forked from bartvdbraak/blender
ee36e75b85
This was already mixed a bit, but the dot belongs there.
249 lines
6.2 KiB
C
249 lines
6.2 KiB
C
/*
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* Copyright 2011-2013 Blender Foundation
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef __KERNEL_BSSRDF_H__
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#define __KERNEL_BSSRDF_H__
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CCL_NAMESPACE_BEGIN
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ccl_device int bssrdf_setup(ShaderClosure *sc, ClosureType type)
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{
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if(sc->data0 < BSSRDF_MIN_RADIUS) {
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/* revert to diffuse BSDF if radius too small */
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sc->data0 = 0.0f;
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sc->data1 = 0.0f;
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int flag = bsdf_diffuse_setup(sc);
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sc->type = CLOSURE_BSDF_BSSRDF_ID;
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return flag;
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}
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else {
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sc->data1 = clamp(sc->data1, 0.0f, 1.0f); /* texture blur */
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sc->T.x = clamp(sc->T.x, 0.0f, 1.0f); /* sharpness */
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sc->type = type;
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return SD_BSDF|SD_BSDF_HAS_EVAL|SD_BSSRDF;
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}
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}
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/* Planar Truncated Gaussian
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*
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* Note how this is different from the typical gaussian, this one integrates
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* to 1 over the plane (where you get an extra 2*pi*x factor). We are lucky
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* that integrating x*exp(-x) gives a nice closed form solution. */
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/* paper suggests 1/12.46 which is much too small, suspect it's *12.46 */
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#define GAUSS_TRUNCATE 12.46f
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ccl_device float bssrdf_gaussian_eval(ShaderClosure *sc, float r)
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{
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/* integrate (2*pi*r * exp(-r*r/(2*v)))/(2*pi*v)) from 0 to Rm
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* = 1 - exp(-Rm*Rm/(2*v)) */
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const float v = sc->data0*sc->data0*(0.25f*0.25f);
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const float Rm = sqrtf(v*GAUSS_TRUNCATE);
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if(r >= Rm)
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return 0.0f;
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return expf(-r*r/(2.0f*v))/(2.0f*M_PI_F*v);
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}
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ccl_device float bssrdf_gaussian_pdf(ShaderClosure *sc, float r)
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{
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/* 1.0 - expf(-Rm*Rm/(2*v)) simplified */
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const float area_truncated = 1.0f - expf(-0.5f*GAUSS_TRUNCATE);
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return bssrdf_gaussian_eval(sc, r) * (1.0f/(area_truncated));
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}
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ccl_device void bssrdf_gaussian_sample(ShaderClosure *sc, float xi, float *r, float *h)
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{
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/* xi = integrate (2*pi*r * exp(-r*r/(2*v)))/(2*pi*v)) = -exp(-r^2/(2*v))
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* r = sqrt(-2*v*logf(xi)) */
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const float v = sc->data0*sc->data0*(0.25f*0.25f);
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const float Rm = sqrtf(v*GAUSS_TRUNCATE);
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/* 1.0 - expf(-Rm*Rm/(2*v)) simplified */
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const float area_truncated = 1.0f - expf(-0.5f*GAUSS_TRUNCATE);
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/* r(xi) */
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const float r_squared = -2.0f*v*logf(1.0f - xi*area_truncated);
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*r = sqrtf(r_squared);
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/* h^2 + r^2 = Rm^2 */
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*h = sqrtf(Rm*Rm - r_squared);
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}
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/* Planar Cubic BSSRDF falloff
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*
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* This is basically (Rm - x)^3, with some factors to normalize it. For sampling
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* we integrate 2*pi*x * (Rm - x)^3, which gives us a quintic equation that as
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* far as I can tell has no closed form solution. So we get an iterative solution
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* instead with newton-raphson. */
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ccl_device float bssrdf_cubic_eval(ShaderClosure *sc, float r)
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{
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const float sharpness = sc->T.x;
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if(sharpness == 0.0f) {
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const float Rm = sc->data0;
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if(r >= Rm)
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return 0.0f;
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/* integrate (2*pi*r * 10*(R - r)^3)/(pi * R^5) from 0 to R = 1 */
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const float Rm5 = (Rm*Rm) * (Rm*Rm) * Rm;
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const float f = Rm - r;
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const float num = f*f*f;
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return (10.0f * num) / (Rm5 * M_PI_F);
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}
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else {
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float Rm = sc->data0*(1.0f + sharpness);
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if(r >= Rm)
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return 0.0f;
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/* custom variation with extra sharpness, to match the previous code */
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const float y = 1.0f/(1.0f + sharpness);
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float Rmy, ry, ryinv;
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if(sharpness == 1.0f) {
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Rmy = sqrtf(Rm);
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ry = sqrtf(r);
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ryinv = (ry > 0.0f)? 1.0f/ry: 0.0f;
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}
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else {
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Rmy = powf(Rm, y);
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ry = powf(r, y);
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ryinv = (r > 0.0f)? powf(r, 2.0f*y - 2.0f): 0.0f;
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}
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const float Rmy5 = (Rmy*Rmy) * (Rmy*Rmy) * Rmy;
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const float f = Rmy - ry;
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const float num = f*(f*f)*(y*ryinv);
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return (10.0f * num) / (Rmy5 * M_PI_F);
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}
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}
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ccl_device float bssrdf_cubic_pdf(ShaderClosure *sc, float r)
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{
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return bssrdf_cubic_eval(sc, r);
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}
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/* solve 10x^2 - 20x^3 + 15x^4 - 4x^5 - xi == 0 */
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ccl_device float bssrdf_cubic_quintic_root_find(float xi)
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{
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/* newton-raphson iteration, usually succeeds in 2-4 iterations, except
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* outside 0.02 ... 0.98 where it can go up to 10, so overall performance
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* should not be too bad */
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const float tolerance = 1e-6f;
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const int max_iteration_count = 10;
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float x = 0.25f;
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int i;
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for (i = 0; i < max_iteration_count; i++) {
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float x2 = x*x;
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float x3 = x2*x;
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float nx = (1.0f - x);
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float f = 10.0f*x2 - 20.0f*x3 + 15.0f*x2*x2 - 4.0f*x2*x3 - xi;
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float f_ = 20.0f*(x*nx)*(nx*nx);
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if(fabsf(f) < tolerance || f_ == 0.0f)
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break;
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x = clamp(x - f/f_, 0.0f, 1.0f);
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}
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return x;
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}
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ccl_device void bssrdf_cubic_sample(ShaderClosure *sc, float xi, float *r, float *h)
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{
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float Rm = sc->data0;
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float r_ = bssrdf_cubic_quintic_root_find(xi);
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const float sharpness = sc->T.x;
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if(sharpness != 0.0f) {
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r_ = powf(r_, 1.0f + sharpness);
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Rm *= (1.0f + sharpness);
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}
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r_ *= Rm;
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*r = r_;
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/* h^2 + r^2 = Rm^2 */
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*h = sqrtf(Rm*Rm - r_*r_);
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}
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/* None BSSRDF falloff
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*
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* Samples distributed over disk with no falloff, for reference. */
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ccl_device float bssrdf_none_eval(ShaderClosure *sc, float r)
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{
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const float Rm = sc->data0;
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return (r < Rm)? 1.0f: 0.0f;
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}
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ccl_device float bssrdf_none_pdf(ShaderClosure *sc, float r)
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{
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/* integrate (2*pi*r)/(pi*Rm*Rm) from 0 to Rm = 1 */
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const float Rm = sc->data0;
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const float area = (M_PI_F*Rm*Rm);
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return bssrdf_none_eval(sc, r) / area;
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}
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ccl_device void bssrdf_none_sample(ShaderClosure *sc, float xi, float *r, float *h)
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{
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/* xi = integrate (2*pi*r)/(pi*Rm*Rm) = r^2/Rm^2
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* r = sqrt(xi)*Rm */
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const float Rm = sc->data0;
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const float r_ = sqrtf(xi)*Rm;
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*r = r_;
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/* h^2 + r^2 = Rm^2 */
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*h = sqrtf(Rm*Rm - r_*r_);
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}
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/* Generic */
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ccl_device void bssrdf_sample(ShaderClosure *sc, float xi, float *r, float *h)
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{
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if(sc->type == CLOSURE_BSSRDF_CUBIC_ID)
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bssrdf_cubic_sample(sc, xi, r, h);
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else
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bssrdf_gaussian_sample(sc, xi, r, h);
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}
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ccl_device float bssrdf_pdf(ShaderClosure *sc, float r)
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{
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if(sc->type == CLOSURE_BSSRDF_CUBIC_ID)
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return bssrdf_cubic_pdf(sc, r);
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else
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return bssrdf_gaussian_pdf(sc, r);
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}
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CCL_NAMESPACE_END
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#endif /* __KERNEL_BSSRDF_H__ */
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