forked from bartvdbraak/blender
Brecht Van Lommel
fe222643b4
This is done using the existing Emission node and closure (we may add a volume emission node, not clear yet if it will be needed). Volume emission only supports indirect light sampling which means it's not very efficient to make small or far away bright light sources. Using direct light sampling and MIS would be tricky and probably won't be added anytime soon. Other renderers don't support this either as far as I know, lamps and ray visibility tricks may be used instead.
143 lines
3.9 KiB
C
143 lines
3.9 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 __VOLUME_H__
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#define __VOLUME_H__
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CCL_NAMESPACE_BEGIN
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/* HENYEY-GREENSTEIN CLOSURE */
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/* Given cosine between rays, return probability density that a photon bounces
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* to that direction. The g parameter controls how different it is from the
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* uniform sphere. g=0 uniform diffuse-like, g=1 close to sharp single ray. */
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ccl_device float single_peaked_henyey_greenstein(float cos_theta, float g)
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{
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if(fabsf(g) < 1e-3f)
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return M_1_PI_F * 0.25f;
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return ((1.0f - g * g) / safe_powf(1.0f + g * g - 2.0f * g * cos_theta, 1.5f)) * (M_1_PI_F * 0.25f);
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};
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ccl_device int volume_henyey_greenstein_setup(ShaderClosure *sc)
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{
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sc->type = CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID;
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/* clamp anisotropy to avoid delta function */
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sc->data0 = signf(sc->data0) * min(fabsf(sc->data0), 1.0f - 1e-3f);
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return SD_BSDF|SD_BSDF_HAS_EVAL|SD_VOLUME;
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}
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ccl_device float3 volume_henyey_greenstein_eval_phase(const ShaderClosure *sc, const float3 I, float3 omega_in, float *pdf)
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{
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float g = sc->data0;
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/* note that I points towards the viewer */
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float cos_theta = dot(-I, omega_in);
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*pdf = single_peaked_henyey_greenstein(cos_theta, g);
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return make_float3(*pdf, *pdf, *pdf);
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}
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ccl_device int volume_henyey_greenstein_sample(const ShaderClosure *sc, float3 I, float3 dIdx, float3 dIdy, float randu, float randv,
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float3 *eval, float3 *omega_in, float3 *domega_in_dx, float3 *domega_in_dy, float *pdf)
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{
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float g = sc->data0;
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float cos_phi, sin_phi, cos_theta;
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/* match pdf for small g */
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if(fabsf(g) < 1e-3f) {
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cos_theta = (1.0f - 2.0f * randu);
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}
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else {
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float k = (1.0f - g * g) / (1.0f - g + 2.0f * g * randu);
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cos_theta = (1.0f + g * g - k * k) / (2.0f * g);
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}
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float sin_theta = safe_sqrtf(1.0f - cos_theta * cos_theta);
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float phi = M_2PI_F * randv;
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cos_phi = cosf(phi);
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sin_phi = sinf(phi);
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/* note that I points towards the viewer and so is used negated */
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float3 T, B;
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make_orthonormals(-I, &T, &B);
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*omega_in = sin_theta * cos_phi * T + sin_theta * sin_phi * B + cos_theta * (-I);
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*pdf = single_peaked_henyey_greenstein(cos_theta, g);
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*eval = make_float3(*pdf, *pdf, *pdf); /* perfect importance sampling */
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#ifdef __RAY_DIFFERENTIALS__
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/* todo: implement ray differential estimation */
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*domega_in_dx = make_float3(0.0f, 0.0f, 0.0f);
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*domega_in_dy = make_float3(0.0f, 0.0f, 0.0f);
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#endif
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return LABEL_VOLUME_SCATTER;
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}
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/* ABSORPTION VOLUME CLOSURE */
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ccl_device int volume_absorption_setup(ShaderClosure *sc)
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{
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sc->type = CLOSURE_VOLUME_ABSORPTION_ID;
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return SD_VOLUME;
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}
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/* VOLUME CLOSURE */
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ccl_device float3 volume_eval_phase(const ShaderClosure *sc, const float3 I, float3 omega_in, float *pdf)
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{
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float3 eval;
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switch(sc->type) {
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case CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID:
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eval = volume_henyey_greenstein_eval_phase(sc, I, omega_in, pdf);
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break;
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default:
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eval = make_float3(0.0f, 0.0f, 0.0f);
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break;
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}
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return eval;
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}
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ccl_device int volume_sample(const ShaderData *sd, const ShaderClosure *sc, float randu,
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float randv, float3 *eval, float3 *omega_in, differential3 *domega_in, float *pdf)
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{
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int label;
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switch(sc->type) {
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case CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID:
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label = volume_henyey_greenstein_sample(sc, sd->I, sd->dI.dx, sd->dI.dy, randu, randv, eval, omega_in, &domega_in->dx, &domega_in->dy, pdf);
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break;
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default:
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*eval = make_float3(0.0f, 0.0f, 0.0f);
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label = LABEL_NONE;
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break;
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}
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return label;
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}
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CCL_NAMESPACE_END
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#endif
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