount */
        return 100;

    return psys->part->disp;
}

static int tot_particles(ParticleSystem *psys, PTCacheID *pid)
{
    if(pid && psys->pointcache->flag & PTCACHE_EXTERNAL)
        return pid->cache->totpoint;
    else if(psys->part->distr == PART_DISTR_GRID && psys->part->from != PART_FROM_VERT)
        return psys->part->grid_res * psys->part->grid_res * psys->part->grid_res - psys->totunexist;
    else
        return psys->part->totpart - psys->totunexist;
}

void psys_reset(ParticleSystem *psys, int mode)
{
    PARTICLE_P;

    if(ELEM(mode, PSYS_RESET_ALL, PSYS_RESET_DEPSGRAPH)) {
        if(mode == PSYS_RESET_ALL || !(psys->flag & PSYS_EDITED)) {
            /* don't free if not absolutely necessary */
            if(psys->totpart != tot_particles(psys, NULL)) {
                psys_free_particles(psys);
                psys->totpart= 0;
            }

            psys->totkeyed= 0;
            psys->flag &= ~(PSYS_HAIR_DONE|PSYS_KEYED);

            if(psys->edit && psys->free_edit) {
                psys->free_edit(psys->edit);
                psys->edit = NULL;
                psys->free_edit = NULL;
            }
        }
    }
    else if(mode == PSYS_RESET_CACHE_MISS) {
        /* set all particles to be skipped */
        LOOP_PARTICLES
            pa->flag |= PARS_NO_DISP;
    }

    /* reset children */
    if(psys->child) {
        MEM_freeN(psys->child);
        psys->child= NULL;
    }

    psys->totchild= 0;

    /* reset path cache */
    psys_free_path_cache(psys, psys->edit);

    /* reset point cache */
    BKE_ptcache_invalidate(psys->pointcache);

    if(psys->fluid_springs) {
        MEM_freeN(psys->fluid_springs);
        psys->fluid_springs = NULL;
    }

    psys->tot_fluidsprings = psys->alloc_fluidsprings = 0;
}

static void realloc_particles(ParticleSimulationData *sim, int new_totpart)
{
    ParticleSystem *psys = sim->psys;
    ParticleSettings *part = psys->part;
    ParticleData *newpars = NULL;
    BoidParticle *newboids = NULL;
    PARTICLE_P;
    int totpart, totsaved = 0;

    if(new_totpart<0) {
        if(part->distr==PART_DISTR_GRID  && part->from != PART_FROM_VERT) {
            totpart= part->grid_res;
            totpart*=totpart*totpart;
        }
        else
            totpart=part->totpart;
    }
    else
        totpart=new_totpart;

    if(totpart != psys->totpart) {
        if(psys->edit && psys->free_edit) {
            psys->free_edit(psys->edit);
            psys->edit = NULL;
            psys->free_edit = NULL;
        }

        if(totpart) {
            newpars= MEM_callocN(totpart*sizeof(ParticleData), "particles");
            if(newpars == NULL)
                return;

            if(psys->part->phystype == PART_PHYS_BOIDS) {
                newboids= MEM_callocN(totpart*sizeof(BoidParticle), "boid particles");

                if(newboids == NULL) {
                     /* allocation error! */
                    if(newpars)
                        MEM_freeN(newpars);
                    return;
                }
            }
        }
    
        if(psys->particles) {
            totsaved=MIN2(psys->totpart,totpart);
            /*save old pars*/
            if(totsaved) {
                memcpy(newpars,psys->particles,totsaved*sizeof(ParticleData));

                if(psys->particles->boid)
                    memcpy(newboids, psys->particles->boid, totsaved*sizeof(BoidParticle));
            }

            if(psys->particles->keys)
                MEM_freeN(psys->particles->keys);

            if(psys->particles->boid)
                MEM_freeN(psys->particles->boid);

            for(p=0, pa=newpars; p<totsaved; p++, pa++) {
                if(pa->keys) {
                    pa->keys= NULL;
                    pa->totkey= 0;
                }
            }

            for(p=totsaved, pa=psys->particles+totsaved; p<psys->totpart; p++, pa++)
                if(pa->hair) MEM_freeN(pa->hair);

            MEM_freeN(psys->particles);
            psys_free_pdd(psys);
        }
        
        psys->particles=newpars;
        psys->totpart=totpart;

        if(newboids) {
            LOOP_PARTICLES
                pa->boid = newboids++;
        }
    }

    if(psys->child) {
        MEM_freeN(psys->child);
        psys->child=NULL;
        psys->totchild=0;
    }
}

static int get_psys_child_number(struct Scene *scene, ParticleSystem *psys)
{
    int nbr;

    if(!psys->part->childtype)
        return 0;

    if(psys->renderdata)
        nbr= psys->part->ren_child_nbr;
    else
        nbr= psys->part->child_nbr;

    return get_render_child_particle_number(&scene->r, nbr);
}

static int get_psys_tot_child(struct Scene *scene, ParticleSystem *psys)
{
    return psys->totpart*get_psys_child_number(scene, psys);
}

static void alloc_child_particles(ParticleSystem *psys, int tot)
{
    if(psys->child){
        /* only re-allocate if we have to */
        if(psys->part->childtype && psys->totchild == tot) {
            memset(psys->child, 0, tot*sizeof(ChildParticle));
            return;
        }

        MEM_freeN(psys->child);
        psys->child=NULL;
        psys->totchild=0;
    }

    if(psys->part->childtype) {
        psys->totchild= tot;
        if(psys->totchild)
            psys->child= MEM_callocN(psys->totchild*sizeof(ChildParticle), "child_particles");
    }
}

/************************************************/
/*          Distribution                        */
/************************************************/

void psys_calc_dmcache(Object *ob, DerivedMesh *dm, ParticleSystem *psys)
{
    /* use for building derived mesh mapping info:

       node: the allocated links - total derived mesh element count 
       nodearray: the array of nodes aligned with the base mesh's elements, so
                  each original elements can reference its derived elements
    */
    Mesh *me= (Mesh*)ob->data;
    PARTICLE_P;
    
    /* CACHE LOCATIONS */
    if(!dm->deformedOnly) {
        /* Will use later to speed up subsurf/derivedmesh */
        LinkNode *node, *nodedmelem, **nodearray;
        int totdmelem, totelem, i, *origindex;

        if(psys->part->from == PART_FROM_VERT) {
            totdmelem= dm->getNumVerts(dm);
            totelem= me->totvert;
            origindex= dm->getVertDataArray(dm, CD_ORIGINDEX);
        }
        else { /* FROM_FACE/FROM_VOLUME */
            totdmelem= dm->getNumFaces(dm);
            totelem= me->totface;
            origindex= dm->getFaceDataArray(dm, CD_ORIGINDEX);
        }
    
        nodedmelem= MEM_callocN(sizeof(LinkNode)*totdmelem, "psys node elems");
        nodearray= MEM_callocN(sizeof(LinkNode *)*totelem, "psys node array");
        
        for(i=0, node=nodedmelem; i<totdmelem; i++, origindex++, node++) {
            node->link= SET_INT_IN_POINTER(i);

            if(*origindex != -1) {
                if(nodearray[*origindex]) {
                    /* prepend */
                    node->next = nodearray[*origindex];
                    nodearray[*origindex]= node;
                }
                else
                    nodearray[*origindex]= node;
            }
        }
        
        /* cache the verts/faces! */
        LOOP_PARTICLES {
            if(pa->num < 0) {
                pa->num_dmcache = -1;
                continue;
            }

            if(psys->part->from == PART_FROM_VERT) {
                if(nodearray[pa->num])
                    pa->num_dmcache= GET_INT_FROM_POINTER(nodearray[pa->num]->link);
            }
            else { /* FROM_FACE/FROM_VOLUME */
                /* Note that sometimes the pa->num is over the nodearray size, this is bad, maybe there is a better place to fix this,
                 * but for now passing NULL is OK. every face will be searched for the particle so its slower - Campbell */
                pa->num_dmcache= psys_particle_dm_face_lookup(ob, dm, pa->num, pa->fuv, pa->num < totelem ? nodearray[pa->num] : NULL);
            }
        }

        MEM_freeN(nodearray);
        MEM_freeN(nodedmelem);
    }
    else {
        /* TODO PARTICLE, make the following line unnecessary, each function
         * should know to use the num or num_dmcache, set the num_dmcache to
         * an invalid value, just incase */
        
        LOOP_PARTICLES
            pa->num_dmcache = -1;
    }
}

static void distribute_simple_children(Scene *scene, Object *ob, DerivedMesh *finaldm, ParticleSystem *psys)
{
    ChildParticle *cpa = NULL;
    int i, p;
    int child_nbr= get_psys_child_number(scene, psys);
    int totpart= get_psys_tot_child(scene, psys);

    alloc_child_particles(psys, totpart);

    cpa = psys->child;
    for(i=0; i<child_nbr; i++){
        for(p=0; p<psys->totpart; p++,cpa++){
            float length=2.0;
            cpa->parent=p;
                    
            /* create even spherical distribution inside unit sphere */
            while(length>=1.0f){
                cpa->fuv[0]=2.0f*BLI_frand()-1.0f;
                cpa->fuv[1]=2.0f*BLI_frand()-1.0f;
                cpa->fuv[2]=2.0f*BLI_frand()-1.0f;
                length=len_v3(cpa->fuv);
            }

            cpa->num=-1;
        }
    }
    /* dmcache must be updated for parent particles if children from faces is used */
    psys_calc_dmcache(ob, finaldm, psys);
}
static void distribute_grid(DerivedMesh *dm, ParticleSystem *psys)
{
    ParticleData *pa=NULL;
    float min[3], max[3], delta[3], d;
    MVert *mv, *mvert = dm->getVertDataArray(dm,0);
    int totvert=dm->getNumVerts(dm), from=psys->part->from;
    int i, j, k, p, res=psys->part->grid_res, size[3], axis;

    mv=mvert;

    /* find bounding box of dm */
    copy_v3_v3(min, mv->co);
    copy_v3_v3(max, mv->co);
    mv++;

    for(i=1; i<totvert; i++, mv++){
        min[0]=MIN2(min[0],mv->co[0]);
        min[1]=MIN2(min[1],mv->co[1]);
        min[2]=MIN2(min[2],mv->co[2]);

        max[0]=MAX2(max[0],mv->co[0]);
        max[1]=MAX2(max[1],mv->co[1]);
        max[2]=MAX2(max[2],mv->co[2]);
    }

    sub_v3_v3v3(delta, max, min);

    /* determine major axis */
    axis = (delta[0]>=delta[1]) ? 0 : ((delta[1]>=delta[2]) ? 1 : 2);
     
    d = delta[axis]/(float)res;

    size[axis] = res;
    size[(axis+1)%3] = (int)ceil(delta[(axis+1)%3]/d);
    size[(axis+2)%3] = (int)ceil(delta[(axis+2)%3]/d);

    /* float errors grrr.. */
    size[(axis+1)%3] = MIN2(size[(axis+1)%3],res);
    size[(axis+2)%3] = MIN2(size[(axis+2)%3],res);

    size[0] = MAX2(size[0], 1);
    size[1] = MAX2(size[1], 1);
    size[2] = MAX2(size[2], 1);

    /* no full offset for flat/thin objects */
    min[0]+= d < delta[0] ? d/2.f : delta[0]/2.f;
    min[1]+= d < delta[1] ? d/2.f : delta[1]/2.f;
    min[2]+= d < delta[2] ? d/2.f : delta[2]/2.f;

    for(i=0,p=0,pa=psys->particles; i<res; i++){
        for(j=0; j<res; j++){
            for(k=0; k<res; k++,p++,pa++){
                pa->fuv[0] = min[0] + (float)i*d;
                pa->fuv[1] = min[1] + (float)j*d;
                pa->fuv[2] = min[2] + (float)k*d;
                pa->flag |= PARS_UNEXIST;
                pa->hair_index = 0; /* abused in volume calculation */
            }
        }
    }

    /* enable particles near verts/edges/faces/inside surface */
    if(from==PART_FROM_VERT){
        float vec[3];

        pa=psys->particles;

        min[0] -= d/2.0f;
        min[1] -= d/2.0f;
        min[2] -= d/2.0f;

        for(i=0,mv=mvert; i<totvert; i++,mv++){
            sub_v3_v3v3(vec,mv->co,min);
            vec[0]/=delta[0];
            vec[1]/=delta[1];
            vec[2]/=delta[2];
            (pa +((int)(vec[0]*(size[0]-1))*res
                +(int)(vec[1]*(size[1]-1)))*res
                +(int)(vec[2]*(size[2]-1)))->flag &= ~PARS_UNEXIST;
        }
    }
    else if(ELEM(from,PART_FROM_FACE,PART_FROM_VOLUME)){
        float co1[3], co2[3];

        MFace *mface= NULL, *mface_array;
        float v1[3], v2[3], v3[3], v4[4], lambda;
        int a, a1, a2, a0mul, a1mul, a2mul, totface;
        int amax= from==PART_FROM_FACE ? 3 : 1;

        totface=dm->getNumFaces(dm);
        mface_array= dm->getFaceDataArray(dm,CD_MFACE);
        
        for(a=0; a<amax; a++){
            if(a==0){ a0mul=res*res; a1mul=res; a2mul=1; }
            else if(a==1){ a0mul=res; a1mul=1; a2mul=res*res; }
            else{ a0mul=1; a1mul=res*res; a2mul=res; }

            for(a1=0; a1<size[(a+1)%3]; a1++){
                for(a2=0; a2<size[(a+2)%3]; a2++){
                    mface= mface_array;

                    pa = psys->particles + a1*a1mul + a2*a2mul;
                    copy_v3_v3(co1, pa->fuv);
                    co1[a] -= d < delta[a] ? d/2.f : delta[a]/2.f;
                    copy_v3_v3(co2, co1);
                    co2[a] += delta[a] + 0.001f*d;
                    co1[a] -= 0.001f*d;
                    
                    /* lets intersect the faces */
                    for(i=0; i<totface; i++,mface++){
                        copy_v3_v3(v1, mvert[mface->v1].co);
                        copy_v3_v3(v2, mvert[mface->v2].co);
                        copy_v3_v3(v3, mvert[mface->v3].co);

                        if(isect_axial_line_tri_v3(a, co1, co2, v2, v3, v1, &lambda)){
                            if(from==PART_FROM_FACE)
                                (pa+(int)(lambda*size[a])*a0mul)->flag &= ~PARS_UNEXIST;
                            else /* store number of intersections */
                                (pa+(int)(lambda*size[a])*a0mul)->hair_index++;
                        }
                        
                        if(mface->v4){
                            copy_v3_v3(v4, mvert[mface->v4].co);

                            if(isect_axial_line_tri_v3(a, co1, co2, v4, v1, v3, &lambda)){
                                if(from==PART_FROM_FACE)
                                    (pa+(int)(lambda*size[a])*a0mul)->flag &= ~PARS_UNEXIST;
                                else
                                    (pa+(int)(lambda*size[a])*a0mul)->hair_index++;
                            }
                        }
                    }

                    if(from==PART_FROM_VOLUME){
                        int in=pa->hair_index%2;
                        if(in) pa->hair_index++;
                        for(i=0; i<size[0]; i++){
                            if(in || (pa+i*a0mul)->hair_index%2)
                                (pa+i*a0mul)->flag &= ~PARS_UNEXIST;
                            /* odd intersections == in->out / out->in */
                            /* even intersections -> in stays same */
                            in=(in + (pa+i*a0mul)->hair_index) % 2;
                        }
                    }
                }
            }
        }
    }

    if(psys->part->flag & PART_GRID_HEXAGONAL) {
        for(i=0,p=0,pa=psys->particles; i<res; i++){
            for(j=0; j<res; j++){
                for(k=0; k<res; k++,p++,pa++){
                    if(j%2)
                        pa->fuv[0] += d/2.f;

                    if(k%2) {
                        pa->fuv[0] += d/2.f;
                        pa->fuv[1] += d/2.f;
                    }
                }
            }
        }
    }

    if(psys->part->flag & PART_GRID_INVERT){
        for(i=0; i<size[0]; i++){
            for(j=0; j<size[1]; j++){
                pa=psys->particles + res*(i*res + j);
                for(k=0; k<size[2]; k++, pa++){
                    pa->flag ^= PARS_UNEXIST;
                }
            }
        }
    }

    if(psys->part->grid_rand > 0.f) {
        float rfac = d * psys->part->grid_rand;
        for(p=0,pa=psys->particles; p<psys->totpart; p++,pa++){
            if(pa->flag & PARS_UNEXIST)
                continue;

            pa->fuv[0] += rfac * (PSYS_FRAND(p + 31) - 0.5f);
            pa->fuv[1] += rfac * (PSYS_FRAND(p + 32) - 0.5f);
            pa->fuv[2] += rfac * (PSYS_FRAND(p + 33) - 0.5f);
        }
    }
}

/* modified copy from rayshade.c */
static void hammersley_create(float *out, int n, int seed, float amount)
{
    RNG *rng;
    double p, t, offs[2];
    int k, kk;

    rng = rng_new(31415926 + n + seed);
    offs[0]= rng_getDouble(rng) + (double)amount;
    offs[1]= rng_getDouble(rng) + (double)amount;
    rng_free(rng);

    for (k = 0; k < n; k++) {
        t = 0;
        for (p = 0.5, kk = k; kk; p *= 0.5, kk >>= 1)
            if (kk & 1) /* kk mod 2 = 1 */
                t += p;

        out[2*k + 0]= fmod((double)k/(double)n + offs[0], 1.0);
        out[2*k + 1]= fmod(t + offs[1], 1.0);
    }
}

/* modified copy from effect.c */
static void init_mv_jit(float *jit, int num, int seed2, float amount)
{
    RNG *rng;
    float *jit2, x, rad1, rad2, rad3;
    int i, num2;

    if(num==0) return;

    rad1= (float)(1.0f/sqrtf((float)num));
    rad2= (float)(1.0f/((float)num));
    rad3= (float)sqrt((float)num)/((float)num);

    rng = rng_new(31415926 + num + seed2);
    x= 0;
        num2 = 2 * num;
    for(i=0; i<num2; i+=2) {
    
        jit[i]= x + amount*rad1*(0.5f - rng_getFloat(rng));
        jit[i+1]= i/(2.0f*num) + amount*rad1*(0.5f - rng_getFloat(rng));
        
        jit[i]-= (float)floor(jit[i]);
        jit[i+1]-= (float)floor(jit[i+1]);
        
        x+= rad3;
        x -= (float)floor(x);
    }

    jit2= MEM_mallocN(12 + 2*sizeof(float)*num, "initjit");

    for (i=0 ; i<4 ; i++) {
        BLI_jitterate1(jit, jit2, num, rad1);
        BLI_jitterate1(jit, jit2, num, rad1);
        BLI_jitterate2(jit, jit2, num, rad2);
    }
    MEM_freeN(jit2);
    rng_free(rng);
}

static void psys_uv_to_w(float u, float v, int quad, float *w)
{
    float vert[4][3], co[3];

    if(!quad) {
        if(u+v > 1.0f)
            v= 1.0f-v;
        else
            u= 1.0f-u;
    }

    vert[0][0]= 0.0f; vert[0][1]= 0.0f; vert[0][2]= 0.0f;
    vert[1][0]= 1.0f; vert[1][1]= 0.0f; vert[1][2]= 0.0f;
    vert[2][0]= 1.0f; vert[2][1]= 1.0f; vert[2][2]= 0.0f;

    co[0]= u;
    co[1]= v;
    co[2]= 0.0f;

    if(quad) {
        vert[3][0]= 0.0f; vert[3][1]= 1.0f; vert[3][2]= 0.0f;
        interp_weights_poly_v3( w,vert, 4, co);
    }
    else {
        interp_weights_poly_v3( w,vert, 3, co);
        w[3]= 0.0f;
    }
}

/* Find the index in "sum" array before "value" is crossed. */
static int distribute_binary_search(float *sum, int n, float value)
{
    int mid, low=0, high=n;

    if(value == 0.f)
        return 0;

    while(low <= high) {
        mid= (low + high)/2;
        
        if(sum[mid] < value && value <= sum[mid+1])
            return mid;
        
        if(sum[mid] >= value)
            high= mid - 1;
        else if(sum[mid] < value)
            low= mid + 1;
        else
            return mid;
    }

    return low;
}

/* the max number if calls to rng_* funcs within psys_thread_distribute_particle
 * be sure to keep up to date if this changes */
#define PSYS_RND_DIST_SKIP 2

/* note: this function must be thread safe, for from == PART_FROM_CHILD */
#define ONLY_WORKING_WITH_PA_VERTS 0
static void distribute_threads_exec(ParticleThread *thread, ParticleData *pa, ChildParticle *cpa, int p)
{
    ParticleThreadContext *ctx= thread->ctx;
    Object *ob= ctx->sim.ob;
    DerivedMesh *dm= ctx->dm;
    float *v1, *v2, *v3, *v4, nor[3], orco1[3], co1[3], co2[3], nor1[3];
    float cur_d, min_d, randu, randv;
    int from= ctx->from;
    int cfrom= ctx->cfrom;
    int distr= ctx->distr;
    int i, intersect, tot;
    int rng_skip_tot= PSYS_RND_DIST_SKIP; /* count how many rng_* calls wont need skipping */

    if(from == PART_FROM_VERT) {
        /* TODO_PARTICLE - use original index */
        pa->num= ctx->index[p];
        pa->fuv[0] = 1.0f;
        pa->fuv[1] = pa->fuv[2] = pa->fuv[3] = 0.0;

#if ONLY_WORKING_WITH_PA_VERTS
        if(ctx->tree){
            KDTreeNearest ptn[3];
            int w, maxw;

            psys_particle_on_dm(ctx->dm,from,pa->num,pa->num_dmcache,pa->fuv,pa->foffset,co1,0,0,0,orco1,0);
            transform_mesh_orco_verts((Mesh*)ob->data, &orco1, 1, 1);
            maxw = BLI_kdtree_find_n_nearest(ctx->tree,3,orco1,NULL,ptn);

            for(w=0; w<maxw; w++){
                pa->verts[w]=ptn->num;
            }
        }
#endif
    }
    else if(from == PART_FROM_FACE || from == PART_FROM_VOLUME) {
        MFace *mface;

        pa->num = i = ctx->index[p];
        mface = dm->getFaceData(dm,i,CD_MFACE);
        
        switch(distr){
        case PART_DISTR_JIT:
            if(ctx->jitlevel == 1) {
                if(mface->v4)
                    psys_uv_to_w(0.5f, 0.5f, mface->v4, pa->fuv);
                else
                    psys_uv_to_w(0.33333f, 0.33333f, mface->v4, pa->fuv);
            }
            else {
                ctx->jitoff[i] = fmod(ctx->jitoff[i],(float)ctx->jitlevel);
                psys_uv_to_w(ctx->jit[2*(int)ctx->jitoff[i]], ctx->jit[2*(int)ctx->jitoff[i]+1], mface->v4, pa->fuv);
                ctx->jitoff[i]++;
            }
            break;
        case PART_DISTR_RAND:
            randu= rng_getFloat(thread->rng);
            randv= rng_getFloat(thread->rng);
            rng_skip_tot -= 2;

            psys_uv_to_w(randu, randv, mface->v4, pa->fuv);
            break;
        }
        pa->foffset= 0.0f;
        
        /* experimental */
        if(from==PART_FROM_VOLUME){
            MVert *mvert=dm->getVertDataArray(dm,CD_MVERT);

            tot=dm->getNumFaces(dm);

            psys_interpolate_face(mvert,mface,0,0,pa->fuv,co1,nor,0,0,0,0);

            normalize_v3(nor);
            mul_v3_fl(nor,-100.0);

            add_v3_v3v3(co2,co1,nor);

            min_d=2.0;
            intersect=0;

            for(i=0,mface=dm->getFaceDataArray(dm,CD_MFACE); i<tot; i++,mface++){
                if(i==pa->num) continue;

                v1=mvert[mface->v1].co;
                v2=mvert[mface->v2].co;
                v3=mvert[mface->v3].co;

                if(isect_line_tri_v3(co1, co2, v2, v3, v1, &cur_d, 0)){
                    if(cur_d<min_d){
                        min_d=cur_d;
                        pa->foffset=cur_d*50.0f; /* to the middle of volume */
                        intersect=1;
                    }
                }
                if(mface->v4){
                    v4=mvert[mface->v4].co;

                    if(isect_line_tri_v3(co1, co2, v4, v1, v3, &cur_d, 0)){
                        if(cur_d<min_d){
                            min_d=cur_d;
                            pa->foffset=cur_d*50.0f; /* to the middle of volume */
                            intersect=1;
                        }
                    }
                }
            }
            if(intersect==0)
                pa->foffset=0.0;
            else switch(distr){
                case PART_DISTR_JIT:
                    pa->foffset*= ctx->jit[p%(2*ctx->jitlevel)];
                    break;
                case PART_DISTR_RAND:
                    pa->foffset*=BLI_frand();
                    break;
            }
        }
    }
    else if(from == PART_FROM_CHILD) {
        MFace *mf;

        if(ctx->index[p] < 0) {
            cpa->num=0;
            cpa->fuv[0]=cpa->fuv[1]=cpa->fuv[2]=cpa->fuv[3]=0.0f;
            cpa->pa[0]=cpa->pa[1]=cpa->pa[2]=cpa->pa[3]=0;
            return;
        }

        mf= dm->getFaceData(dm, ctx->index[p], CD_MFACE);

        randu= rng_getFloat(thread->rng);
        randv= rng_getFloat(thread->rng);
        rng_skip_tot -= 2;

        psys_uv_to_w(randu, randv, mf->v4, cpa->fuv);

        cpa->num = ctx->index[p];

        if(ctx->tree){
            KDTreeNearest ptn[10];
            int w,maxw;//, do_seams;
            float maxd /*, mind,dd */, totw= 0.0f;
            int parent[10];
            float pweight[10];

            psys_particle_on_dm(dm,cfrom,cpa->num,DMCACHE_ISCHILD,cpa->fuv,cpa->foffset,co1,nor1,NULL,NULL,orco1,NULL);
            transform_mesh_orco_verts((Mesh*)ob->data, &orco1, 1, 1);
            maxw = BLI_kdtree_find_n_nearest(ctx->tree,4,orco1,NULL,ptn);

            maxd=ptn[maxw-1].dist;
            /* mind=ptn[0].dist; */ /* UNUSED */
            
            /* the weights here could be done better */
            for(w=0; w<maxw; w++){
                parent[w]=ptn[w].index;
                pweight[w]=(float)pow(2.0,(double)(-6.0f*ptn[w].dist/maxd));
            }
            for(;w<10; w++){
                parent[w]=-1;
                pweight[w]=0.0f;
            }

            for(w=0,i=0; w<maxw && i<4; w++){
                if(parent[w]>=0){
                    cpa->pa[i]=parent[w];
                    cpa->w[i]=pweight[w];
                    totw+=pweight[w];
                    i++;
                }
            }
            for(;i<4; i++){
                cpa->pa[i]=-1;
                cpa->w[i]=0.0f;
            }

            if(totw>0.0f) for(w=0; w<4; w++)
                cpa->w[w]/=totw;

            cpa->parent=cpa->pa[0];
        }
    }

    if(rng_skip_tot > 0) /* should never be below zero */
        rng_skip(thread->rng, rng_skip_tot);
}

static void *distribute_threads_exec_cb(void *data)
{
    ParticleThread *thread= (ParticleThread*)data;
    ParticleSystem *psys= thread->ctx->sim.psys;
    ParticleData *pa;
    ChildParticle *cpa;
    int p, totpart;

    if(thread->ctx->from == PART_FROM_CHILD) {
        totpart= psys->totchild;
        cpa= psys->child;

        for(p=0; p<totpart; p++, cpa++) {
            if(thread->ctx->skip) /* simplification skip */
                rng_skip(thread->rng, PSYS_RND_DIST_SKIP * thread->ctx->skip[p]);

            if((p+thread->num) % thread->tot == 0)
                distribute_threads_exec(thread, NULL, cpa, p);
            else /* thread skip */
                rng_skip(thread->rng, PSYS_RND_DIST_SKIP);
        }
    }
    else {
        totpart= psys->totpart;
        pa= psys->particles + thread->num;
        for(p=thread->num; p<totpart; p+=thread->tot, pa+=thread->tot)
            distribute_threads_exec(thread, pa, NULL, p);
    }

    return 0;
}

/* not thread safe, but qsort doesn't take userdata argument */
static int *COMPARE_ORIG_INDEX = NULL;
static int distribute_compare_orig_index(const void *p1, const void *p2)
{
    int index1 = COMPARE_ORIG_INDEX[*(const int*)p1];
    int index2 = COMPARE_ORIG_INDEX[*(const int*)p2];

    if(index1 < index2)
        return -1;
    else if(index1 == index2) {
        /* this pointer comparison appears to make qsort stable for glibc,
         * and apparently on solaris too, makes the renders reproducable */
        if(p1 < p2)
            return -1;
        else if(p1 == p2)
            return 0;
        else
            return 1;
    }
    else
        return 1;
}

static void distribute_invalid(Scene *scene, ParticleSystem *psys, int from)
{
    if(from == PART_FROM_CHILD) {
        ChildParticle *cpa;
        int p, totchild = get_psys_tot_child(scene, psys);

        if(psys->child && totchild) {
            for(p=0,cpa=psys->child; p<totchild; p++,cpa++){
                cpa->fuv[0]=cpa->fuv[1]=cpa->fuv[2]=cpa->fuv[3]= 0.0;
                cpa->foffset= 0.0f;
                cpa->parent=0;
                cpa->pa[0]=cpa->pa[1]=cpa->pa[2]=cpa->pa[3]=0;
                cpa->num= -1;
            }
        }
    }
    else {
        PARTICLE_P;
        LOOP_PARTICLES {
            pa->fuv[0]=pa->fuv[1]=pa->fuv[2]= pa->fuv[3]= 0.0;
            pa->foffset= 0.0f;
            pa->num= -1;
        }
    }
}

/* Creates a distribution of coordinates on a DerivedMesh   */
/* This is to denote functionality that does not yet work with mesh - only derived mesh */
static int distribute_threads_init_data(ParticleThread *threads, Scene *scene, DerivedMesh *finaldm, int from)
{
    ParticleThreadContext *ctx= threads[0].ctx;
    Object *ob= ctx->sim.ob;
    ParticleSystem *psys= ctx->sim.psys;
    ParticleData *pa=0, *tpars= 0;
    ParticleSettings *part;
    ParticleSeam *seams= 0;
    KDTree *tree=0;
    DerivedMesh *dm= NULL;
    float *jit= NULL;
    int i, seed, p=0, totthread= threads[0].tot;
    int cfrom=0;
    int totelem=0, totpart, *particle_element=0, children=0, totseam=0;
    int jitlevel= 1, distr;
    float *element_weight=NULL,*element_sum=NULL,*jitter_offset=NULL, *vweight=NULL;
    float cur, maxweight=0.0, tweight, totweight, inv_totweight, co[3], nor[3], orco[3], ornor[3];
    
    if(ELEM3(NULL, ob, psys, psys->part))
        return 0;

    part=psys->part;
    totpart=psys->totpart;
    if(totpart==0)
        return 0;

    if (!finaldm->deformedOnly && !finaldm->getFaceDataArray(finaldm, CD_ORIGINDEX)) {
        printf("Can't create particles with the current modifier stack, disable destructive modifiers\n");
// XXX      error("Can't paint with the current modifier stack, disable destructive modifiers");
        return 0;
    }

    /* First handle special cases */
    if(from == PART_FROM_CHILD) {
        /* Simple children */
        if(part->childtype != PART_CHILD_FACES) {
            BLI_srandom(31415926 + psys->seed + psys->child_seed);
            distribute_simple_children(scene, ob, finaldm, psys);
            return 0;
        }
    }
    else {
        /* Grid distribution */
        if(part->distr==PART_DISTR_GRID && from != PART_FROM_VERT){
            BLI_srandom(31415926 + psys->seed);
            dm= CDDM_from_mesh((Mesh*)ob->data, ob);
            distribute_grid(dm,psys);
            dm->release(dm);
            return 0;
        }
    }
    
    /* Create trees and original coordinates if needed */
    if(from == PART_FROM_CHILD) {
        distr=PART_DISTR_RAND;
        BLI_srandom(31415926 + psys->seed + psys->child_seed);
        dm= finaldm;
        children=1;

        tree=BLI_kdtree_new(totpart);

        for(p=0,pa=psys->particles; p<totpart; p++,pa++){
            psys_particle_on_dm(dm,part->from,pa->num,pa->num_dmcache,pa->fuv,pa->foffset,co,nor,0,0,orco,ornor);
            transform_mesh_orco_verts((Mesh*)ob->data, &orco, 1, 1);
            BLI_kdtree_insert(tree, p, orco, ornor);
        }

        BLI_kdtree_balance(tree);

        totpart = get_psys_tot_child(scene, psys);
        cfrom = from = PART_FROM_FACE;
    }
    else {
        distr = part->distr;
        BLI_srandom(31415926 + psys->seed);
        
        dm= CDDM_from_mesh((Mesh*)ob->data, ob);

        /* we need orco for consistent distributions */
        DM_add_vert_layer(dm, CD_ORCO, CD_ASSIGN, get_mesh_orco_verts(ob));

        if(from == PART_FROM_VERT) {
            MVert *mv= dm->getVertDataArray(dm, CD_MVERT);
            float (*orcodata)[3]= dm->getVertDataArray(dm, CD_ORCO);
            int totvert = dm->getNumVerts(dm);

            tree=BLI_kdtree_new(totvert);

            for(p=0; p<totvert; p++) {
                if(orcodata) {
                    copy_v3_v3(co,orcodata[p]);
                    transform_mesh_orco_verts((Mesh*)ob->data, &co, 1, 1);
                }
                else
                    copy_v3_v3(co,mv[p].co);
                BLI_kdtree_insert(tree,p,co,NULL);
            }

            BLI_kdtree_balance(tree);
        }
    }

    /* Get total number of emission elements and allocate needed arrays */
    totelem = (from == PART_FROM_VERT) ? dm->getNumVerts(dm) : dm->getNumFaces(dm);

    if(totelem == 0){
        distribute_invalid(scene, psys, children ? PART_FROM_CHILD : 0);

        if(G.f & G_DEBUG)
            fprintf(stderr,"Particle distribution error: Nothing to emit from!\n");

        if(dm != finaldm) dm->release(dm);
        return 0;
    }

    element_weight  = MEM_callocN(sizeof(float)*totelem, "particle_distribution_weights");
    particle_element= MEM_callocN(sizeof(int)*totpart, "particle_distribution_indexes");
    element_sum     = MEM_callocN(sizeof(float)*(totelem+1), "particle_distribution_sum");
    jitter_offset   = MEM_callocN(sizeof(float)*totelem, "particle_distribution_jitoff");

    /* Calculate weights from face areas */
    if((part->flag&PART_EDISTR || children) && from != PART_FROM_VERT){
        MVert *v1, *v2, *v3, *v4;
        float totarea=0.f, co1[3], co2[3], co3[3], co4[3];
        float (*orcodata)[3];
        
        orcodata= dm->getVertDataArray(dm, CD_ORCO);

        for(i=0; i<totelem; i++){
            MFace *mf=dm->getFaceData(dm,i,CD_MFACE);

            if(orcodata) {
                copy_v3_v3(co1, orcodata[mf->v1]);
                copy_v3_v3(co2, orcodata[mf->v2]);
                copy_v3_v3(co3, orcodata[mf->v3]);
                transform_mesh_orco_verts((Mesh*)ob->data, &co1, 1, 1);
                transform_mesh_orco_verts((Mesh*)ob->data, &co2, 1, 1);
                transform_mesh_orco_verts((Mesh*)ob->data, &co3, 1, 1);
                if(mf->v4) {
                    copy_v3_v3(co4, orcodata[mf->v4]);
                    transform_mesh_orco_verts((Mesh*)ob->data, &co4, 1, 1);
                }
            }
            else {
                v1= (MVert*)dm->getVertData(dm,mf->v1,CD_MVERT);
                v2= (MVert*)dm->getVertData(dm,mf->v2,CD_MVERT);
                v3= (MVert*)dm->getVertData(dm,mf->v3,CD_MVERT);
                copy_v3_v3(co1, v1->co);
                copy_v3_v3(co2, v2->co);
                copy_v3_v3(co3, v3->co);
                if(mf->v4) {
                    v4= (MVert*)dm->getVertData(dm,mf->v4,CD_MVERT);
                    copy_v3_v3(co4, v4->co);
                }
            }

            cur = mf->v4 ? area_quad_v3(co1, co2, co3, co4) : area_tri_v3(co1, co2, co3);
            
            if(cur > maxweight)
                maxweight = cur;

            element_weight[i] = cur;
            totarea += cur;
        }

        for(i=0; i<totelem; i++)
            element_weight[i] /= totarea;

        maxweight /= totarea;
    }
    else{
        float min=1.0f/(float)(MIN2(totelem,totpart));
        for(i=0; i<totelem; i++)
            element_weight[i]=min;
        maxweight=min;
    }

    /* Calculate weights from vgroup */
    vweight = psys_cache_vgroup(dm,psys,PSYS_VG_DENSITY);

    if(vweight){
        if(from==PART_FROM_VERT) {
            for(i=0;i<totelem; i++)
                element_weight[i]*=vweight[i];
        }
        else { /* PART_FROM_FACE / PART_FROM_VOLUME */
            for(i=0;i<totelem; i++){
                MFace *mf=dm->getFaceData(dm,i,CD_MFACE);
                tweight = vweight[mf->v1] + vweight[mf->v2] + vweight[mf->v3];
                
                if(mf->v4) {
                    tweight += vweight[mf->v4];
                    tweight /= 4.0f;
                }
                else {
                    tweight /= 3.0f;
                }

                element_weight[i]*=tweight;
            }
        }
        MEM_freeN(vweight);
    }

    /* Calculate total weight of all elements */
    totweight= 0.0f;
    for(i=0;i<totelem; i++)
        totweight += element_weight[i];

    inv_totweight = (totweight > 0.f ? 1.f/totweight : 0.f);

    /* Calculate cumulative weights */
    element_sum[0]= 0.0f;
    for(i=0; i<totelem; i++)
        element_sum[i+1]= element_sum[i] + element_weight[i] * inv_totweight;
    
    /* Finally assign elements to particles */
    if((part->flag&PART_TRAND) || (part->simplify_flag&PART_SIMPLIFY_ENABLE)) {
        float pos;

        for(p=0; p<totpart; p++) {
            /* In theory element_sum[totelem] should be 1.0, but due to float errors this is not necessarily always true, so scale pos accordingly. */
            pos= BLI_frand() * element_sum[totelem];
            particle_element[p]= distribute_binary_search(element_sum, totelem, pos);
            particle_element[p]= MIN2(totelem-1, particle_element[p]);
            jitter_offset[particle_element[p]]= pos;
        }
    }
    else {
        double step, pos;
        
        step= (totpart < 2) ? 0.5 : 1.0/(double)totpart;
        pos= 1e-6; /* tiny offset to avoid zero weight face */
        i= 0;

        for(p=0; p<totpart; p++, pos+=step) {
            while((i < totelem) && (pos > element_sum[i+1]))
                i++;

            particle_element[p]= MIN2(totelem-1, i);

            /* avoid zero weight face */
            if(p == totpart-1 && element_weight[particle_element[p]] == 0.0f)
                particle_element[p]= particle_element[p-1];

            jitter_offset[particle_element[p]]= pos;
        }
    }

    MEM_freeN(element_sum);

    /* For hair, sort by origindex (allows optimizations in rendering), */
    /* however with virtual parents the children need to be in random order. */
    if(part->type == PART_HAIR && !(part->childtype==PART_CHILD_FACES && part->parents!=0.0f)) {
        COMPARE_ORIG_INDEX = NULL;

        if(from == PART_FROM_VERT) {
            if(dm->numVertData)
                COMPARE_ORIG_INDEX= dm->getVertDataArray(dm, CD_ORIGINDEX);
        }
        else {
            if(dm->numFaceData)
                COMPARE_ORIG_INDEX= dm->getFaceDataArray(dm, CD_ORIGINDEX);
        }

        if(COMPARE_ORIG_INDEX) {
            qsort(particle_element, totpart, sizeof(int), distribute_compare_orig_index);
            COMPARE_ORIG_INDEX = NULL;
        }
    }

    /* Create jittering if needed */
    if(distr==PART_DISTR_JIT && ELEM(from,PART_FROM_FACE,PART_FROM_VOLUME)) {
        jitlevel= part->userjit;
        
        if(jitlevel == 0) {
            jitlevel= totpart/totelem;
            if(part->flag & PART_EDISTR) jitlevel*= 2;  /* looks better in general, not very scietific */
            if(jitlevel<3) jitlevel= 3;
        }
        
        jit= MEM_callocN((2+ jitlevel*2)*sizeof(float), "jit");

        /* for small amounts of particles we use regular jitter since it looks
         * a bit better, for larger amounts we switch to hammersley sequence 
         * because it is much faster */
        if(jitlevel < 25)
            init_mv_jit(jit, jitlevel, psys->seed, part->jitfac);
        else
            hammersley_create(jit, jitlevel+1, psys->seed, part->jitfac);
        BLI_array_randomize(jit, 2*sizeof(float), jitlevel, psys->seed); /* for custom jit or even distribution */
    }

    /* Setup things for threaded distribution */
    ctx->tree= tree;
    ctx->seams= seams;
    ctx->totseam= totseam;
    ctx->sim.psys= psys;
    ctx->index= particle_element;
    ctx->jit= jit;
    ctx->jitlevel= jitlevel;
    ctx->jitoff= jitter_offset;
    ctx->weight= element_weight;
    ctx->maxweight= maxweight;
    ctx->from= (children)? PART_FROM_CHILD: from;
    ctx->cfrom= cfrom;
    ctx->distr= distr;
    ctx->dm= dm;
    ctx->tpars= tpars;

    if(children) {
        totpart= psys_render_simplify_distribution(ctx, totpart);
        alloc_child_particles(psys, totpart);
    }

    if(!children || psys->totchild < 10000)
        totthread= 1;
    
    seed= 31415926 + ctx->sim.psys->seed;
    for(i=0; i<totthread; i++) {
        threads[i].rng= rng_new(seed);
        threads[i].tot= totthread;
    }

    return 1;
}

static void distribute_particles_on_dm(ParticleSimulationData *sim, int from)
{
    DerivedMesh *finaldm = sim->psmd->dm;
    ListBase threads;
    ParticleThread *pthreads;
    ParticleThreadContext *ctx;
    int i, totthread;

    pthreads= psys_threads_create(sim);

    if(!distribute_threads_init_data(pthreads, sim->scene, finaldm, from)) {
        psys_threads_free(pthreads);
        return;
    }

    totthread= pthreads[0].tot;
    if(totthread > 1) {
        BLI_init_threads(&threads, distribute_threads_exec_cb, totthread);

        for(i=0; i<totthread; i++)
            BLI_insert_thread(&threads, &pthreads[i]);

        BLI_end_threads(&threads);
    }
    else
        distribute_threads_exec_cb(&pthreads[0]);

    psys_calc_dmcache(sim->ob, finaldm, sim->psys);

    ctx= pthreads[0].ctx;
    if(ctx->dm != finaldm)
        ctx->dm->release(ctx->dm);

    psys_threads_free(pthreads);
}

/* ready for future use, to emit particles without geometry */
static void distribute_particles_on_shape(ParticleSimulationData *sim, int UNUSED(from))
{
    distribute_invalid(sim->scene, sim->psys, 0);

    fprintf(stderr,"Shape emission not yet possible!\n");
}

static void distribute_particles(ParticleSimulationData *sim, int from)
{
    PARTICLE_PSMD;
    int distr_error=0;

    if(psmd){
        if(psmd->dm)
            distribute_particles_on_dm(sim, from);
        else
            distr_error=1;
    }
    else
        distribute_particles_on_shape(sim, from);

    if(distr_error){
        distribute_invalid(sim->scene, sim->psys, from);

        fprintf(stderr,"Particle distribution error!\n");
    }
}

/* threaded child particle distribution and path caching */
ParticleThread *psys_threads_create(ParticleSimulationData *sim)
{
    ParticleThread *threads;
    ParticleThreadContext *ctx;
    int i, totthread;

    if(sim->scene->r.mode & R_FIXED_THREADS)
        totthread= sim->scene->r.threads;
    else
        totthread= BLI_system_thread_count();
    
    threads= MEM_callocN(sizeof(ParticleThread)*totthread, "ParticleThread");
    ctx= MEM_callocN(sizeof(ParticleThreadContext), "ParticleThreadContext");

    ctx->sim = *sim;
    ctx->dm= ctx->sim.psmd->dm;
    ctx->ma= give_current_material(sim->ob, sim->psys->part->omat);

    memset(threads, 0, sizeof(ParticleThread)*totthread);

    for(i=0; i<totthread; i++) {
        threads[i].ctx= ctx;
        threads[i].num= i;
        threads[i].tot= totthread;
    }

    return threads;
}

void psys_threads_free(ParticleThread *threads)
{
    ParticleThreadContext *ctx= threads[0].ctx;
    int i, totthread= threads[0].tot;

    /* path caching */
    if(ctx->vg_length)
        MEM_freeN(ctx->vg_length);
    if(ctx->vg_clump)
        MEM_freeN(ctx->vg_clump);
    if(ctx->vg_kink)
        MEM_freeN(ctx->vg_kink);
    if(ctx->vg_rough1)
        MEM_freeN(ctx->vg_rough1);
    if(ctx->vg_rough2)
        MEM_freeN(ctx->vg_rough2);
    if(ctx->vg_roughe)
        MEM_freeN(ctx->vg_roughe);

    if(ctx->sim.psys->lattice){
        end_latt_deform(ctx->sim.psys->lattice);
        ctx->sim.psys->lattice= NULL;
    }

    /* distribution */
    if(ctx->jit) MEM_freeN(ctx->jit);
    if(ctx->jitoff) MEM_freeN(ctx->jitoff);
    if(ctx->weight) MEM_freeN(ctx->weight);
    if(ctx->index) MEM_freeN(ctx->index);
    if(ctx->skip) MEM_freeN(ctx->skip);
    if(ctx->seams) MEM_freeN(ctx->seams);
    //if(ctx->vertpart) MEM_freeN(ctx->vertpart);
    BLI_kdtree_free(ctx->tree);

    /* threads */
    for(i=0; i<totthread; i++) {
        if(threads[i].rng)
            rng_free(threads[i].rng);
        if(threads[i].rng_path)
            rng_free(threads[i].rng_path);
    }

    MEM_freeN(ctx);
    MEM_freeN(threads);
}

/* set particle parameters that don't change during particle's life */
void initialize_particle(ParticleSimulationData *sim, ParticleData *pa, int p)
{
    ParticleSystem *psys = sim->psys;
    ParticleSettings *part = psys->part;
    ParticleTexture ptex;

    pa->flag &= ~PARS_UNEXIST;

    if(part->type != PART_FLUID) {
        psys_get_texture(sim, pa, &ptex, PAMAP_INIT, 0.f);
        
        if(ptex.exist < PSYS_FRAND(p+125))
            pa->flag |= PARS_UNEXIST;

        pa->time = (part->type == PART_HAIR) ? 0.f : part->sta + (part->end - part->sta)*ptex.time;
    }

    pa->hair_index = 0;
    /* we can't reset to -1 anymore since we've figured out correct index in distribute_particles */
    /* usage other than straight after distribute has to handle this index by itself - jahka*/
    //pa->num_dmcache = DMCACHE_NOTFOUND; /* assume we dont have a derived mesh face */
}
static void initialize_all_particles(ParticleSimulationData *sim)
{
    ParticleSystem *psys = sim->psys;
    PARTICLE_P;

    psys->totunexist = 0;

    LOOP_PARTICLES {
        if((pa->flag & PARS_UNEXIST)==0)
            initialize_particle(sim, pa, p);

        if(pa->flag & PARS_UNEXIST)
            psys->totunexist++;
    }

    /* Free unexisting particles. */
    if(psys->totpart && psys->totunexist == psys->totpart) {
        if(psys->particles->boid)
            MEM_freeN(psys->particles->boid);

        MEM_freeN(psys->particles);
        psys->particles = NULL;
        psys->totpart = psys->totunexist = 0;
    }

    if(psys->totunexist) {
        int newtotpart = psys->totpart - psys->totunexist;
        ParticleData *npa, *newpars;
        
        npa = newpars = MEM_callocN(newtotpart * sizeof(ParticleData), "particles");

        for(p=0, pa=psys->particles; p<newtotpart; p++, pa++, npa++) {
            while(pa->flag & PARS_UNEXIST)
                pa++;

            memcpy(npa, pa, sizeof(ParticleData));
        }

        if(psys->particles->boid)
            MEM_freeN(psys->particles->boid);
        MEM_freeN(psys->particles);
        psys->particles = newpars;
        psys->totpart -= psys->totunexist;

        if(psys->particles->boid) {
            BoidParticle *newboids = MEM_callocN(psys->totpart * sizeof(BoidParticle), "boid particles");

            LOOP_PARTICLES
                pa->boid = newboids++;

        }
    }
}
void psys_get_birth_coordinates(ParticleSimulationData *sim, ParticleData *pa, ParticleKey *state, float dtime, float cfra)
{
    Object *ob = sim->ob;
    ParticleSystem *psys = sim->psys;
    ParticleSettings *part;
    ParticleTexture ptex;
    float fac, phasefac, nor[3]={0,0,0},loc[3],vel[3]={0.0,0.0,0.0},rot[4],q2[4];
    float r_vel[3],r_ave[3],r_rot[4],vec[3],p_vel[3]={0.0,0.0,0.0};
    float x_vec[3]={1.0,0.0,0.0}, utan[3]={0.0,1.0,0.0}, vtan[3]={0.0,0.0,1.0}, rot_vec[3]={0.0,0.0,0.0};
    float q_phase[4];
    int p = pa - psys->particles;
    part=psys->part;

    /* get birth location from object       */
    if(part->tanfac != 0.f)
        psys_particle_on_emitter(sim->psmd, part->from,pa->num, pa->num_dmcache, pa->fuv,pa->foffset,loc,nor,utan,vtan,0,0);
    else
        psys_particle_on_emitter(sim->psmd, part->from,pa->num, pa->num_dmcache, pa->fuv,pa->foffset,loc,nor,0,0,0,0);
        
    /* get possible textural influence */
    psys_get_texture(sim, pa, &ptex, PAMAP_IVEL, cfra);

    /* particles live in global space so    */
    /* let's convert:                       */
    /* -location                            */
    mul_m4_v3(ob->obmat, loc);
        
    /* -normal                              */
    mul_mat3_m4_v3(ob->obmat, nor);
    normalize_v3(nor);

    /* -tangent                             */
    if(part->tanfac!=0.0f){
        //float phase=vg_rot?2.0f*(psys_particle_value_from_verts(sim->psmd->dm,part->from,pa,vg_rot)-0.5f):0.0f;
        float phase=0.0f;
        mul_v3_fl(vtan,-cosf((float)M_PI*(part->tanphase+phase)));
        fac= -sinf((float)M_PI*(part->tanphase+phase));
        madd_v3_v3fl(vtan, utan, fac);

        mul_mat3_m4_v3(ob->obmat,vtan);

        copy_v3_v3(utan, nor);
        mul_v3_fl(utan,dot_v3v3(vtan,nor));
        sub_v3_v3(vtan, utan);
            
        normalize_v3(vtan);
    }
        

    /* -velocity (boids need this even if there's no random velocity) */
    if(part->randfac != 0.0f || (part->phystype==PART_PHYS_BOIDS && pa->boid)){
        r_vel[0] = 2.0f * (PSYS_FRAND(p + 10) - 0.5f);
        r_vel[1] = 2.0f * (PSYS_FRAND(p + 11) - 0.5f);
        r_vel[2] = 2.0f * (PSYS_FRAND(p + 12) - 0.5f);

        mul_mat3_m4_v3(ob->obmat, r_vel);
        normalize_v3(r_vel);
    }

    /* -angular velocity                    */
    if(part->avemode==PART_AVE_RAND){
        r_ave[0] = 2.0f * (PSYS_FRAND(p + 13) - 0.5f);
        r_ave[1] = 2.0f * (PSYS_FRAND(p + 14) - 0.5f);
        r_ave[2] = 2.0f * (PSYS_FRAND(p + 15) - 0.5f);

        mul_mat3_m4_v3(ob->obmat,r_ave);
        normalize_v3(r_ave);
    }
        
    /* -rotation                            */
    if(part->randrotfac != 0.0f){
        r_rot[0] = 2.0f * (PSYS_FRAND(p + 16) - 0.5f);
        r_rot[1] = 2.0f * (PSYS_FRAND(p + 17) - 0.5f);
        r_rot[2] = 2.0f * (PSYS_FRAND(p + 18) - 0.5f);
        r_rot[3] = 2.0f * (PSYS_FRAND(p + 19) - 0.5f);
        normalize_qt(r_rot);

        mat4_to_quat(rot,ob->obmat);
        mul_qt_qtqt(r_rot,r_rot,rot);
    }

    if(part->phystype==PART_PHYS_BOIDS && pa->boid) {
        float dvec[3], q[4], mat[3][3];

        copy_v3_v3(state->co,loc);

        /* boids don't get any initial velocity  */
        zero_v3(state->vel);

        /* boids store direction in ave */
        if(fabsf(nor[2])==1.0f) {
            sub_v3_v3v3(state->ave, loc, ob->obmat[3]);
            normalize_v3(state->ave);
        }
        else {
            copy_v3_v3(state->ave, nor);
        }

        /* calculate rotation matrix */
        project_v3_v3v3(dvec, r_vel, state->ave);
        sub_v3_v3v3(mat[0], state->ave, dvec);
        normalize_v3(mat[0]);
        negate_v3_v3(mat[2], r_vel);
        normalize_v3(mat[2]);
        cross_v3_v3v3(mat[1], mat[2], mat[0]);
        
        /* apply rotation */
        mat3_to_quat_is_ok( q,mat);
        copy_qt_qt(state->rot, q);
    }
    else {
        /* conversion done so now we apply new: */
        /* -velocity from:                      */

        /*      *reactions                      */
        if(dtime > 0.f){
            sub_v3_v3v3(vel, pa->state.vel, pa->prev_state.vel);
        }

        /*      *emitter velocity               */
        if(dtime != 0.f && part->obfac != 0.f){
            sub_v3_v3v3(vel, loc, state->co);
            mul_v3_fl(vel, part->obfac/dtime);
        }
        
        /*      *emitter normal                 */
        if(part->normfac != 0.f)
            madd_v3_v3fl(vel, nor, part->normfac);
        
        /*      *emitter tangent                */
        if(sim->psmd && part->tanfac != 0.f)
            madd_v3_v3fl(vel, vtan, part->tanfac);

        /*      *emitter object orientation     */
        if(part->ob_vel[0] != 0.f) {
            normalize_v3_v3(vec, ob->obmat[0]);
            madd_v3_v3fl(vel, vec, part->ob_vel[0]);
        }
        if(part->ob_vel[1] != 0.f) {
            normalize_v3_v3(vec, ob->obmat[1]);
            madd_v3_v3fl(vel, vec, part->ob_vel[1]);
        }
        if(part->ob_vel[2] != 0.f) {
            normalize_v3_v3(vec, ob->obmat[2]);
            madd_v3_v3fl(vel, vec, part->ob_vel[2]);
        }

        /*      *texture                        */
        /* TODO */

        /*      *random                         */
        if(part->randfac != 0.f)
            madd_v3_v3fl(vel, r_vel, part->randfac);

        /*      *particle                       */
        if(part->partfac != 0.f)
            madd_v3_v3fl(vel, p_vel, part->partfac);
        
        mul_v3_v3fl(state->vel, vel, ptex.ivel);

        /* -location from emitter               */
        copy_v3_v3(state->co,loc);

        /* -rotation                            */
        unit_qt(state->rot);

        if(part->rotmode){
            /* create vector into which rotation is aligned */
            switch(part->rotmode){
                case PART_ROT_NOR:
                    copy_v3_v3(rot_vec, nor);
                    break;
                case PART_ROT_VEL:
                    copy_v3_v3(rot_vec, vel);
                    break;
                case PART_ROT_GLOB_X:
                case PART_ROT_GLOB_Y:
                case PART_ROT_GLOB_Z:
                    rot_vec[part->rotmode - PART_ROT_GLOB_X] = 1.0f;
                    break;
                case PART_ROT_OB_X:
                case PART_ROT_OB_Y:
                case PART_ROT_OB_Z:
                    copy_v3_v3(rot_vec, ob->obmat[part->rotmode - PART_ROT_OB_X]);
                    break;
            }
            
            /* create rotation quat */
            negate_v3(rot_vec);
            vec_to_quat( q2,rot_vec, OB_POSX, OB_POSZ);

            /* randomize rotation quat */
            if(part->randrotfac!=0.0f)
                interp_qt_qtqt(rot, q2, r_rot, part->randrotfac);
            else
                copy_qt_qt(rot,q2);

            /* rotation phase */
            phasefac = part->phasefac;
            if(part->randphasefac != 0.0f)
                phasefac += part->randphasefac * PSYS_FRAND(p + 20);
            axis_angle_to_quat( q_phase,x_vec, phasefac*(float)M_PI);

            /* combine base rotation & phase */
            mul_qt_qtqt(state->rot, rot, q_phase);
        }

        /* -angular velocity                    */

        zero_v3(state->ave);

        if(part->avemode){
            switch(part->avemode){
                case PART_AVE_SPIN:
                    copy_v3_v3(state->ave, vel);
                    break;
                case PART_AVE_RAND:
                    copy_v3_v3(state->ave, r_ave);
                    break;
            }
            normalize_v3(state->ave);
            mul_v3_fl(state->ave, part->avefac);
        }
    }
}
/* sets particle to the emitter surface with initial velocity & rotation */
void reset_particle(ParticleSimulationData *sim, ParticleData *pa, float dtime, float cfra)
{
    Object *ob = sim->ob;
    ParticleSystem *psys = sim->psys;
    ParticleSettings *part;
    ParticleTexture ptex;
    int p = pa - psys->particles;
    part=psys->part;
    
    /* get precise emitter matrix if particle is born */
    if(part->type!=PART_HAIR && dtime > 0.f && pa->time < cfra && pa->time >= sim->psys->cfra) {
        /* we have to force RECALC_ANIM here since where_is_objec_time only does drivers */
        while(ob) {
            BKE_animsys_evaluate_animdata(sim->scene, &ob->id, ob->adt, pa->time, ADT_RECALC_ANIM);
            ob = ob->parent;
        }
        ob = sim->ob;
        where_is_object_time(sim->scene, ob, pa->time);
    }

    psys_get_birth_coordinates(sim, pa, &pa->state, dtime, cfra);

    if(part->phystype==PART_PHYS_BOIDS && pa->boid) {
        BoidParticle *bpa = pa->boid;

        /* and gravity in r_ve */
        bpa->gravity[0] = bpa->gravity[1] = 0.0f;
        bpa->gravity[2] = -1.0f;
        if((sim->scene->physics_settings.flag & PHYS_GLOBAL_GRAVITY)
            && sim->scene->physics_settings.gravity[2]!=0.0f)
            bpa->gravity[2] = sim->scene->physics_settings.gravity[2];

        bpa->data.health = part->boids->health;
        bpa->data.mode = eBoidMode_InAir;
        bpa->data.state_id = ((BoidState*)part->boids->states.first)->id;
        bpa->data.acc[0]=bpa->data.acc[1]=bpa->data.acc[2]=0.0f;
    }


    if(part->type == PART_HAIR){
        pa->lifetime = 100.0f;
    }
    else{
        /* get possible textural influence */
        psys_get_texture(sim, pa, &ptex, PAMAP_LIFE, cfra);

        pa->lifetime = part->lifetime * ptex.life;

        if(part->randlife != 0.0f)
            pa->lifetime *= 1.0f - part->randlife * PSYS_FRAND(p + 21);
    }

    pa->dietime = pa->time + pa->lifetime;

    if(sim->psys->pointcache && sim->psys->pointcache->flag & PTCACHE_BAKED &&
        sim->psys->pointcache->mem_cache.first) {
        float dietime = psys_get_dietime_from_cache(sim->psys->pointcache, p);
        pa->dietime = MIN2(pa->dietime, dietime);
    }

    if(pa->time > cfra)
        pa->alive = PARS_UNBORN;
    else if(pa->dietime <= cfra)
        pa->alive = PARS_DEAD;
    else
        pa->alive = PARS_ALIVE;

    pa->state.time = cfra;
}
static void reset_all_particles(ParticleSimulationData *sim, float dtime, float cfra, int from)
{
    ParticleData *pa;
    int p, totpart=sim->psys->totpart;
    
    for(p=from, pa=sim->psys->particles+from; p<totpart; p++, pa++)
        reset_particle(sim, pa, dtime, cfra);
}
/************************************************/
/*          Particle targets                    */
/************************************************/
ParticleSystem *psys_get_target_system(Object *ob, ParticleTarget *pt)
{
    ParticleSystem *psys = NULL;

    if(pt->ob == NULL || pt->ob == ob)
        psys = BLI_findlink(&ob->particlesystem, pt->psys-1);
    else
        psys = BLI_findlink(&pt->ob->particlesystem, pt->psys-1);

    if(psys)
        pt->flag |= PTARGET_VALID;
    else
        pt->flag &= ~PTARGET_VALID;

    return psys;
}
/************************************************/
/*          Keyed particles                     */
/************************************************/
/* Counts valid keyed targets */
void psys_count_keyed_targets(ParticleSimulationData *sim)
{
    ParticleSystem *psys = sim->psys, *kpsys;
    ParticleTarget *pt = psys->targets.first;
    int keys_valid = 1;
    psys->totkeyed = 0;

    for(; pt; pt=pt->next) {
        kpsys = psys_get_target_system(sim->ob, pt);

        if(kpsys && kpsys->totpart) {
            psys->totkeyed += keys_valid;
            if(psys->flag & PSYS_KEYED_TIMING && pt->duration != 0.0f)
                psys->totkeyed += 1;
        }
        else {
            keys_valid = 0;
        }
    }

    psys->totkeyed *= psys->flag & PSYS_KEYED_TIMING ? 1 : psys->part->keyed_loops;
}

static void set_keyed_keys(ParticleSimulationData *sim)
{
    ParticleSystem *psys = sim->psys;
    ParticleSimulationData ksim= {0};
    ParticleTarget *pt;
    PARTICLE_P;
    ParticleKey *key;
    int totpart = psys->totpart, k, totkeys = psys->totkeyed;
    int keyed_flag = 0;

    ksim.scene= sim->scene;
    
    /* no proper targets so let's clear and bail out */
    if(psys->totkeyed==0) {
        free_keyed_keys(psys);
        psys->flag &= ~PSYS_KEYED;
        return;
    }

    if(totpart && psys->particles->totkey != totkeys) {
        free_keyed_keys(psys);
        
        key = MEM_callocN(totpart*totkeys*sizeof(ParticleKey), "Keyed keys");
        
        LOOP_PARTICLES {
            pa->keys = key;
            pa->totkey = totkeys;
            key += totkeys;
        }
    }
    
    psys->flag &= ~PSYS_KEYED;


    pt = psys->targets.first;
    for(k=0; k<totkeys; k++) {
        ksim.ob = pt->ob ? pt->ob : sim->ob;
        ksim.psys = BLI_findlink(&ksim.ob->particlesystem, pt->psys - 1);
        keyed_flag = (ksim.psys->flag & PSYS_KEYED);
        ksim.psys->flag &= ~PSYS_KEYED;

        LOOP_PARTICLES {
            key = pa->keys + k;
            key->time = -1.0; /* use current time */

            psys_get_particle_state(&ksim, p%ksim.psys->totpart, key, 1);

            if(psys->flag & PSYS_KEYED_TIMING){
                key->time = pa->time + pt->time;
                if(pt->duration != 0.0f && k+1 < totkeys) {
                    copy_particle_key(key+1, key, 1);
                    (key+1)->time = pa->time + pt->time + pt->duration;
                }
            }
            else if(totkeys > 1)
                key->time = pa->time + (float)k / (float)(totkeys - 1) * pa->lifetime;
            else
                key->time = pa->time;
        }

        if(psys->flag & PSYS_KEYED_TIMING && pt->duration!=0.0f)
            k++;

        ksim.psys->flag |= keyed_flag;

        pt = (pt->next && pt->next->flag & PTARGET_VALID)? pt->next : psys->targets.first;
    }

    psys->flag |= PSYS_KEYED;
}

/************************************************/
/*          Point Cache                         */
/************************************************/
void psys_make_temp_pointcache(Object *ob, ParticleSystem *psys)
{
    PointCache *cache = psys->pointcache;

    if(cache->flag & PTCACHE_DISK_CACHE && cache->mem_cache.first == NULL) {
        PTCacheID pid;
        BKE_ptcache_id_from_particles(&pid, ob, psys);
        cache->flag &= ~PTCACHE_DISK_CACHE;
        BKE_ptcache_disk_to_mem(&pid);
        cache->flag |= PTCACHE_DISK_CACHE;
    }
}
static void psys_clear_temp_pointcache(ParticleSystem *psys)
{
    if(psys->pointcache->flag & PTCACHE_DISK_CACHE)
        BKE_ptcache_free_mem(&psys->pointcache->mem_cache);
}
void psys_get_pointcache_start_end(Scene *scene, ParticleSystem *psys, int *sfra, int *efra)
{
    ParticleSettings *part = psys->part;

    *sfra = MAX2(1, (int)part->sta);
    *efra = MIN2((int)(part->end + part->lifetime + 1.0f), scene->r.efra);
}

/************************************************/
/*          Effectors                           */
/************************************************/
static void psys_update_particle_bvhtree(ParticleSystem *psys, float cfra)
{
    if(psys) {
        PARTICLE_P;
        int totpart = 0;

        if(!psys->bvhtree || psys->bvhtree_frame != cfra) {
            LOOP_SHOWN_PARTICLES {
                totpart++;
            }
            
            BLI_bvhtree_free(psys->bvhtree);
            psys->bvhtree = BLI_bvhtree_new(totpart, 0.0, 4, 6);

            LOOP_SHOWN_PARTICLES {
                if(pa->alive == PARS_ALIVE) {
                    if(pa->state.time == cfra)
                        BLI_bvhtree_insert(psys->bvhtree, p, pa->prev_state.co, 1);
                    else
                        BLI_bvhtree_insert(psys->bvhtree, p, pa->state.co, 1);
                }
            }
            BLI_bvhtree_balance(psys->bvhtree);

            psys->bvhtree_frame = cfra;
        }
    }
}
void psys_update_particle_tree(ParticleSystem *psys, float cfra)
{
    if(psys) {
        PARTICLE_P;
        int totpart = 0;

        if(!psys->tree || psys->tree_frame != cfra) {
            LOOP_SHOWN_PARTICLES {
                totpart++;
            }

            BLI_kdtree_free(psys->tree);
            psys->tree = BLI_kdtree_new(psys->totpart);

            LOOP_SHOWN_PARTICLES {
                if(pa->alive == PARS_ALIVE) {
                    if(pa->state.time == cfra)
                        BLI_kdtree_insert(psys->tree, p, pa->prev_state.co, NULL);
                    else
                        BLI_kdtree_insert(psys->tree, p, pa->state.co, NULL);
                }
            }
            BLI_kdtree_balance(psys->tree);

            psys->tree_frame = cfra;
        }
    }
}

static void psys_update_effectors(ParticleSimulationData *sim)
{
    pdEndEffectors(&sim->psys->effectors);
    sim->psys->effectors = pdInitEffectors(sim->scene, sim->ob, sim->psys, sim->psys->part->effector_weights);
    precalc_guides(sim, sim->psys->effectors);
}

static void integrate_particle(ParticleSettings *part, ParticleData *pa, float dtime, float *external_acceleration, void (*force_func)(void *forcedata, ParticleKey *state, float *force, float *impulse), void *forcedata)
{
    ParticleKey states[5];
    float force[3],acceleration[3],impulse[3],dx[4][3],dv[4][3],oldpos[3];
    float pa_mass= (part->flag & PART_SIZEMASS ? part->mass * pa->size : part->mass);
    int i, steps=1;
    int integrator = part->integrator;

    copy_v3_v3(oldpos, pa->state.co);
    
    /* Verlet integration behaves strangely with moving emitters, so do first step with euler. */
    if(pa->prev_state.time < 0.f && integrator == PART_INT_VERLET)
        integrator = PART_INT_EULER;

    switch(integrator){
        case PART_INT_EULER:
            steps=1;
            break;
        case PART_INT_MIDPOINT:
            steps=2;
            break;
        case PART_INT_RK4:
            steps=4;
            break;
        case PART_INT_VERLET:
            steps=1;
            break;
    }

    copy_particle_key(states, &pa->state, 1);

    states->time = 0.f;

    for(i=0; i<steps; i++){
        zero_v3(force);
        zero_v3(impulse);

        force_func(forcedata, states+i, force, impulse);

        /* force to acceleration*/
        mul_v3_v3fl(acceleration, force, 1.0f/pa_mass);

        if(external_acceleration)
            add_v3_v3(acceleration, external_acceleration);
        
        /* calculate next state */
        add_v3_v3(states[i].vel, impulse);

        switch(integrator){
            case PART_INT_EULER:
                madd_v3_v3v3fl(pa->state.co, states->co, states->vel, dtime);
                madd_v3_v3v3fl(pa->state.vel, states->vel, acceleration, dtime);
                break;
            case PART_INT_MIDPOINT:
                if(i==0){
                    madd_v3_v3v3fl(states[1].co, states->co, states->vel, dtime*0.5f);
                    madd_v3_v3v3fl(states[1].vel, states->vel, acceleration, dtime*0.5f);
                    states[1].time = dtime*0.5f;
                    /*fra=sim->psys->cfra+0.5f*dfra;*/
                }
                else{
                    madd_v3_v3v3fl(pa->state.co, states->co, states[1].vel, dtime);
                    madd_v3_v3v3fl(pa->state.vel, states->vel, acceleration, dtime);
                }
                break;
            case PART_INT_RK4:
                switch(i){
                    case 0:
                        copy_v3_v3(dx[0], states->vel);
                        mul_v3_fl(dx[0], dtime);
                        copy_v3_v3(dv[0], acceleration);
                        mul_v3_fl(dv[0], dtime);

                        madd_v3_v3v3fl(states[1].co, states->co, dx[0], 0.5f);
                        madd_v3_v3v3fl(states[1].vel, states->vel, dv[0], 0.5f);
                        states[1].time = dtime*0.5f;
                        /*fra=sim->psys->cfra+0.5f*dfra;*/
                        break;
                    case 1:
                        madd_v3_v3v3fl(dx[1], states->vel, dv[0], 0.5f);
                        mul_v3_fl(dx[1], dtime);
                        copy_v3_v3(dv[1], acceleration);
                        mul_v3_fl(dv[1], dtime);

                        madd_v3_v3v3fl(states[2].co, states->co, dx[1], 0.5f);
                        madd_v3_v3v3fl(states[2].vel, states->vel, dv[1], 0.5f);
                        states[2].time = dtime*0.5f;
                        break;
                    case 2:
                        madd_v3_v3v3fl(dx[2], states->vel, dv[1], 0.5f);
                        mul_v3_fl(dx[2], dtime);
                        copy_v3_v3(dv[2], acceleration);
                        mul_v3_fl(dv[2], dtime);

                        add_v3_v3v3(states[3].co, states->co, dx[2]);
                        add_v3_v3v3(states[3].vel, states->vel, dv[2]);
                        states[3].time = dtime;
                        /*fra=cfra;*/
                        break;
                    case 3:
                        add_v3_v3v3(dx[3], states->vel, dv[2]);
                        mul_v3_fl(dx[3], dtime);
                        copy_v3_v3(dv[3], acceleration);
                        mul_v3_fl(dv[3], dtime);

                        madd_v3_v3v3fl(pa->state.co, states->co, dx[0], 1.0f/6.0f);
                        madd_v3_v3fl(pa->state.co, dx[1], 1.0f/3.0f);
                        madd_v3_v3fl(pa->state.co, dx[2], 1.0f/3.0f);
                        madd_v3_v3fl(pa->state.co, dx[3], 1.0f/6.0f);

                        madd_v3_v3v3fl(pa->state.vel, states->vel, dv[0], 1.0f/6.0f);
                        madd_v3_v3fl(pa->state.vel, dv[1], 1.0f/3.0f);
                        madd_v3_v3fl(pa->state.vel, dv[2], 1.0f/3.0f);
                        madd_v3_v3fl(pa->state.vel, dv[3], 1.0f/6.0f);
                }
                break;
            case PART_INT_VERLET:   /* Verlet integration */
                madd_v3_v3v3fl(pa->state.vel, pa->prev_state.vel, acceleration, dtime);
                madd_v3_v3v3fl(pa->state.co, pa->prev_state.co, pa->state.vel, dtime);

                sub_v3_v3v3(pa->state.vel, pa->state.co, oldpos);
                mul_v3_fl(pa->state.vel, 1.0f/dtime);
                break;
        }
    }
}

/*********************************************************************************************************
                    SPH fluid physics 

 In theory, there could be unlimited implementation of SPH simulators

 This code uses in some parts adapted algorithms from the pseudo code as outlined in the Research paper:

 Titled: Particle-based Viscoelastic Fluid Simulation.
 Authors: Simon Clavet, Philippe Beaudoin and Pierre Poulin
 Website: http://www.iro.umontreal.ca/labs/infographie/papers/Clavet-2005-PVFS/

 Presented at Siggraph, (2005)

***********************************************************************************************************/
#define PSYS_FLUID_SPRINGS_INITIAL_SIZE 256
static ParticleSpring *sph_spring_add(ParticleSystem *psys, ParticleSpring *spring)
{
    /* Are more refs required? */
    if(psys->alloc_fluidsprings == 0 || psys->fluid_springs == NULL) {
        psys->alloc_fluidsprings = PSYS_FLUID_SPRINGS_INITIAL_SIZE;
        psys->fluid_springs = (ParticleSpring*)MEM_callocN(psys->alloc_fluidsprings * sizeof(ParticleSpring), "Particle Fluid Springs");
    }
    else if(psys->tot_fluidsprings == psys->alloc_fluidsprings) {
        /* Double the number of refs allocated */
        psys->alloc_fluidsprings *= 2;
        psys->fluid_springs = (ParticleSpring*)MEM_reallocN(psys->fluid_springs, psys->alloc_fluidsprings * sizeof(ParticleSpring));
    }

    memcpy(psys->fluid_springs + psys->tot_fluidsprings, spring, sizeof(ParticleSpring));
    psys->tot_fluidsprings++;

    return psys->fluid_springs + psys->tot_fluidsprings - 1;
}
static void sph_spring_delete(ParticleSystem *psys, int j)
{
    if (j != psys->tot_fluidsprings - 1)
        psys->fluid_springs[j] = psys->fluid_springs[psys->tot_fluidsprings - 1];

    psys->tot_fluidsprings--;

    if (psys->tot_fluidsprings < psys->alloc_fluidsprings/2 && psys->alloc_fluidsprings > PSYS_FLUID_SPRINGS_INITIAL_SIZE){
        psys->alloc_fluidsprings /= 2;
        psys->fluid_springs = (ParticleSpring*)MEM_reallocN(psys->fluid_springs,  psys->alloc_fluidsprings * sizeof(ParticleSpring));
    }
}
static void sph_springs_modify(ParticleSystem *psys, float dtime)
{
    SPHFluidSettings *fluid = psys->part->fluid;
    ParticleData *pa1, *pa2;
    ParticleSpring *spring = psys->fluid_springs;
    
    float h, d, Rij[3], rij, Lij;
    int i;

    float yield_ratio = fluid->yield_ratio;
    float plasticity = fluid->plasticity_constant;
    /* scale things according to dtime */
    float timefix = 25.f * dtime;

    if((fluid->flag & SPH_VISCOELASTIC_SPRINGS)==0 || fluid->spring_k == 0.f)
        return;

    /* Loop through the springs */
    for(i=0; i<psys->tot_fluidsprings; i++, spring++) {
        pa1 = psys->particles + spring->particle_index[0];
        pa2 = psys->particles + spring->particle_index[1];

        sub_v3_v3v3(Rij, pa2->prev_state.co, pa1->prev_state.co);
        rij = normalize_v3(Rij);

        /* adjust rest length */
        Lij = spring->rest_length;
        d = yield_ratio * timefix * Lij;

        if (rij > Lij + d) // Stretch
            spring->rest_length += plasticity * (rij - Lij - d) * timefix;
        else if(rij < Lij - d) // Compress
            spring->rest_length -= plasticity * (Lij - d - rij) * timefix;

        h = 4.f*pa1->size;

        if(spring->rest_length > h)
            spring->delete_flag = 1;
    }

    /* Loop through springs backwaqrds - for efficient delete function */
    for (i=psys->tot_fluidsprings-1; i >= 0; i--) {
        if(psys->fluid_springs[i].delete_flag)
            sph_spring_delete(psys, i);
    }
}
static EdgeHash *sph_springhash_build(ParticleSystem *psys)
{
    EdgeHash *springhash = NULL;
    ParticleSpring *spring;
    int i = 0;

    springhash = BLI_edgehash_new();

    for(i=0, spring=psys->fluid_springs; i<psys->tot_fluidsprings; i++, spring++)
        BLI_edgehash_insert(springhash, spring->particle_index[0], spring->particle_index[1], SET_INT_IN_POINTER(i+1));

    return springhash;
}

#define SPH_NEIGHBORS 512
typedef struct SPHNeighbor
{
    ParticleSystem *psys;
    int index;
} SPHNeighbor;
typedef struct SPHRangeData
{
    SPHNeighbor neighbors[SPH_NEIGHBORS];
    int tot_neighbors;

    float density, near_density;
    float h;

    ParticleSystem *npsys;
    ParticleData *pa;

    float massfac;
    int use_size;
} SPHRangeData;
typedef struct SPHData {
    ParticleSystem *psys[10];
    ParticleData *pa;
    float mass;
    EdgeHash *eh;
    float *gravity;
    /* Average distance to neighbours (other particles in the support domain),
       for calculating the Courant number (adaptive time step). */
    int pass;
    float element_size;
    float flow[3];

    /* Integrator callbacks. This allows different SPH implementations. */
    void (*force_cb) (void *sphdata_v, ParticleKey *state, float *force, float *impulse);
    void (*density_cb) (void *rangedata_v, int index, float squared_dist);
}SPHData;

static void sph_density_accum_cb(void *userdata, int index, float squared_dist)
{
    SPHRangeData *pfr = (SPHRangeData *)userdata;
    ParticleData *npa = pfr->npsys->particles + index;
    float q;
    float dist;

    if(npa == pfr->pa || squared_dist < FLT_EPSILON)
        return;

    /* Ugh! One particle has too many neighbors! If some aren't taken into
     * account, the forces will be biased by the tree search order. This
     * effectively adds enery to the system, and results in a churning motion.
     * But, we have to stop somewhere, and it's not the end of the world.
     *  - jahka and z0r
     */
    if(pfr->tot_neighbors >= SPH_NEIGHBORS)
        return;

    pfr->neighbors[pfr->tot_neighbors].index = index;
    pfr->neighbors[pfr->tot_neighbors].psys = pfr->npsys;
    pfr->tot_neighbors++;

    dist = sqrtf(squared_dist);
    q = (1.f - dist/pfr->h) * pfr->massfac;

    if(pfr->use_size)
        q *= npa->size;

    pfr->density += q*q;
    pfr->near_density += q*q*q;
}
/*
 * Find the Courant number for an SPH particle (used for adaptive time step).
 */
static void sph_particle_courant(SPHData *sphdata, SPHRangeData *pfr) {
    ParticleData *pa, *npa;
    int i;
    float flow[3], offset[3], dist;

    flow[0] = flow[1] = flow[2] = 0.0f;
    dist = 0.0f;
    if (pfr->tot_neighbors > 0) {
        pa = pfr->pa;
        for (i=0; i < pfr->tot_neighbors; i++) {
            npa = pfr->neighbors[i].psys->particles + pfr->neighbors[i].index;
            sub_v3_v3v3(offset, pa->prev_state.co, npa->prev_state.co);
            dist += len_v3(offset);
            add_v3_v3(flow, npa->prev_state.vel);
        }
        dist += sphdata->psys[0]->part->fluid->radius; // TODO: remove this? - z0r
        sphdata->element_size = dist / pfr->tot_neighbors;
        mul_v3_v3fl(sphdata->flow, flow, 1.0f / pfr->tot_neighbors);
    } else {
        sphdata->element_size = MAXFLOAT;
        VECCOPY(sphdata->flow, flow);
    }
}
static void sph_force_cb(void *sphdata_v, ParticleKey *state, float *force, float *UNUSED(impulse))
{
    SPHData *sphdata = (SPHData *)sphdata_v;
    ParticleSystem **psys = sphdata->psys;
    ParticleData *pa = sphdata->pa;
    SPHFluidSettings *fluid = psys[0]->part->fluid;
    ParticleSpring *spring = NULL;
    SPHRangeData pfr;
    SPHNeighbor *pfn;
    float mass = sphdata->mass;
    float *gravity = sphdata->gravity;
    EdgeHash *springhash = sphdata->eh;

    float q, u, rij, dv[3];
    float pressure, near_pressure;

    float visc = fluid->viscosity_omega;
    float stiff_visc = fluid->viscosity_beta * (fluid->flag & SPH_FAC_VISCOSITY ? fluid->viscosity_omega : 1.f);

    float inv_mass = 1.0f/mass;
    float spring_constant = fluid->spring_k;
    
    float h = fluid->radius * (fluid->flag & SPH_FAC_RADIUS ? 4.f*pa->size : 1.f); /* 4.0 seems to be a pretty good value */
    float rest_density = fluid->rest_density * (fluid->flag & SPH_FAC_DENSITY ? 4.77f : 1.f); /* 4.77 is an experimentally determined density factor */
    float rest_length = fluid->rest_length * (fluid->flag & SPH_FAC_REST_LENGTH ? 2.588f * pa->size : 1.f);

    float stiffness = fluid->stiffness_k;
    float stiffness_near_fac = fluid->stiffness_knear * (fluid->flag & SPH_FAC_REPULSION ? fluid->stiffness_k : 1.f);

    ParticleData *npa;
    float vec[3];
    float vel[3];
    float co[3];

    int i, spring_index, index = pa - psys[0]->particles;

    pfr.tot_neighbors = 0;
    pfr.density = pfr.near_density = 0.f;
    pfr.h = h;
    pfr.pa = pa;

    for(i=0; i<10 && psys[i]; i++) {
        pfr.npsys = psys[i];
        pfr.massfac = psys[i]->part->mass*inv_mass;
        pfr.use_size = psys[i]->part->flag & PART_SIZEMASS;

        BLI_bvhtree_range_query(psys[i]->bvhtree, state->co, h, sphdata->density_cb, &pfr);
    }

    pressure =  stiffness * (pfr.density - rest_density);
    near_pressure = stiffness_near_fac * pfr.near_density;

    pfn = pfr.neighbors;
    for(i=0; i<pfr.tot_neighbors; i++, pfn++) {
        npa = pfn->psys->particles + pfn->index;

        madd_v3_v3v3fl(co, npa->prev_state.co, npa->prev_state.vel, state->time);

        sub_v3_v3v3(vec, co, state->co);
        rij = normalize_v3(vec);

        q = (1.f - rij/h) * pfn->psys->part->mass * inv_mass;

        if(pfn->psys->part->flag & PART_SIZEMASS)
            q *= npa->size;

        copy_v3_v3(vel, npa->prev_state.vel);

        /* Double Density Relaxation */
        madd_v3_v3fl(force, vec, -(pressure + near_pressure*q)*q);

        /* Viscosity */
        if(visc > 0.f   || stiff_visc > 0.f) {      
            sub_v3_v3v3(dv, vel, state->vel);
            u = dot_v3v3(vec, dv);

            if(u < 0.f && visc > 0.f)
                madd_v3_v3fl(force, vec, 0.5f * q * visc * u );

            if(u > 0.f && stiff_visc > 0.f)
                madd_v3_v3fl(force, vec, 0.5f * q * stiff_visc * u );
        }

        if(spring_constant > 0.f) {
            /* Viscoelastic spring force */
            if (pfn->psys == psys[0] && fluid->flag & SPH_VISCOELASTIC_SPRINGS && springhash) {
                /* BLI_edgehash_lookup appears to be thread-safe. - z0r */
                spring_index = GET_INT_FROM_POINTER(BLI_edgehash_lookup(springhash, index, pfn->index));

                if(spring_index) {
                    spring = psys[0]->fluid_springs + spring_index - 1;

                    madd_v3_v3fl(force, vec, -10.f * spring_constant * (1.f - rij/h) * (spring->rest_length - rij));
                }
                else if(fluid->spring_frames == 0 || (pa->prev_state.time-pa->time) <= fluid->spring_frames){
                    ParticleSpring temp_spring;
                    temp_spring.particle_index[0] = index;
                    temp_spring.particle_index[1] = pfn->index;
                    temp_spring.rest_length = (fluid->flag & SPH_CURRENT_REST_LENGTH) ? rij : rest_length;
                    temp_spring.delete_flag = 0;

                    /* sph_spring_add is not thread-safe. - z0r */
                    #pragma omp critical
                    sph_spring_add(psys[0], &temp_spring);
                }
            }
            else {/* PART_SPRING_HOOKES - Hooke's spring force */
                madd_v3_v3fl(force, vec, -10.f * spring_constant * (1.f - rij/h) * (rest_length - rij));
            }
        }
    }
    
    /* Artificial buoyancy force in negative gravity direction  */
    if (fluid->buoyancy > 0.f && gravity)
        madd_v3_v3fl(force, gravity, fluid->buoyancy * (pfr.density-rest_density));

    if (sphdata->pass == 0 && psys[0]->part->time_flag & PART_TIME_AUTOSF)
        sph_particle_courant(sphdata, &pfr);
    sphdata->pass++;
}

static void sph_solver_init(ParticleSimulationData *sim, SPHData *sphdata) {
    ParticleTarget *pt;
    int i;

    // Add other coupled particle systems.
    sphdata->psys[0] = sim->psys;
    for(i=1, pt=sim->psys->targets.first; i<10; i++, pt=(pt?pt->next:NULL))
        sphdata->psys[i] = pt ? psys_get_target_system(sim->ob, pt) : NULL;

    if (psys_uses_gravity(sim))
        sphdata->gravity = sim->scene->physics_settings.gravity;
    else
        sphdata->gravity = NULL;
    sphdata->eh = sph_springhash_build(sim->psys);

    // These per-particle values should be overridden later, but just for
    // completeness we give them default values now.
    sphdata->pa = NULL;
    sphdata->mass = 1.0f;

    sphdata->force_cb = sph_force_cb;
    sphdata->density_cb = sph_density_accum_cb;
}
static void sph_solver_finalise(SPHData *sphdata) {
    if (sphdata->eh) {
        BLI_edgehash_free(sphdata->eh, NULL);
        sphdata->eh = NULL;
    }
}
static void sph_integrate(ParticleSimulationData *sim, ParticleData *pa, float dfra, SPHData *sphdata){
    ParticleSettings *part = sim->psys->part;
    // float timestep = psys_get_timestep(sim); // UNUSED
    float pa_mass = part->mass * (part->flag & PART_SIZEMASS ? pa->size : 1.f);
    float dtime = dfra*psys_get_timestep(sim);
    // int steps = 1; // UNUSED
    float effector_acceleration[3];

    sphdata->pa = pa;
    sphdata->mass = pa_mass;
    sphdata->pass = 0;
    //sphdata.element_size and sphdata.flow are set in the callback.

    /* restore previous state and treat gravity & effectors as external acceleration*/
    sub_v3_v3v3(effector_acceleration, pa->state.vel, pa->prev_state.vel);
    mul_v3_fl(effector_acceleration, 1.f/dtime);

    copy_particle_key(&pa->state, &pa->prev_state, 0);

    integrate_particle(part, pa, dtime, effector_acceleration, sphdata->force_cb, sphdata);
}

/************************************************/
/*          Basic physics                       */
/************************************************/
typedef struct EfData
{
    ParticleTexture ptex;
    ParticleSimulationData *sim;
    ParticleData *pa;
} EfData;
static void basic_force_cb(void *efdata_v, ParticleKey *state, float *force, float *impulse)
{
    EfData *efdata = (EfData *)efdata_v;
    ParticleSimulationData *sim = efdata->sim;
    ParticleSettings *part = sim->psys->part;
    ParticleData *pa = efdata->pa;
    EffectedPoint epoint;

    /* add effectors */
    pd_point_from_particle(efdata->sim, efdata->pa, state, &epoint);
    if(part->type != PART_HAIR || part->effector_weights->flag & EFF_WEIGHT_DO_HAIR)
        pdDoEffectors(sim->psys->effectors, sim->colliders, part->effector_weights, &epoint, force, impulse);

    mul_v3_fl(force, efdata->ptex.field);
    mul_v3_fl(impulse, efdata->ptex.field);

    /* calculate air-particle interaction */
    if(part->dragfac != 0.0f)
        madd_v3_v3fl(force, state->vel, -part->dragfac * pa->size * pa->size * len_v3(state->vel));

    /* brownian force */
    if(part->brownfac != 0.0f){
        force[0] += (BLI_frand()-0.5f) * part->brownfac;
        force[1] += (BLI_frand()-0.5f) * part->brownfac;
        force[2] += (BLI_frand()-0.5f) * part->brownfac;
    }
}
/* gathers all forces that effect particles and calculates a new state for the particle */
static void basic_integrate(ParticleSimulationData *sim, int p, float dfra, float cfra)
{
    ParticleSettings *part = sim->psys->part;
    ParticleData *pa = sim->psys->particles + p;
    ParticleKey tkey;
    float dtime=dfra*psys_get_timestep(sim), time;
    float *gravity = NULL, gr[3];
    EfData efdata;

    psys_get_texture(sim, pa, &efdata.ptex, PAMAP_PHYSICS, cfra);

    efdata.pa = pa;
    efdata.sim = sim;

    /* add global acceleration (gravitation) */
    if(psys_uses_gravity(sim)
        /* normal gravity is too strong for hair so it's disabled by default */
        && (part->type != PART_HAIR || part->effector_weights->flag & EFF_WEIGHT_DO_HAIR)) {
        zero_v3(gr);
        madd_v3_v3fl(gr, sim->scene->physics_settings.gravity, part->effector_weights->global_gravity * efdata.ptex.gravity);
        gravity = gr;
    }

    /* maintain angular velocity */
    copy_v3_v3(pa->state.ave, pa->prev_state.ave);

    integrate_particle(part, pa, dtime, gravity, basic_force_cb, &efdata);

    /* damp affects final velocity */
    if(part->dampfac != 0.f)
        mul_v3_fl(pa->state.vel, 1.f - part->dampfac * efdata.ptex.damp * 25.f * dtime);

    //copy_v3_v3(pa->state.ave, states->ave);

    /* finally we do guides */
    time=(cfra-pa->time)/pa->lifetime;
    CLAMP(time, 0.0f, 1.0f);

    copy_v3_v3(tkey.co,pa->state.co);
    copy_v3_v3(tkey.vel,pa->state.vel);
    tkey.time=pa->state.time;

    if(part->type != PART_HAIR) {
        if(do_guides(sim->psys->effectors, &tkey, p, time)) {
            copy_v3_v3(pa->state.co,tkey.co);
            /* guides don't produce valid velocity */
            sub_v3_v3v3(pa->state.vel, tkey.co, pa->prev_state.co);
            mul_v3_fl(pa->state.vel,1.0f/dtime);
            pa->state.time=tkey.time;
        }
    }
}
static void basic_rotate(ParticleSettings *part, ParticleData *pa, float dfra, float timestep)
{
    float rotfac, rot1[4], rot2[4]={1.0,0.0,0.0,0.0}, dtime=dfra*timestep;

    if((part->flag & PART_ROT_DYN)==0){
        if(part->avemode==PART_AVE_SPIN){
            float angle;
            float len1 = len_v3(pa->prev_state.vel);
            float len2 = len_v3(pa->state.vel);

            if(len1==0.0f || len2==0.0f)
                pa->state.ave[0]=pa->state.ave[1]=pa->state.ave[2]=0.0f;
            else{
                cross_v3_v3v3(pa->state.ave,pa->prev_state.vel,pa->state.vel);
                normalize_v3(pa->state.ave);
                angle=dot_v3v3(pa->prev_state.vel,pa->state.vel)/(len1*len2);
                mul_v3_fl(pa->state.ave,saacos(angle)/dtime);
            }

            axis_angle_to_quat(rot2,pa->state.vel,dtime*part->avefac);
        }
    }

    rotfac=len_v3(pa->state.ave);
    if(rotfac == 0.0f){ /* unit_qt(in VecRotToQuat) doesn't give unit quat [1,0,0,0]?? */
        rot1[0]=1.0f;
        rot1[1]=rot1[2]=rot1[3]=0;
    }
    else{
        axis_angle_to_quat(rot1,pa->state.ave,rotfac*dtime);
    }
    mul_qt_qtqt(pa->state.rot,rot1,pa->prev_state.rot);
    mul_qt_qtqt(pa->state.rot,rot2,pa->state.rot);

    /* keep rotation quat in good health */
    normalize_qt(pa->state.rot);
}

/************************************************/
/*          Collisions                          */
/************************************************/
#define COLLISION_MAX_COLLISIONS    10
#define COLLISION_MIN_RADIUS 0.001f
#define COLLISION_MIN_DISTANCE 0.0001f
#define COLLISION_ZERO 0.00001f
typedef float (*NRDistanceFunc)(float *p, float radius, ParticleCollisionElement *pce, float *nor);
static float nr_signed_distance_to_plane(float *p, float radius, ParticleCollisionElement *pce, float *nor)
{
    float p0[3], e1[3], e2[3], d;

    sub_v3_v3v3(e1, pce->x1, pce->x0);
    sub_v3_v3v3(e2, pce->x2, pce->x0);
    sub_v3_v3v3(p0, p, pce->x0);

    cross_v3_v3v3(nor, e1, e2);
    normalize_v3(nor);

    d = dot_v3v3(p0, nor);

    if(pce->inv_nor == -1) {
        if(d < 0.f)
            pce->inv_nor = 1;
        else
            pce->inv_nor = 0;
    }

    if(pce->inv_nor == 1) {
        negate_v3(nor);
        d = -d;
    }

    return d - radius;
}
static float nr_distance_to_edge(float *p, float radius, ParticleCollisionElement *pce, float *UNUSED(nor))
{
    float v0[3], v1[3], v2[3], c[3];

    sub_v3_v3v3(v0, pce->x1, pce->x0);
    sub_v3_v3v3(v1, p, pce->x0);
    sub_v3_v3v3(v2, p, pce->x1);

    cross_v3_v3v3(c, v1, v2);

    return fabsf(len_v3(c)/len_v3(v0)) - radius;
}
static float nr_distance_to_vert(float *p, float radius, ParticleCollisionElement *pce, float *UNUSED(nor))
{
    return len_v3v3(p, pce->x0) - radius;
}
static void collision_interpolate_element(ParticleCollisionElement *pce, float t, float fac, ParticleCollision *col)
{
    /* t is the current time for newton rhapson */
    /* fac is the starting factor for current collision iteration */
    /* the col->fac's are factors for the particle subframe step start and end during collision modifier step */
    float f = fac + t*(1.f-fac);
    float mul = col->fac1 + f * (col->fac2-col->fac1);
    if(pce->tot > 0) {
        madd_v3_v3v3fl(pce->x0, pce->x[0], pce->v[0], mul);

        if(pce->tot > 1) {
            madd_v3_v3v3fl(pce->x1, pce->x[1], pce->v[1], mul);

            if(pce->tot > 2)
                madd_v3_v3v3fl(pce->x2, pce->x[2], pce->v[2], mul);
        }
    }
}
static void collision_point_velocity(ParticleCollisionElement *pce)
{
    float v[3];

    copy_v3_v3(pce->vel, pce->v[0]);

    if(pce->tot > 1) {
        sub_v3_v3v3(v, pce->v[1], pce->v[0]);
        madd_v3_v3fl(pce->vel, v, pce->uv[0]);

        if(pce->tot > 2) {
            sub_v3_v3v3(v, pce->v[2], pce->v[0]);
            madd_v3_v3fl(pce->vel, v, pce->uv[1]);
        }
    }
}
static float collision_point_distance_with_normal(float p[3], ParticleCollisionElement *pce, float fac, ParticleCollision *col, float *nor)
{
    if(fac >= 0.f)
        collision_interpolate_element(pce, 0.f, fac, col);

    switch(pce->tot) {
        case 1:
        {
            sub_v3_v3v3(nor, p, pce->x0);
            return normalize_v3(nor);
        }
        case 2:
        {
            float u, e[3], vec[3];
            sub_v3_v3v3(e, pce->x1, pce->x0);
            sub_v3_v3v3(vec, p, pce->x0);
            u = dot_v3v3(vec, e) / dot_v3v3(e, e);

            madd_v3_v3v3fl(nor, vec, e, -u);
            return normalize_v3(nor);
        }
        case 3:
            return nr_signed_distance_to_plane(p, 0.f, pce, nor);
    }
    return 0;
}
static void collision_point_on_surface(float p[3], ParticleCollisionElement *pce, float fac, ParticleCollision *col, float *co)
{
    collision_interpolate_element(pce, 0.f, fac, col);

    switch(pce->tot) {
        case 1:
        {
            sub_v3_v3v3(co, p, pce->x0);
            normalize_v3(co);
            madd_v3_v3v3fl(co, pce->x0, co, col->radius);
            break;
        }
        case 2:
        {
            float u, e[3], vec[3], nor[3];
            sub_v3_v3v3(e, pce->x1, pce->x0);
            sub_v3_v3v3(vec, p, pce->x0);
            u = dot_v3v3(vec, e) / dot_v3v3(e, e);

            madd_v3_v3v3fl(nor, vec, e, -u);
            normalize_v3(nor);

            madd_v3_v3v3fl(co, pce->x0, e, pce->uv[0]);
            madd_v3_v3fl(co, nor, col->radius);
            break;
        }
        case 3:
        {
                float p0[3], e1[3], e2[3], nor[3];

                sub_v3_v3v3(e1, pce->x1, pce->x0);
                sub_v3_v3v3(e2, pce->x2, pce->x0);
                sub_v3_v3v3(p0, p, pce->x0);

                cross_v3_v3v3(nor, e1, e2);
                normalize_v3(nor);

                if(pce->inv_nor == 1)
                    negate_v3(nor);

                madd_v3_v3v3fl(co, pce->x0, nor, col->radius);
                madd_v3_v3fl(co, e1, pce->uv[0]);
                madd_v3_v3fl(co, e2, pce->uv[1]);
            break;
        }
    }
}
/* find first root in range [0-1] starting from 0 */
static float collision_newton_rhapson(ParticleCollision *col, float radius, ParticleCollisionElement *pce, NRDistanceFunc distance_func)
{
    float t0, t1, d0, d1, dd, n[3];
    int iter;

    pce->inv_nor = -1;

    /* start from the beginning */
    t0 = 0.f;
    collision_interpolate_element(pce, t0, col->f, col);
    d0 = distance_func(col->co1, radius, pce, n);
    t1 = 0.001f;
    d1 = 0.f;

    for(iter=0; iter<10; iter++) {//, itersum++) {
        /* get current location */
        collision_interpolate_element(pce, t1, col->f, col);
        interp_v3_v3v3(pce->p, col->co1, col->co2, t1);

        d1 = distance_func(pce->p, radius, pce, n);

        /* no movement, so no collision */
        if(d1 == d0) {
            return -1.f;
        }

        /* particle already inside face, so report collision */
        if(iter == 0 && d0 < 0.f && d0 > -radius) {
            copy_v3_v3(pce->p, col->co1);
            copy_v3_v3(pce->nor, n);
            pce->inside = 1;
            return 0.f;
        }
        
        dd = (t1-t0)/(d1-d0);

        t0 = t1;
        d0 = d1;

        t1 -= d1*dd;

        /* particle movin away from plane could also mean a strangely rotating face, so check from end */
        if(iter == 0 && t1 < 0.f) {
            t0 = 1.f;
            collision_interpolate_element(pce, t0, col->f, col);
            d0 = distance_func(col->co2, radius, pce, n);
            t1 = 0.999f;
            d1 = 0.f;

            continue;
        }
        else if(iter == 1 && (t1 < -COLLISION_ZERO || t1 > 1.f))
            return -1.f;

        if(d1 <= COLLISION_ZERO && d1 >= -COLLISION_ZERO) {
            if(t1 >= -COLLISION_ZERO && t1 <= 1.f) {
                if(distance_func == nr_signed_distance_to_plane)
                    copy_v3_v3(pce->nor, n);

                CLAMP(t1, 0.f, 1.f);

                return t1;
            }
            else
                return -1.f;
        }
    }
    return -1.0;
}
static int collision_sphere_to_tri(ParticleCollision *col, float radius, ParticleCollisionElement *pce, float *t)
{
    ParticleCollisionElement *result = &col->pce;
    float ct, u, v;

    pce->inv_nor = -1;
    pce->inside = 0;

    ct = collision_newton_rhapson(col, radius, pce, nr_signed_distance_to_plane);

    if(ct >= 0.f && ct < *t && (result->inside==0 || pce->inside==1) ) {
        float e1[3], e2[3], p0[3];
        float e1e1, e1e2, e1p0, e2e2, e2p0, inv;

        sub_v3_v3v3(e1, pce->x1, pce->x0);
        sub_v3_v3v3(e2, pce->x2, pce->x0);
        /* XXX: add radius correction here? */
        sub_v3_v3v3(p0, pce->p, pce->x0);

        e1e1 = dot_v3v3(e1, e1);
        e1e2 = dot_v3v3(e1, e2);
        e1p0 = dot_v3v3(e1, p0);
        e2e2 = dot_v3v3(e2, e2);
        e2p0 = dot_v3v3(e2, p0);

        inv = 1.f/(e1e1 * e2e2 - e1e2 * e1e2);
        u = (e2e2 * e1p0 - e1e2 * e2p0) * inv;
        v = (e1e1 * e2p0 - e1e2 * e1p0) * inv;

        if(u>=0.f && u<=1.f && v>=0.f && u+v<=1.f) {
            *result = *pce;

            /* normal already calculated in pce */

            result->uv[0] = u;
            result->uv[1] = v;

            *t = ct;
            return 1;
        }
    }
    return 0;
}
static int collision_sphere_to_edges(ParticleCollision *col, float radius, ParticleCollisionElement *pce, float *t)
{
    ParticleCollisionElement edge[3], *cur = NULL, *hit = NULL;
    ParticleCollisionElement *result = &col->pce;

    float ct;
    int i;

    for(i=0; i<3; i++) {
        /* in case of a quad, no need to check "edge" that goes through face twice */
        if((pce->x[3] && i==2))
            continue;

        cur = edge+i;
        cur->x[0] = pce->x[i]; cur->x[1] = pce->x[(i+1)%3];
        cur->v[0] = pce->v[i]; cur->v[1] = pce->v[(i+1)%3];
        cur->tot = 2;
        cur->inside = 0;

        ct = collision_newton_rhapson(col, radius, cur, nr_distance_to_edge);

        if(ct >= 0.f && ct < *t) {
            float u, e[3], vec[3];

            sub_v3_v3v3(e, cur->x1, cur->x0);
            sub_v3_v3v3(vec, cur->p, cur->x0);
            u = dot_v3v3(vec, e) / dot_v3v3(e, e);

            if(u < 0.f || u > 1.f)
                break;

            *result = *cur;

            madd_v3_v3v3fl(result->nor, vec, e, -u);
            normalize_v3(result->nor);

            result->uv[0] = u;

            
            hit = cur;
            *t = ct;
        }

    }

    return hit != NULL;
}
static int collision_sphere_to_verts(ParticleCollision *col, float radius, ParticleCollisionElement *pce, float *t)
{
    ParticleCollisionElement vert[3], *cur = NULL, *hit = NULL;
    ParticleCollisionElement *result = &col->pce;

    float ct;
    int i;

    for(i=0; i<3; i++) {
        /* in case of quad, only check one vert the first time */
        if(pce->x[3] && i != 1)
            continue;

        cur = vert+i;
        cur->x[0] = pce->x[i];
        cur->v[0] = pce->v[i];
        cur->tot = 1;
        cur->inside = 0;

        ct = collision_newton_rhapson(col, radius, cur, nr_distance_to_vert);
        
        if(ct >= 0.f && ct < *t) {
            *result = *cur;

            sub_v3_v3v3(result->nor, cur->p, cur->x0);
            normalize_v3(result->nor);

            hit = cur;
            *t = ct;
        }

    }

    return hit != NULL;
}
/* Callback for BVHTree near test */
void BKE_psys_collision_neartest_cb(void *userdata, int index, const BVHTreeRay *ray, BVHTreeRayHit *hit)
{
    ParticleCollision *col = (ParticleCollision *) userdata;
    ParticleCollisionElement pce;
    MFace *face = col->md->mfaces + index;
    MVert *x = col->md->x;
    MVert *v = col->md->current_v;
    float t = hit->dist/col->original_ray_length;
    int collision = 0;

    pce.x[0] = x[face->v1].co;
    pce.x[1] = x[face->v2].co;
    pce.x[2] = x[face->v3].co;
    pce.x[3] = face->v4 ? x[face->v4].co : NULL;

    pce.v[0] = v[face->v1].co;
    pce.v[1] = v[face->v2].co;
    pce.v[2] = v[face->v3].co;
    pce.v[3] = face->v4 ? v[face->v4].co : NULL;

    pce.tot = 3;
    pce.inside = 0;
    pce.index = index;

    /* don't collide with same face again */
    if(col->hit == col->current && col->pce.index == index && col->pce.tot == 3)
        return;

    do
    {   
        collision = collision_sphere_to_tri(col, ray->radius, &pce, &t);
        if(col->pce.inside == 0) {
            collision += collision_sphere_to_edges(col, ray->radius, &pce, &t);
            collision += collision_sphere_to_verts(col, ray->radius, &pce, &t);
        }

        if(collision) {
            hit->dist = col->original_ray_length * t;
            hit->index = index;
                
            collision_point_velocity(&col->pce);

            col->hit = col->current;
        }

        pce.x[1] = pce.x[2];
        pce.x[2] = pce.x[3];
        pce.x[3] = NULL;

        pce.v[1] = pce.v[2];
        pce.v[2] = pce.v[3];
        pce.v[3] = NULL;

    } while(pce.x[2]);
}
static int collision_detect(ParticleData *pa, ParticleCollision *col, BVHTreeRayHit *hit, ListBase *colliders)
{
    ColliderCache *coll;
    float ray_dir[3];

    if(colliders->first == NULL)
        return 0;

    sub_v3_v3v3(ray_dir, col->co2, col->co1);
    hit->index = -1;
    hit->dist = col->original_ray_length = len_v3(ray_dir);
    col->pce.inside = 0;

    /* even if particle is stationary we want to check for moving colliders */
    /* if hit.dist is zero the bvhtree_ray_cast will just ignore everything */
    if(hit->dist == 0.0f)
        hit->dist = col->original_ray_length = 0.000001f;

    for(coll = colliders->first; coll; coll=coll->next){
        /* for boids: don't check with current ground object */
        if(coll->ob == col->skip)
            continue;

        /* particles should not collide with emitter at birth */
        if(coll->ob == col->emitter && pa->time < col->cfra && pa->time >= col->old_cfra)
            continue;

        col->current = coll->ob;
        col->md = coll->collmd;
        col->fac1 = (col->old_cfra - coll->collmd->time_x) / (coll->collmd->time_xnew - coll->collmd->time_x);
        col->fac2 = (col->cfra - coll->collmd->time_x) / (coll->collmd->time_xnew - coll->collmd->time_x);

        if(col->md && col->md->bvhtree)
            BLI_bvhtree_ray_cast(col->md->bvhtree, col->co1, ray_dir, col->radius, hit, BKE_psys_collision_neartest_cb, col);
    }

    return hit->index >= 0;
}
static int collision_response(ParticleData *pa, ParticleCollision *col, BVHTreeRayHit *hit, int kill, int dynamic_rotation)
{
    ParticleCollisionElement *pce = &col->pce;
    PartDeflect *pd = col->hit->pd;
    float co[3];                                        /* point of collision */
    float x = hit->dist/col->original_ray_length;       /* location factor of collision between this iteration */
    float f = col->f + x * (1.0f - col->f);             /* time factor of collision between timestep */
    float dt1 = (f - col->f) * col->total_time;         /* time since previous collision (in seconds) */
    float dt2 = (1.0f - f) * col->total_time;           /* time left after collision (in seconds) */
    int through = (BLI_frand() < pd->pdef_perm) ? 1 : 0; /* did particle pass through the collision surface? */

    /* calculate exact collision location */
    interp_v3_v3v3(co, col->co1, col->co2, x);

    /* particle dies in collision */
    if(through == 0 && (kill || pd->flag & PDEFLE_KILL_PART)) {
        pa->alive = PARS_DYING;
        pa->dietime = col->old_cfra + (col->cfra - col->old_cfra) * f;

        copy_v3_v3(pa->state.co, co);
        interp_v3_v3v3(pa->state.vel, pa->prev_state.vel, pa->state.vel, f);
        interp_qt_qtqt(pa->state.rot, pa->prev_state.rot, pa->state.rot, f);
        interp_v3_v3v3(pa->state.ave, pa->prev_state.ave, pa->state.ave, f);

        /* particle is dead so we don't need to calculate further */
        return 0;
    }
    /* figure out velocity and other data after collision */
    else {
        float v0[3];    /* velocity directly before collision to be modified into velocity directly after collision */
        float v0_nor[3];/* normal component of v0 */
        float v0_tan[3];/* tangential component of v0 */
        float vc_tan[3];/* tangential component of collision surface velocity */
        float v0_dot, vc_dot;
        float damp = pd->pdef_damp + pd->pdef_rdamp * 2 * (BLI_frand() - 0.5f);
        float frict = pd->pdef_frict + pd->pdef_rfrict * 2 * (BLI_frand() - 0.5f);
        float distance, nor[3], dot;

        CLAMP(damp,0.0f, 1.0f);
        CLAMP(frict,0.0f, 1.0f);

        /* get exact velocity right before collision */
        madd_v3_v3v3fl(v0, col->ve1, col->acc, dt1);
                
        /* convert collider velocity from 1/framestep to 1/s TODO: here we assume 1 frame step for collision modifier */
        mul_v3_fl(pce->vel, col->inv_timestep);

        /* calculate tangential particle velocity */
        v0_dot = dot_v3v3(pce->nor, v0);
        madd_v3_v3v3fl(v0_tan, v0, pce->nor, -v0_dot);

        /* calculate tangential collider velocity */
        vc_dot = dot_v3v3(pce->nor, pce->vel);
        madd_v3_v3v3fl(vc_tan, pce->vel, pce->nor, -vc_dot);

        /* handle friction effects (tangential and angular velocity) */
        if(frict > 0.0f) {
            /* angular <-> linear velocity */
            if(dynamic_rotation) {
                float vr_tan[3], v1_tan[3], ave[3];
                    
                /* linear velocity of particle surface */
                cross_v3_v3v3(vr_tan, pce->nor, pa->state.ave);
                mul_v3_fl(vr_tan, pa->size);

                /* change to coordinates that move with the collision plane */
                sub_v3_v3v3(v1_tan, v0_tan, vc_tan);
                        
                /* The resulting velocity is a weighted average of particle cm & surface
                    * velocity. This weight (related to particle's moment of inertia) could
                    * be made a parameter for angular <-> linear conversion.
                    */
                madd_v3_v3fl(v1_tan, vr_tan, -0.4);
                mul_v3_fl(v1_tan, 1.0f/1.4f); /* 1/(1+0.4) */

                /* rolling friction is around 0.01 of sliding friction (could be made a parameter) */
                mul_v3_fl(v1_tan, 1.0f - 0.01f * frict);

                /* surface_velocity is opposite to cm velocity */
                negate_v3_v3(vr_tan, v1_tan);

                /* get back to global coordinates */
                add_v3_v3(v1_tan, vc_tan);

                /* convert to angular velocity*/
                cross_v3_v3v3(ave, vr_tan, pce->nor);
                mul_v3_fl(ave, 1.0f/MAX2(pa->size, 0.001f));

                /* only friction will cause change in linear & angular velocity */
                interp_v3_v3v3(pa->state.ave, pa->state.ave, ave, frict);
                interp_v3_v3v3(v0_tan, v0_tan, v1_tan, frict);
            }
            else {
                /* just basic friction (unphysical due to the friction model used in Blender) */
                interp_v3_v3v3(v0_tan, v0_tan, vc_tan, frict);
            }
        }

        /* stickness was possibly added before, so cancel that before calculating new normal velocity */
        /* otherwise particles go flying out of the surface because of high reversed sticky velocity */
        if(v0_dot < 0.0f) {
            v0_dot += pd->pdef_stickness;
            if(v0_dot > 0.0f)
                v0_dot = 0.0f;
        }

        /* damping and flipping of velocity around normal */
        v0_dot *= 1.0f - damp;
        vc_dot *= through ? damp : 1.0f;

        /* calculate normal particle velocity */
        /* special case for object hitting the particle from behind */
        if(through==0 && ((vc_dot>0.0f && v0_dot>0.0f && vc_dot>v0_dot) || (vc_dot<0.0f && v0_dot<0.0f && vc_dot<v0_dot)))
            mul_v3_v3fl(v0_nor, pce->nor, vc_dot);
        else if(v0_dot > 0.f)
            mul_v3_v3fl(v0_nor, pce->nor, vc_dot + (through ? -1.0f : 1.0f) * v0_dot);
        else
            mul_v3_v3fl(v0_nor, pce->nor, vc_dot + (through ? 1.0f : -1.0f) * v0_dot);

        /* combine components together again */
        add_v3_v3v3(v0, v0_nor, v0_tan);

        if(col->boid) {
            /* keep boids above ground */
            BoidParticle *bpa = pa->boid;
            if(bpa->data.mode == eBoidMode_OnLand || co[2] <= col->boid_z) {
                co[2] = col->boid_z;
                v0[2] = 0.0f;
            }
        }
        
        /* re-apply acceleration to final location and velocity */
        madd_v3_v3v3fl(pa->state.co, co, v0, dt2);
        madd_v3_v3fl(pa->state.co, col->acc, 0.5f*dt2*dt2);
        madd_v3_v3v3fl(pa->state.vel, v0, col->acc, dt2);

        /* make sure particle stays on the right side of the surface */
        if(!through) {
            distance = collision_point_distance_with_normal(co, pce, -1.f, col, nor);
            
            if(distance < col->radius + COLLISION_MIN_DISTANCE)
                madd_v3_v3fl(co, nor, col->radius + COLLISION_MIN_DISTANCE - distance);

            dot = dot_v3v3(nor, v0);
            if(dot < 0.f)
                madd_v3_v3fl(v0, nor, -dot);

            distance = collision_point_distance_with_normal(pa->state.co, pce, 1.f, col, nor);

            if(distance < col->radius + COLLISION_MIN_DISTANCE)
                madd_v3_v3fl(pa->state.co, nor, col->radius + COLLISION_MIN_DISTANCE - distance);

            dot = dot_v3v3(nor, pa->state.vel);
            if(dot < 0.f)
                madd_v3_v3fl(pa->state.vel, nor, -dot);
        }

        /* add stickness to surface */
        madd_v3_v3fl(pa->state.vel, pce->nor, -pd->pdef_stickness);

        /* set coordinates for next iteration */
        copy_v3_v3(col->co1, co);
        copy_v3_v3(col->co2, pa->state.co);

        copy_v3_v3(col->ve1, v0);
        copy_v3_v3(col->ve2, pa->state.vel);

        col->f = f;
    }

    col->prev = col->hit;
    col->prev_index = hit->index;

    return 1;
}
static void collision_fail(ParticleData *pa, ParticleCollision *col)
{
    /* final chance to prevent total failure, so stick to the surface and hope for the best */
    collision_point_on_surface(col->co1, &col->pce, 1.f, col, pa->state.co);

    copy_v3_v3(pa->state.vel, col->pce.vel);
    mul_v3_fl(pa->state.vel, col->inv_timestep);


    /* printf("max iterations\n"); */
}

/* Particle - Mesh collision detection and response
 * Features:
 * -friction and damping
 * -angular momentum <-> linear momentum
 * -high accuracy by re-applying particle acceleration after collision
 * -handles moving, rotating and deforming meshes
 * -uses Newton-Rhapson iteration to find the collisions
 * -handles spherical particles and (nearly) point like particles
 */
static void collision_check(ParticleSimulationData *sim, int p, float dfra, float cfra)
{
    ParticleSettings *part = sim->psys->part;
    ParticleData *pa = sim->psys->particles + p;
    ParticleCollision col;
    BVHTreeRayHit hit;
    int collision_count=0;

    float timestep = psys_get_timestep(sim);

    memset(&col, 0, sizeof(ParticleCollision));

    col.total_time = timestep * dfra;
    col.inv_timestep = 1.0f/timestep;

    col.cfra = cfra;
    col.old_cfra = sim->psys->cfra;

    /* get acceleration (from gravity, forcefields etc. to be re-applied in collision response) */
    sub_v3_v3v3(col.acc, pa->state.vel, pa->prev_state.vel);
    mul_v3_fl(col.acc, 1.f/col.total_time);

    /* set values for first iteration */
    copy_v3_v3(col.co1, pa->prev_state.co);
    copy_v3_v3(col.co2, pa->state.co);
    copy_v3_v3(col.ve1, pa->prev_state.vel);
    copy_v3_v3(col.ve2, pa->state.vel);
    col.f = 0.0f;

    col.radius = ((part->flag & PART_SIZE_DEFL) || (part->phystype == PART_PHYS_BOIDS)) ? pa->size : COLLISION_MIN_RADIUS;

    /* override for boids */
    if(part->phystype == PART_PHYS_BOIDS && part->boids->options & BOID_ALLOW_LAND) {
        col.boid = 1;
        col.boid_z = pa->state.co[2];
        col.skip = pa->boid->ground;
    }

    /* 10 iterations to catch multiple collisions */
    while(collision_count < COLLISION_MAX_COLLISIONS){
        if(collision_detect(pa, &col, &hit, sim->colliders)) {
            
            collision_count++;

            if(collision_count == COLLISION_MAX_COLLISIONS)
                collision_fail(pa, &col);
            else if(collision_response(pa, &col, &hit, part->flag & PART_DIE_ON_COL, part->flag & PART_ROT_DYN)==0)
                return;
        }
        else
            return;
    }
}
/************************************************/
/*          Hair                                */
/************************************************/
/* check if path cache or children need updating and do it if needed */
static void psys_update_path_cache(ParticleSimulationData *sim, float cfra)
{
    ParticleSystem *psys = sim->psys;
    ParticleSettings *part = psys->part;
    ParticleEditSettings *pset = &sim->scene->toolsettings->particle;
    int distr=0, alloc=0, skip=0;

    if((psys->part->childtype && psys->totchild != get_psys_tot_child(sim->scene, psys)) || psys->recalc&PSYS_RECALC_RESET)
        alloc=1;

    if(alloc || psys->recalc&PSYS_RECALC_CHILD || (psys->vgroup[PSYS_VG_DENSITY] && (sim->ob && sim->ob->mode & OB_MODE_WEIGHT_PAINT)))
        distr=1;

    if(distr){
        if(alloc)
            realloc_particles(sim, sim->psys->totpart);

        if(get_psys_tot_child(sim->scene, psys)) {
            /* don't generate children while computing the hair keys */
            if(!(psys->part->type == PART_HAIR) || (psys->flag & PSYS_HAIR_DONE)) {
                distribute_particles(sim, PART_FROM_CHILD);

                if(part->childtype==PART_CHILD_FACES && part->parents != 0.0f)
                    psys_find_parents(sim);
            }
        }
        else
            psys_free_children(psys);
    }

    if((part->type==PART_HAIR || psys->flag&PSYS_KEYED || psys->pointcache->flag & PTCACHE_BAKED)==0)
        skip = 1; /* only hair, keyed and baked stuff can have paths */
    else if(part->ren_as != PART_DRAW_PATH && !(part->type==PART_HAIR && ELEM(part->ren_as, PART_DRAW_OB, PART_DRAW_GR)))
        skip = 1; /* particle visualization must be set as path */
    else if(!psys->renderdata) {
        if(part->draw_as != PART_DRAW_REND)
            skip = 1; /* draw visualization */
        else if(psys->pointcache->flag & PTCACHE_BAKING)
            skip = 1; /* no need to cache paths while baking dynamics */
        else if(psys_in_edit_mode(sim->scene, psys)) {
            if((pset->flag & PE_DRAW_PART)==0)
                skip = 1;
            else if(part->childtype==0 && (psys->flag & PSYS_HAIR_DYNAMICS && psys->pointcache->flag & PTCACHE_BAKED)==0)
                skip = 1; /* in edit mode paths are needed for child particles and dynamic hair */
        }
    }

    if(!skip) {
        psys_cache_paths(sim, cfra);

        /* for render, child particle paths are computed on the fly */
        if(part->childtype) {
            if(!psys->totchild)
                skip = 1;
            else if(psys->part->type == PART_HAIR && (psys->flag & PSYS_HAIR_DONE)==0)
                skip = 1;

            if(!skip)
                psys_cache_child_paths(sim, cfra, 0);
        }
    }
    else if(psys->pathcache)
        psys_free_path_cache(psys, NULL);
}

static void do_hair_dynamics(ParticleSimulationData *sim)
{
    ParticleSystem *psys = sim->psys;
    DerivedMesh *dm = psys->hair_in_dm;
    MVert *mvert = NULL;
    MEdge *medge = NULL;
    MDeformVert *dvert = NULL;
    HairKey *key;
    PARTICLE_P;
    int totpoint = 0;
    int totedge;
    int k;
    float hairmat[4][4];

    if(!psys->clmd) {
        psys->clmd = (ClothModifierData*)modifier_new(eModifierType_Cloth);
        psys->clmd->sim_parms->goalspring = 0.0f;
        psys->clmd->sim_parms->flags |= CLOTH_SIMSETTINGS_FLAG_GOAL|CLOTH_SIMSETTINGS_FLAG_NO_SPRING_COMPRESS;
        psys->clmd->coll_parms->flags &= ~CLOTH_COLLSETTINGS_FLAG_SELF;
    }

    /* create a dm from hair vertices */
    LOOP_PARTICLES
        totpoint += pa->totkey;

    totedge = totpoint;
    totpoint += psys->totpart;

    if(dm && (totpoint != dm->getNumVerts(dm) || totedge != dm->getNumEdges(dm))) {
        dm->release(dm);
        dm = psys->hair_in_dm = NULL;
    }

    if(!dm) {
        dm = psys->hair_in_dm = CDDM_new(totpoint, totedge, 0);
        DM_add_vert_layer(dm, CD_MDEFORMVERT, CD_CALLOC, NULL);
    }

    mvert = CDDM_get_verts(dm);
    medge = CDDM_get_edges(dm);
    dvert = DM_get_vert_data_layer(dm, CD_MDEFORMVERT);

    psys->clmd->sim_parms->vgroup_mass = 1;

    /* make vgroup for pin roots etc.. */
    psys->particles->hair_index = 1;
    LOOP_PARTICLES {
        if(p)
            pa->hair_index = (pa-1)->hair_index + (pa-1)->totkey + 1;

        psys_mat_hair_to_object(sim->ob, sim->psmd->dm, psys->part->from, pa, hairmat);

        for(k=0, key=pa->hair; k<pa->totkey; k++,key++) {
            
            /* create fake root before actual root to resist bending */
            if(k==0) {
                float temp[3];
                sub_v3_v3v3(temp, key->co, (key+1)->co);
                copy_v3_v3(mvert->co, key->co);
                add_v3_v3v3(mvert->co, mvert->co, temp);
                mul_m4_v3(hairmat, mvert->co);
                mvert++;

                medge->v1 = pa->hair_index - 1;
                medge->v2 = pa->hair_index;
                medge++;

                if(dvert) {
                    if(!dvert->totweight) {
                        dvert->dw = MEM_callocN (sizeof(MDeformWeight), "deformWeight");
                        dvert->totweight = 1;
                    }

                    dvert->dw->weight = 1.0f;
                    dvert++;
                }
            }

            copy_v3_v3(mvert->co, key->co);
            mul_m4_v3(hairmat, mvert->co);
            mvert++;
            
            if(k) {
                medge->v1 = pa->hair_index + k - 1;
                medge->v2 = pa->hair_index + k;
                medge++;
            }

            if(dvert) {
                if(!dvert->totweight) {
                    dvert->dw = MEM_callocN (sizeof(MDeformWeight), "deformWeight");
                    dvert->totweight = 1;
                }
                /* roots should be 1.0, the rest can be anything from 0.0 to 1.0 */
                dvert->dw->weight = key->weight;
                dvert++;
            }
        }
    }

    if(psys->hair_out_dm)
        psys->hair_out_dm->release(psys->hair_out_dm);

    psys->clmd->point_cache = psys->pointcache;
    psys->clmd->sim_parms->effector_weights = psys->part->effector_weights;

    psys->hair_out_dm = clothModifier_do(psys->clmd, sim->scene, sim->ob, dm);

    psys->clmd->sim_parms->effector_weights = NULL;
}
static void hair_step(ParticleSimulationData *sim, float cfra)
{
    ParticleSystem *psys = sim->psys;
    ParticleSettings *part = psys->part;
    PARTICLE_P;
    float disp = (float)psys_get_current_display_percentage(psys)/100.0f;

    LOOP_PARTICLES {
        pa->size = part->size;
        if(part->randsize > 0.0f)
            pa->size *= 1.0f - part->randsize * PSYS_FRAND(p + 1);

        if(PSYS_FRAND(p) > disp)
            pa->flag |= PARS_NO_DISP;
        else
            pa->flag &= ~PARS_NO_DISP;
    }

    if(psys->recalc & PSYS_RECALC_RESET) {
        /* need this for changing subsurf levels */
        psys_calc_dmcache(sim->ob, sim->psmd->dm, psys);

        if(psys->clmd)
            cloth_free_modifier(psys->clmd);
    }

    /* dynamics with cloth simulation, psys->particles can be NULL with 0 particles [#25519] */
    if(psys->part->type==PART_HAIR && psys->flag & PSYS_HAIR_DYNAMICS && psys->particles)
        do_hair_dynamics(sim);

    /* following lines were removed r29079 but cause bug [#22811], see report for details */
    psys_update_effectors(sim);
    psys_update_path_cache(sim, cfra);

    psys->flag |= PSYS_HAIR_UPDATED;
}

static void save_hair(ParticleSimulationData *sim, float UNUSED(cfra))
{
    Object *ob = sim->ob;
    ParticleSystem *psys = sim->psys;
    HairKey *key, *root;
    PARTICLE_P;

    invert_m4_m4(ob->imat, ob->obmat);
    
    psys->lattice= psys_get_lattice(sim);

    if(psys->totpart==0) return;
    
    /* save new keys for elements if needed */
    LOOP_PARTICLES {
        /* first time alloc */
        if(pa->totkey==0 || pa->hair==NULL) {
            pa->hair = MEM_callocN((psys->part->hair_step + 1) * sizeof(HairKey), "HairKeys");
            pa->totkey = 0;
        }

        key = root = pa->hair;
        key += pa->totkey;

        /* convert from global to geometry space */
        copy_v3_v3(key->co, pa->state.co);
        mul_m4_v3(ob->imat, key->co);

        if(pa->totkey) {
            sub_v3_v3(key->co, root->co);
            psys_vec_rot_to_face(sim->psmd->dm, pa, key->co);
        }

        key->time = pa->state.time;

        key->weight = 1.0f - key->time / 100.0f;

        pa->totkey++;

        /* root is always in the origin of hair space so we set it to be so after the last key is saved*/
        if(pa->totkey == psys->part->hair_step + 1)
            root->co[0] = root->co[1] = root->co[2] = 0.0f;
    }
}

/* Code for an adaptive time step based on the Courant-Friedrichs-Lewy
   condition. */
#define MIN_TIMESTEP 1.0f / 101.0f
/* Tolerance of 1.5 means the last subframe neither favours growing nor
   shrinking (e.g if it were 1.3, the last subframe would tend to be too
   small). */
#define TIMESTEP_EXPANSION_TOLERANCE 1.5f

/* Calculate the speed of the particle relative to the local scale of the
   simulation. This should be called once per particle during a simulation
   step, after the velocity has been updated. element_size defines the scale of
   the simulation, and is typically the distance to neighbourning particles. */
void update_courant_num(ParticleSimulationData *sim, ParticleData *pa,
    float dtime, SPHData *sphdata)
{
    float relative_vel[3];
    float speed;

    sub_v3_v3v3(relative_vel, pa->prev_state.vel, sphdata->flow);
    speed = len_v3(relative_vel);
    if (sim->courant_num < speed * dtime / sphdata->element_size)
        sim->courant_num = speed * dtime / sphdata->element_size;
}
/* Update time step size to suit current conditions. */
float update_timestep(ParticleSystem *psys, ParticleSimulationData *sim,
    float t_frac)
{
    if (sim->courant_num == 0.0f)
        psys->dt_frac = 1.0f;
    else
        psys->dt_frac *= (psys->part->courant_target / sim->courant_num);
    CLAMP(psys->dt_frac, MIN_TIMESTEP, 1.0f);

    /* Sync with frame end if it's close. */
    if (t_frac == 1.0f)
        return psys->dt_frac;
    else if (t_frac + (psys->dt_frac * TIMESTEP_EXPANSION_TOLERANCE) >= 1.0f)
        return 1.0f - t_frac;
    else
        return psys->dt_frac;
}

/************************************************/
/*          System Core                         */
/************************************************/
/* unbaked particles are calculated dynamically */
static void dynamics_step(ParticleSimulationData *sim, float cfra)
{
    ParticleSystem *psys = sim->psys;
    ParticleSettings *part=psys->part;
    BoidBrainData bbd;
    ParticleTexture ptex;
    PARTICLE_P;
    float timestep;
    /* frame & time changes */
    float dfra, dtime;
    float birthtime, dietime;

    /* where have we gone in time since last time */
    dfra= cfra - psys->cfra;

    timestep = psys_get_timestep(sim);
    dtime= dfra*timestep;

    if(dfra < 0.0f) {
        LOOP_EXISTING_PARTICLES {
            psys_get_texture(sim, pa, &ptex, PAMAP_SIZE, cfra);
            pa->size = part->size*ptex.size;
            if(part->randsize > 0.0f)
                pa->size *= 1.0f - part->randsize * PSYS_FRAND(p + 1);

            reset_particle(sim, pa, dtime, cfra);
        }
        return;
    }

    BLI_srandom(31415926 + (int)cfra + psys->seed);

    psys_update_effectors(sim);

    if(part->type != PART_HAIR)
        sim->colliders = get_collider_cache(sim->scene, sim->ob, NULL);

    /* initialize physics type specific stuff */
    switch(part->phystype) {
        case PART_PHYS_BOIDS:
        {
            ParticleTarget *pt = psys->targets.first;
            bbd.sim = sim;
            bbd.part = part;
            bbd.cfra = cfra;
            bbd.dfra = dfra;
            bbd.timestep = timestep;

            psys_update_particle_tree(psys, cfra);

            boids_precalc_rules(part, cfra);

            for(; pt; pt=pt->next) {
                if(pt->ob)
                    psys_update_particle_tree(BLI_findlink(&pt->ob->particlesystem, pt->psys-1), cfra);
            }
            break;
        }
        case PART_PHYS_FLUID:
        {
            ParticleTarget *pt = psys->targets.first;
            psys_update_particle_bvhtree(psys, cfra);
            
            for(; pt; pt=pt->next) {  /* Updating others systems particle tree for fluid-fluid interaction */
                if(pt->ob)
                    psys_update_particle_bvhtree(BLI_findlink(&pt->ob->particlesystem, pt->psys-1), cfra);
            }
            break;
        }
    }
    /* initialize all particles for dynamics */
    LOOP_SHOWN_PARTICLES {
        copy_particle_key(&pa->prev_state,&pa->state,1);

        psys_get_texture(sim, pa, &ptex, PAMAP_SIZE, cfra);

        pa->size = part->size*ptex.size;
        if(part->randsize > 0.0f)
            pa->size *= 1.0f - part->randsize * PSYS_FRAND(p + 1);

        birthtime = pa->time;
        dietime = pa->dietime;

        /* store this, so we can do multiple loops over particles */
        pa->state.time = dfra;

        if(dietime <= cfra && psys->cfra < dietime){
            /* particle dies some time between this and last step */
            pa->state.time = dietime - ((birthtime > psys->cfra) ? birthtime : psys->cfra);
            pa->alive = PARS_DYING;
        }
        else if(birthtime <= cfra && birthtime >= psys->cfra){
            /* particle is born some time between this and last step*/
            reset_particle(sim, pa, dfra*timestep, cfra);
            pa->alive = PARS_ALIVE;
            pa->state.time = cfra - birthtime;
        }
        else if(dietime < cfra){
            /* nothing to be done when particle is dead */
        }

        /* only reset unborn particles if they're shown or if the particle is born soon*/
        if(pa->alive==PARS_UNBORN
            && (part->flag & PART_UNBORN || cfra + psys->pointcache->step > pa->time))
            reset_particle(sim, pa, dtime, cfra);
        else if(part->phystype == PART_PHYS_NO)
            reset_particle(sim, pa, dtime, cfra);

        if(ELEM(pa->alive, PARS_ALIVE, PARS_DYING)==0 || (pa->flag & (PARS_UNEXIST|PARS_NO_DISP)))
            pa->state.time = -1.f;
    }

    switch(part->phystype) {
        case PART_PHYS_NEWTON:
        {
            LOOP_DYNAMIC_PARTICLES {
                /* do global forces & effectors */
                basic_integrate(sim, p, pa->state.time, cfra);
    
                /* deflection */
                if(sim->colliders)
                    collision_check(sim, p, pa->state.time, cfra);

                /* rotations */
                basic_rotate(part, pa, pa->state.time, timestep);
            }
            break;
        }
        case PART_PHYS_BOIDS:
        {
            LOOP_DYNAMIC_PARTICLES {
                bbd.goal_ob = NULL;
                
                boid_brain(&bbd, p, pa);

                if(pa->alive != PARS_DYING) {
                    boid_body(&bbd, pa);

                    /* deflection */
                    if(sim->colliders)
                        collision_check(sim, p, pa->state.time, cfra);
                }
            }
            break;
        }
        case PART_PHYS_FLUID:
        {
            SPHData sphdata;
            sph_solver_init(sim, &sphdata);

            #pragma omp parallel for firstprivate (sphdata) private (pa) schedule(dynamic,5)
            LOOP_DYNAMIC_PARTICLES {
                /* do global forces & effectors */
                basic_integrate(sim, p, pa->state.time, cfra);

                /* actual fluids calculations */
                sph_integrate(sim, pa, pa->state.time, &sphdata);

                if(sim->colliders)
                    collision_check(sim, p, pa->state.time, cfra);
                
                /* SPH particles are not physical particles, just interpolation
                 * particles,  thus rotation has not a direct sense for them */
                basic_rotate(part, pa, pa->state.time, timestep);  

                #pragma omp critical
                if (part->time_flag & PART_TIME_AUTOSF)
                    update_courant_num(sim, pa, dtime, &sphdata);
            }

            sph_springs_modify(psys, timestep);

            sph_solver_finalise(&sphdata);
            break;
        }
    }

    /* finalize particle state and time after dynamics */
    LOOP_DYNAMIC_PARTICLES {
        if(pa->alive == PARS_DYING){
            pa->alive=PARS_DEAD;
            pa->state.time=pa->dietime;
        }
        else
            pa->state.time=cfra;
    }

    free_collider_cache(&sim->colliders);
}
static void update_children(ParticleSimulationData *sim)
{
    if((sim->psys->part->type == PART_HAIR) && (sim->psys->flag & PSYS_HAIR_DONE)==0)
    /* don't generate children while growing hair - waste of time */
        psys_free_children(sim->psys);
    else if(sim->psys->part->childtype) {
        if(sim->psys->totchild != get_psys_tot_child(sim->scene, sim->psys))
            distribute_particles(sim, PART_FROM_CHILD);
        else {
            /* Children are up to date, nothing to do. */
        }
    }
    else
        psys_free_children(sim->psys);
}
/* updates cached particles' alive & other flags etc..*/
static void cached_step(ParticleSimulationData *sim, float cfra)
{
    ParticleSystem *psys = sim->psys;
    ParticleSettings *part = psys->part;
    ParticleTexture ptex;
    PARTICLE_P;
    float disp, dietime;

    psys_update_effectors(sim);
    
    disp= (float)psys_get_current_display_percentage(psys)/100.0f;

    LOOP_PARTICLES {
        psys_get_texture(sim, pa, &ptex, PAMAP_SIZE, cfra);
        pa->size = part->size*ptex.size;
        if(part->randsize > 0.0f)
            pa->size *= 1.0f - part->randsize * PSYS_FRAND(p + 1);

        psys->lattice= psys_get_lattice(sim);

        dietime = pa->dietime;

        /* update alive status and push events */
        if(pa->time > cfra) {
            pa->alive = PARS_UNBORN;
            if(part->flag & PART_UNBORN && (psys->pointcache->flag & PTCACHE_EXTERNAL) == 0)
                reset_particle(sim, pa, 0.0f, cfra);
        }
        else if(dietime <= cfra)
            pa->alive = PARS_DEAD;
        else
            pa->alive = PARS_ALIVE;

        if(psys->lattice){
            end_latt_deform(psys->lattice);
            psys->lattice= NULL;
        }

        if(PSYS_FRAND(p) > disp)
            pa->flag |= PARS_NO_DISP;
        else
            pa->flag &= ~PARS_NO_DISP;
    }
}

static void particles_fluid_step(ParticleSimulationData *sim, int UNUSED(cfra))
{   
    ParticleSystem *psys = sim->psys;
    if(psys->particles){
        MEM_freeN(psys->particles);
        psys->particles = 0;
        psys->totpart = 0;
    }

    /* fluid sim particle import handling, actual loading of particles from file */
    #ifdef WITH_MOD_FLUID
    {
        FluidsimModifierData *fluidmd = (FluidsimModifierData *)modifiers_findByType(sim->ob, eModifierType_Fluidsim);
        
        if( fluidmd && fluidmd->fss) { 
            FluidsimSettings *fss= fluidmd->fss;
            ParticleSettings *part = psys->part;
            ParticleData *pa=NULL;
            char filename[256];
            char debugStrBuffer[256];
            int  curFrame = sim->scene->r.cfra -1; // warning - sync with derived mesh fsmesh loading
            int  p, j, totpart;
            int readMask, activeParts = 0, fileParts = 0;
            gzFile gzf;
    
// XXX          if(ob==G.obedit) // off...
//              return;

            // ok, start loading
            BLI_join_dirfile(filename, sizeof(filename), fss->surfdataPath, OB_FLUIDSIM_SURF_PARTICLES_FNAME);

            BLI_path_abs(filename, modifier_path_relbase(sim->ob));

            BLI_path_frame(filename, curFrame, 0); // fixed #frame-no 

            gzf = gzopen(filename, "rb");
            if (!gzf) {
                BLI_snprintf(debugStrBuffer, sizeof(debugStrBuffer),"readFsPartData::error - Unable to open file for reading '%s' \n", filename); 
                // XXX bad level call elbeemDebugOut(debugStrBuffer);
                return;
            }
    
            gzread(gzf, &totpart, sizeof(totpart));
            totpart = (G.rendering)?totpart:(part->disp*totpart)/100;
            
            part->totpart= totpart;
            part->sta=part->end = 1.0f;
            part->lifetime = sim->scene->r.efra + 1;
    
            /* allocate particles */
            realloc_particles(sim, part->totpart);
    
            // set up reading mask
            readMask = fss->typeFlags;
            
            for(p=0, pa=psys->particles; p<totpart; p++, pa++) {
                int ptype=0;
    
                gzread(gzf, &ptype, sizeof( ptype )); 
                if(ptype&readMask) {
                    activeParts++;
    
                    gzread(gzf, &(pa->size), sizeof( float )); 
    
                    pa->size /= 10.0f;
    
                    for(j=0; j<3; j++) {
                        float wrf;
                        gzread(gzf, &wrf, sizeof( wrf )); 
                        pa->state.co[j] = wrf;
                        //fprintf(stderr,"Rj%d ",j);
                    }
                    for(j=0; j<3; j++) {
                        float wrf;
                        gzread(gzf, &wrf, sizeof( wrf )); 
                        pa->state.vel[j] = wrf;
                    }
    
                    pa->state.ave[0] = pa->state.ave[1] = pa->state.ave[2] = 0.0f;
                    pa->state.rot[0] = 1.0;
                    pa->state.rot[1] = pa->state.rot[2] = pa->state.rot[3] = 0.0;
    
                    pa->time = 1.f;
                    pa->dietime = sim->scene->r.efra + 1;
                    pa->lifetime = sim->scene->r.efra;
                    pa->alive = PARS_ALIVE;
                    //if(a<25) fprintf(stderr,"FSPARTICLE debug set %s , a%d = %f,%f,%f , life=%f \n", filename, a, pa->co[0],pa->co[1],pa->co[2], pa->lifetime );
                } else {
                    // skip...
                    for(j=0; j<2*3+1; j++) {
                        float wrf; gzread(gzf, &wrf, sizeof( wrf )); 
                    }
                }
                fileParts++;
            }
            gzclose( gzf );
    
            totpart = psys->totpart = activeParts;
            BLI_snprintf(debugStrBuffer,sizeof(debugStrBuffer),"readFsPartData::done - particles:%d, active:%d, file:%d, mask:%d  \n", psys->totpart,activeParts,fileParts,readMask);
            // bad level call
            // XXX elbeemDebugOut(debugStrBuffer);
            
        } // fluid sim particles done
    }
    #endif // WITH_MOD_FLUID
}

static int emit_particles(ParticleSimulationData *sim, PTCacheID *pid, float UNUSED(cfra))
{
    ParticleSystem *psys = sim->psys;
    int oldtotpart = psys->totpart;
    int totpart = tot_particles(psys, pid);

    if(totpart != oldtotpart)
        realloc_particles(sim, totpart);

    return totpart - oldtotpart;
}

/* Calculates the next state for all particles of the system
 * In particles code most fra-ending are frames, time-ending are fra*timestep (seconds)
 * 1. Emit particles
 * 2. Check cache (if used) and return if frame is cached
 * 3. Do dynamics
 * 4. Save to cache */
static void system_step(ParticleSimulationData *sim, float cfra)
{
    ParticleSystem *psys = sim->psys;
    ParticleSettings *part = psys->part;
    PointCache *cache = psys->pointcache;
    PTCacheID ptcacheid, *pid = NULL;
    PARTICLE_P;
    float disp, cache_cfra = cfra; /*, *vg_vel= 0, *vg_tan= 0, *vg_rot= 0, *vg_size= 0; */
    int startframe = 0, endframe = 100, oldtotpart = 0;

    /* cache shouldn't be used for hair or "continue physics" */
    if(part->type != PART_HAIR && BKE_ptcache_get_continue_physics() == 0) {
        psys_clear_temp_pointcache(psys);

        /* set suitable cache range automatically */
        if((cache->flag & (PTCACHE_BAKING|PTCACHE_BAKED))==0)
            psys_get_pointcache_start_end(sim->scene, psys, &cache->startframe, &cache->endframe);

        pid = &ptcacheid;
        BKE_ptcache_id_from_particles(pid, sim->ob, psys);
        
        BKE_ptcache_id_time(pid, sim->scene, 0.0f, &startframe, &endframe, NULL);

        /* clear everythin on start frame */
        if(cfra == startframe) {
            BKE_ptcache_id_reset(sim->scene, pid, PTCACHE_RESET_OUTDATED);
            BKE_ptcache_validate(cache, startframe);
            cache->flag &= ~PTCACHE_REDO_NEEDED;
        }
        
        CLAMP(cache_cfra, startframe, endframe);
    }

/* 1. emit particles and redo particles if needed */
    oldtotpart = psys->totpart;
    if(emit_particles(sim, pid, cfra) || psys->recalc & PSYS_RECALC_RESET) {
        distribute_particles(sim, part->from);
        initialize_all_particles(sim);
        /* reset only just created particles (on startframe all particles are recreated) */
        reset_all_particles(sim, 0.0, cfra, oldtotpart);

        if (psys->fluid_springs) {
            MEM_freeN(psys->fluid_springs);
            psys->fluid_springs = NULL;
        }

        psys->tot_fluidsprings = psys->alloc_fluidsprings = 0;

        /* flag for possible explode modifiers after this system */
        sim->psmd->flag |= eParticleSystemFlag_Pars;

        BKE_ptcache_id_clear(pid, PTCACHE_CLEAR_AFTER, cfra);
    }

/* 2. try to read from the cache */
    if(pid) {
        int cache_result = BKE_ptcache_read(pid, cache_cfra);

        if(ELEM(cache_result, PTCACHE_READ_EXACT, PTCACHE_READ_INTERPOLATED)) {
            cached_step(sim, cfra);
            update_children(sim);
            psys_update_path_cache(sim, cfra);

            BKE_ptcache_validate(cache, (int)cache_cfra);

            if(cache_result == PTCACHE_READ_INTERPOLATED && cache->flag & PTCACHE_REDO_NEEDED)
                BKE_ptcache_write(pid, (int)cache_cfra);

            return;
        }
        /* Cache is supposed to be baked, but no data was found so bail out */
        else if(cache->flag & PTCACHE_BAKED) {
            psys_reset(psys, PSYS_RESET_CACHE_MISS);
            return;
        }
        else if(cache_result == PTCACHE_READ_OLD) {
            psys->cfra = (float)cache->simframe;
            cached_step(sim, psys->cfra);
        }

        /* if on second frame, write cache for first frame */
        if(psys->cfra == startframe && (cache->flag & PTCACHE_OUTDATED || cache->last_exact==0))
            BKE_ptcache_write(pid, startframe);
    }
    else
        BKE_ptcache_invalidate(cache);

/* 3. do dynamics */
    /* set particles to be not calculated TODO: can't work with pointcache */
    disp= (float)psys_get_current_display_percentage(psys)/100.0f;

    LOOP_PARTICLES {
        if(PSYS_FRAND(p) > disp)
            pa->flag |= PARS_NO_DISP;
        else
            pa->flag &= ~PARS_NO_DISP;
    }

    if(psys->totpart) {
        int dframe, totframesback = 0;
        float t_frac, dt_frac;

        /* handle negative frame start at the first frame by doing
         * all the steps before the first frame */
        if((int)cfra == startframe && part->sta < startframe)
            totframesback = (startframe - (int)part->sta);

        if (!(part->time_flag & PART_TIME_AUTOSF)) {
            /* Constant time step */
            psys->dt_frac = 1.0f / (float) (part->subframes + 1);
        } else if ((int)cfra == startframe) {
            /* Variable time step; use a very conservative value at the start.
             * If it doesn't need to be so small, it will quickly grow. */
            psys->dt_frac = 1.0;
        } else if (psys->dt_frac < MIN_TIMESTEP) {
            psys->dt_frac = MIN_TIMESTEP;
        }

        for(dframe=-totframesback; dframe<=0; dframe++) {
            /* simulate each subframe */
            dt_frac = psys->dt_frac;
            for (t_frac = dt_frac; t_frac <= 1.0f; t_frac += dt_frac) {
                sim->courant_num = 0.0f;
                dynamics_step(sim, cfra+dframe+t_frac - 1.f);
                psys->cfra = cfra+dframe+t_frac - 1.f;
#if 0
                printf("%f,%f,%f,%f\n", cfra+dframe+t_frac - 1.f, t_frac, dt_frac, sim->courant_num);
#endif
                if (part->time_flag & PART_TIME_AUTOSF)
                    dt_frac = update_timestep(psys, sim, t_frac);
            }
        }
    }
    
/* 4. only write cache starting from second frame */
    if(pid) {
        BKE_ptcache_validate(cache, (int)cache_cfra);
        if((int)cache_cfra != startframe)
            BKE_ptcache_write(pid, (int)cache_cfra);
    }

    update_children(sim);

/* cleanup */
    if(psys->lattice){
        end_latt_deform(psys->lattice);
        psys->lattice= NULL;
    }
}

/* system type has changed so set sensible defaults and clear non applicable flags */
static void psys_changed_type(ParticleSimulationData *sim)
{
    ParticleSettings *part = sim->psys->part;
    PTCacheID pid;

    BKE_ptcache_id_from_particles(&pid, sim->ob, sim->psys);

    if(part->phystype != PART_PHYS_KEYED)
        sim->psys->flag &= ~PSYS_KEYED;

    if(part->type == PART_HAIR) {
        if(ELEM4(part->ren_as, PART_DRAW_NOT, PART_DRAW_PATH, PART_DRAW_OB, PART_DRAW_GR)==0)
            part->ren_as = PART_DRAW_PATH;

        if(part->distr == PART_DISTR_GRID)
            part->distr = PART_DISTR_JIT;

        if(ELEM3(part->draw_as, PART_DRAW_NOT, PART_DRAW_REND, PART_DRAW_PATH)==0)
            part->draw_as = PART_DRAW_REND;

        CLAMP(part->path_start, 0.0f, 100.0f);
        CLAMP(part->path_end, 0.0f, 100.0f);

        BKE_ptcache_id_clear(&pid, PTCACHE_CLEAR_ALL, 0);
    }
    else {
        free_hair(sim->ob, sim->psys, 1);

        CLAMP(part->path_start, 0.0f, MAX2(100.0f, part->end + part->lifetime));
        CLAMP(part->path_end, 0.0f, MAX2(100.0f, part->end + part->lifetime));
    }

    psys_reset(sim->psys, PSYS_RESET_ALL);
}
void psys_check_boid_data(ParticleSystem *psys)
{
        BoidParticle *bpa;
        PARTICLE_P;

        pa = psys->particles;

        if(!pa)
            return;

        if(psys->part && psys->part->phystype==PART_PHYS_BOIDS) {
            if(!pa->boid) {
                bpa = MEM_callocN(psys->totpart * sizeof(BoidParticle), "Boid Data");

                LOOP_PARTICLES
                    pa->boid = bpa++;
            }
        }
        else if(pa->boid){
            MEM_freeN(pa->boid);
            LOOP_PARTICLES
                pa->boid = NULL;
        }
}

static void fluid_default_settings(ParticleSettings *part)
{
    SPHFluidSettings *fluid = part->fluid;

    fluid->spring_k = 0.f;
    fluid->plasticity_constant = 0.1f;
    fluid->yield_ratio = 0.1f;
    fluid->rest_length = 1.f;
    fluid->viscosity_omega = 2.f;
    fluid->viscosity_beta = 0.1f;
    fluid->stiffness_k = 1.f;
    fluid->stiffness_knear = 1.f;
    fluid->rest_density = 1.f;
    fluid->buoyancy = 0.f;
    fluid->radius = 1.f;
    fluid->flag |= SPH_FAC_REPULSION|SPH_FAC_DENSITY|SPH_FAC_RADIUS|SPH_FAC_VISCOSITY|SPH_FAC_REST_LENGTH;
}

static void psys_prepare_physics(ParticleSimulationData *sim)
{
    ParticleSettings *part = sim->psys->part;

    if(ELEM(part->phystype, PART_PHYS_NO, PART_PHYS_KEYED)) {
        PTCacheID pid;
        BKE_ptcache_id_from_particles(&pid, sim->ob, sim->psys);
        BKE_ptcache_id_clear(&pid, PTCACHE_CLEAR_ALL, 0);
    }
    else {
        free_keyed_keys(sim->psys);
        sim->psys->flag &= ~PSYS_KEYED;
    }

    if(part->phystype == PART_PHYS_BOIDS && part->boids == NULL) {
        BoidState *state;

        part->boids = MEM_callocN(sizeof(BoidSettings), "Boid Settings");
        boid_default_settings(part->boids);

        state = boid_new_state(part->boids);
        BLI_addtail(&state->rules, boid_new_rule(eBoidRuleType_Separate));
        BLI_addtail(&state->rules, boid_new_rule(eBoidRuleType_Flock));

        ((BoidRule*)state->rules.first)->flag |= BOIDRULE_CURRENT;

        state->flag |= BOIDSTATE_CURRENT;
        BLI_addtail(&part->boids->states, state);
    }
    else if(part->phystype == PART_PHYS_FLUID && part->fluid == NULL) {
        part->fluid = MEM_callocN(sizeof(SPHFluidSettings), "SPH Fluid Settings");
        fluid_default_settings(part);
    }

    psys_check_boid_data(sim->psys);
}
static int hair_needs_recalc(ParticleSystem *psys)
{
    if(!(psys->flag & PSYS_EDITED) && (!psys->edit || !psys->edit->edited) &&
        ((psys->flag & PSYS_HAIR_DONE)==0 || psys->recalc & PSYS_RECALC_RESET || (psys->part->flag & PART_HAIR_REGROW && !psys->edit))) {
        return 1;
    }

    return 0;
}

/* main particle update call, checks that things are ok on the large scale and
 * then advances in to actual particle calculations depending on particle type */
void particle_system_update(Scene *scene, Object *ob, ParticleSystem *psys)
{
    ParticleSimulationData sim= {0};
    ParticleSettings *part = psys->part;
    float cfra;

    /* drawdata is outdated after ANY change */
    if(psys->pdd) psys->pdd->flag &= ~PARTICLE_DRAW_DATA_UPDATED;

    if(!psys_check_enabled(ob, psys))
        return;

    cfra= BKE_curframe(scene);

    sim.scene= scene;
    sim.ob= ob;
    sim.psys= psys;
    sim.psmd= psys_get_modifier(ob, psys);

    /* system was already updated from modifier stack */
    if(sim.psmd->flag & eParticleSystemFlag_psys_updated) {
        sim.psmd->flag &= ~eParticleSystemFlag_psys_updated;
        /* make sure it really was updated to cfra */
        if(psys->cfra == cfra)
            return;
    }

    if(!sim.psmd->dm)
        return;

    /* execute drivers only, as animation has already been done */
    BKE_animsys_evaluate_animdata(scene, &part->id, part->adt, cfra, ADT_RECALC_DRIVERS);

    if(psys->recalc & PSYS_RECALC_TYPE)
        psys_changed_type(&sim);

    if(psys->recalc & PSYS_RECALC_RESET)
        psys->totunexist = 0;

    /* setup necessary physics type dependent additional data if it doesn't yet exist */
    psys_prepare_physics(&sim);

    switch(part->type) {
        case PART_HAIR:
        {
            /* nothing to do so bail out early */
            if(psys->totpart == 0 && part->totpart == 0) {
                psys_free_path_cache(psys, NULL);
                free_hair(ob, psys, 0);
            }
            /* (re-)create hair */
            else if(hair_needs_recalc(psys)) {
                float hcfra=0.0f;
                int i, recalc = psys->recalc;

                free_hair(ob, psys, 0);

                if(psys->edit && psys->free_edit) {
                    psys->free_edit(psys->edit);
                    psys->edit = NULL;
                    psys->free_edit = NULL;
                }

                /* first step is negative so particles get killed and reset */
                psys->cfra= 1.0f;

                for(i=0; i<=part->hair_step; i++){
                    hcfra=100.0f*(float)i/(float)psys->part->hair_step;
                    if((part->flag & PART_HAIR_REGROW)==0)
                        BKE_animsys_evaluate_animdata(scene, &part->id, part->adt, hcfra, ADT_RECALC_ANIM);
                    system_step(&sim, hcfra);
                    psys->cfra = hcfra;
                    psys->recalc = 0;
                    save_hair(&sim, hcfra);
                }

                psys->flag |= PSYS_HAIR_DONE;
                psys->recalc = recalc;
            }
            else if(psys->flag & PSYS_EDITED)
                psys->flag |= PSYS_HAIR_DONE;

            if(psys->flag & PSYS_HAIR_DONE)
                hair_step(&sim, cfra);
            break;
        }
        case PART_FLUID:
        {
            particles_fluid_step(&sim, (int)cfra);
            break;
        }
        default:
        {
            switch(part->phystype) {
                case PART_PHYS_NO:
                case PART_PHYS_KEYED:
                {
                    PARTICLE_P;
                    float disp = (float)psys_get_current_display_percentage(psys)/100.0f;

                    /* Particles without dynamics haven't been reset yet because they don't use pointcache */
                    if(psys->recalc & PSYS_RECALC_RESET)
                        psys_reset(psys, PSYS_RESET_ALL);

                    if(emit_particles(&sim, NULL, cfra) || (psys->recalc & PSYS_RECALC_RESET)) {
                        free_keyed_keys(psys);
                        distribute_particles(&sim, part->from);
                        initialize_all_particles(&sim);

                        /* flag for possible explode modifiers after this system */
                        sim.psmd->flag |= eParticleSystemFlag_Pars;
                    }

                    LOOP_EXISTING_PARTICLES {
                        pa->size = part->size;
                        if(part->randsize > 0.0f)
                            pa->size *= 1.0f - part->randsize * PSYS_FRAND(p + 1);

                        reset_particle(&sim, pa, 0.0, cfra);

                        if(PSYS_FRAND(p) > disp)
                            pa->flag |= PARS_NO_DISP;
                        else
                            pa->flag &= ~PARS_NO_DISP;
                    }

                    if(part->phystype == PART_PHYS_KEYED) {
                        psys_count_keyed_targets(&sim);
                        set_keyed_keys(&sim);
                        psys_update_path_cache(&sim,(int)cfra);
                    }
                    break;
                }
                default:
                {
                    /* the main dynamic particle system step */
                    system_step(&sim, cfra);
                    break;
                }
            }
            break;
        }
    }

    if(psys->cfra < cfra) {
        /* make sure emitter is left at correct time (particle emission can change this) */
        while(ob) {
            BKE_animsys_evaluate_animdata(scene, &ob->id, ob->adt, cfra, ADT_RECALC_ANIM);
            ob = ob->parent;
        }
        ob = sim.ob;
        where_is_object_time(scene, ob, cfra);
    }

    psys->cfra = cfra;
    psys->recalc = 0;

    /* save matrix for duplicators, at rendertime the actual dupliobject's matrix is used so don't update! */
    if(psys->renderdata==0)
        invert_m4_m4(psys->imat, ob->obmat);
}