bsdf_ward.cpp

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/*
 * Adapted from Open Shading Language with this license:
 *
 * Copyright (c) 2009-2010 Sony Pictures Imageworks Inc., et al.
 * All Rights Reserved.
 *
 * Modifications Copyright 2011, Blender Foundation.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * * Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * * Neither the name of Sony Pictures Imageworks nor the names of its
 *   contributors may be used to endorse or promote products derived from
 *   this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <OpenImageIO/fmath.h>

#include <OSL/genclosure.h>

#include "osl_closures.h"

#include "util_math.h"

CCL_NAMESPACE_BEGIN

using namespace OSL;

// anisotropic ward - leaks energy at grazing angles
// see http://www.graphics.cornell.edu/~bjw/wardnotes.pdf 
class WardClosure : public BSDFClosure {
public:
    Vec3 m_N;
    Vec3 m_T;
    float m_ax, m_ay;
    WardClosure() : BSDFClosure(Labels::GLOSSY) { }

    void setup()
    {
        m_ax = clamp(m_ax, 1e-5f, 1.0f);
        m_ay = clamp(m_ay, 1e-5f, 1.0f);
    }

    bool mergeable (const ClosurePrimitive *other) const {
        const WardClosure *comp = (const WardClosure *)other;
        return m_N == comp->m_N && m_T == comp->m_T &&
            m_ax == comp->m_ax && m_ay == comp->m_ay &&
            BSDFClosure::mergeable(other);
    }

    size_t memsize () const { return sizeof(*this); }

    const char *name () const { return "ward"; }

    void print_on (std::ostream &out) const {
        out << name() << " ((";
        out << m_N[0] << ", " << m_N[1] << ", " << m_N[2] << "), (";
        out << m_T[0] << ", " << m_T[1] << ", " << m_T[2] << "), ";
        out << m_ax << ", " << m_ay << ")";
    }

    float albedo (const Vec3 &omega_out) const
    {
        return 1.0f;
    }

    Color3 eval_reflect (const Vec3 &omega_out, const Vec3 &omega_in, float& pdf) const
    {
        float cosNO = m_N.dot(omega_out);
        float cosNI = m_N.dot(omega_in);
        if (cosNI > 0 && cosNO > 0) {
            // get half vector and get x,y basis on the surface for anisotropy
            Vec3 H = omega_in + omega_out;
            H.normalize();  // normalize needed for pdf
            Vec3 X, Y;
            make_orthonormals(m_N, m_T, X, Y);
            // eq. 4
            float dotx = H.dot(X) / m_ax;
            float doty = H.dot(Y) / m_ay;
            float dotn = H.dot(m_N);
            float exp_arg = (dotx * dotx + doty * doty) / (dotn * dotn);
            float denom = (4 * (float) M_PI * m_ax * m_ay * sqrtf(cosNO * cosNI));
            float exp_val = expf(-exp_arg);
            float out = cosNI * exp_val / denom;
            float oh = H.dot(omega_out);
            denom = 4 * (float) M_PI * m_ax * m_ay * oh * dotn * dotn * dotn;
            pdf = exp_val / denom;
            return Color3 (out, out, out);
        }
        return Color3 (0, 0, 0);
    }

    Color3 eval_transmit (const Vec3 &omega_out, const Vec3 &omega_in, float& pdf) const
    {
        return Color3 (0, 0, 0);
    }

    ustring sample (const Vec3 &Ng,
                 const Vec3 &omega_out, const Vec3 &domega_out_dx, const Vec3 &domega_out_dy,
                 float randu, float randv,
                 Vec3 &omega_in, Vec3 &domega_in_dx, Vec3 &domega_in_dy,
                 float &pdf, Color3 &eval) const
    {
        float cosNO = m_N.dot(omega_out);
        if (cosNO > 0) {
            // get x,y basis on the surface for anisotropy
            Vec3 X, Y;
            make_orthonormals(m_N, m_T, X, Y);
            // generate random angles for the half vector
            // eq. 7 (taking care around discontinuities to keep
            //        output angle in the right quadrant)
            // we take advantage of cos(atan(x)) == 1/sqrt(1+x^2)
            //                  and sin(atan(x)) == x/sqrt(1+x^2)
            float alphaRatio = m_ay / m_ax;
            float cosPhi, sinPhi;
            if (randu < 0.25f) {
                float val = 4 * randu;
                float tanPhi = alphaRatio * tanf((float) M_PI_2 * val);
                cosPhi = 1 / sqrtf(1 + tanPhi * tanPhi);
                sinPhi = tanPhi * cosPhi;
            } else if (randu < 0.5) {
                float val = 1 - 4 * (0.5f - randu);
                float tanPhi = alphaRatio * tanf((float) M_PI_2 * val);
                // phi = (float) M_PI - phi;
                cosPhi = -1 / sqrtf(1 + tanPhi * tanPhi);
                sinPhi = -tanPhi * cosPhi;
            } else if (randu < 0.75f) {
                float val = 4 * (randu - 0.5f);
                float tanPhi = alphaRatio * tanf((float) M_PI_2 * val);
                //phi = (float) M_PI + phi;
                cosPhi = -1 / sqrtf(1 + tanPhi * tanPhi);
                sinPhi = tanPhi * cosPhi;
            } else {
                float val = 1 - 4 * (1 - randu);
                float tanPhi = alphaRatio * tanf((float) M_PI_2 * val);
                // phi = 2 * (float) M_PI - phi;
                cosPhi = 1 / sqrtf(1 + tanPhi * tanPhi);
                sinPhi = -tanPhi * cosPhi;
            }
            // eq. 6
            // we take advantage of cos(atan(x)) == 1/sqrt(1+x^2)
            //                  and sin(atan(x)) == x/sqrt(1+x^2)
            float thetaDenom = (cosPhi * cosPhi) / (m_ax * m_ax) + (sinPhi * sinPhi) / (m_ay * m_ay);
            float tanTheta2 = -logf(1 - randv) / thetaDenom;
            float cosTheta  = 1 / sqrtf(1 + tanTheta2);
            float sinTheta  = cosTheta * sqrtf(tanTheta2);

            Vec3 h; // already normalized becaused expressed from spherical coordinates
            h.x = sinTheta * cosPhi;
            h.y = sinTheta * sinPhi;
            h.z = cosTheta;
            // compute terms that are easier in local space
            float dotx = h.x / m_ax;
            float doty = h.y / m_ay;
            float dotn = h.z;
            // transform to world space
            h = h.x * X + h.y * Y + h.z * m_N;
            // generate the final sample
            float oh = h.dot(omega_out);
            omega_in.x = 2 * oh * h.x - omega_out.x;
            omega_in.y = 2 * oh * h.y - omega_out.y;
            omega_in.z = 2 * oh * h.z - omega_out.z;
            if (Ng.dot(omega_in) > 0) {
                float cosNI = m_N.dot(omega_in);
                if (cosNI > 0) {
                    // eq. 9
                    float exp_arg = (dotx * dotx + doty * doty) / (dotn * dotn);
                    float denom = 4 * (float) M_PI * m_ax * m_ay * oh * dotn * dotn * dotn;
                    pdf = expf(-exp_arg) / denom;
                    // compiler will reuse expressions already computed
                    denom = (4 * (float) M_PI * m_ax * m_ay * sqrtf(cosNO * cosNI));
                    float power = cosNI * expf(-exp_arg) / denom;
                    eval.setValue(power, power, power);
                    domega_in_dx = (2 * m_N.dot(domega_out_dx)) * m_N - domega_out_dx;
                    domega_in_dy = (2 * m_N.dot(domega_out_dy)) * m_N - domega_out_dy;

                    /* disabled for now - gives texture filtering problems */
#if 0
                    // Since there is some blur to this reflection, make the
                    // derivatives a bit bigger. In theory this varies with the
                    // roughness but the exact relationship is complex and
                    // requires more ops than are practical.
                    domega_in_dx *= 10;
                    domega_in_dy *= 10;
#endif
                }
            }
        }
        return Labels::REFLECT;
    }
};



ClosureParam bsdf_ward_params[] = {
    CLOSURE_VECTOR_PARAM(WardClosure, m_N),
    CLOSURE_VECTOR_PARAM(WardClosure, m_T),
    CLOSURE_FLOAT_PARAM (WardClosure, m_ax),
    CLOSURE_FLOAT_PARAM (WardClosure, m_ay),
    CLOSURE_STRING_KEYPARAM("label"),
    CLOSURE_FINISH_PARAM(WardClosure) };

CLOSURE_PREPARE(bsdf_ward_prepare, WardClosure)

CCL_NAMESPACE_END