forked from bartvdbraak/blender
617 lines
20 KiB
C
617 lines
20 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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CCL_NAMESPACE_BEGIN
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typedef enum VolumeIntegrateResult {
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VOLUME_PATH_SCATTERED = 0,
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VOLUME_PATH_ATTENUATED = 1,
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VOLUME_PATH_MISSED = 2
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} VolumeIntegrateResult;
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/* Volume shader properties
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*
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* extinction coefficient = absorption coefficient + scattering coefficient
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* sigma_t = sigma_a + sigma_s */
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typedef struct VolumeShaderCoefficients {
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float3 sigma_a;
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float3 sigma_s;
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float3 emission;
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} VolumeShaderCoefficients;
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/* evaluate shader to get extinction coefficient at P */
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ccl_device bool volume_shader_extinction_sample(KernelGlobals *kg, ShaderData *sd, PathState *state, float3 P, float3 *extinction)
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{
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sd->P = P;
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shader_eval_volume(kg, sd, state->volume_stack, PATH_RAY_SHADOW, SHADER_CONTEXT_SHADOW);
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if(!(sd->flag & (SD_ABSORPTION|SD_SCATTER)))
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return false;
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float3 sigma_t = make_float3(0.0f, 0.0f, 0.0f);
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for(int i = 0; i < sd->num_closure; i++) {
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const ShaderClosure *sc = &sd->closure[i];
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if(CLOSURE_IS_VOLUME(sc->type))
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sigma_t += sc->weight;
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}
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*extinction = sigma_t;
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return true;
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}
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/* evaluate shader to get absorption, scattering and emission at P */
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ccl_device bool volume_shader_sample(KernelGlobals *kg, ShaderData *sd, PathState *state, float3 P, VolumeShaderCoefficients *coeff)
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{
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sd->P = P;
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shader_eval_volume(kg, sd, state->volume_stack, state->flag, SHADER_CONTEXT_VOLUME);
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if(!(sd->flag & (SD_ABSORPTION|SD_SCATTER|SD_EMISSION)))
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return false;
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coeff->sigma_a = make_float3(0.0f, 0.0f, 0.0f);
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coeff->sigma_s = make_float3(0.0f, 0.0f, 0.0f);
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coeff->emission = make_float3(0.0f, 0.0f, 0.0f);
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for(int i = 0; i < sd->num_closure; i++) {
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const ShaderClosure *sc = &sd->closure[i];
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if(sc->type == CLOSURE_VOLUME_ABSORPTION_ID)
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coeff->sigma_a += sc->weight;
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else if(sc->type == CLOSURE_EMISSION_ID)
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coeff->emission += sc->weight;
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else if(CLOSURE_IS_VOLUME(sc->type))
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coeff->sigma_s += sc->weight;
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}
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/* when at the max number of bounces, treat scattering as absorption */
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if(sd->flag & SD_SCATTER) {
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if(state->volume_bounce >= kernel_data.integrator.max_volume_bounce) {
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coeff->sigma_a += coeff->sigma_s;
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coeff->sigma_s = make_float3(0.0f, 0.0f, 0.0f);
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sd->flag &= ~SD_SCATTER;
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sd->flag |= SD_ABSORPTION;
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}
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}
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return true;
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}
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ccl_device float3 volume_color_attenuation(float3 sigma, float t)
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{
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return make_float3(expf(-sigma.x * t), expf(-sigma.y * t), expf(-sigma.z * t));
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}
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ccl_device bool volume_stack_is_heterogeneous(KernelGlobals *kg, VolumeStack *stack)
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{
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for(int i = 0; stack[i].shader != SHADER_NO_ID; i++) {
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int shader_flag = kernel_tex_fetch(__shader_flag, (stack[i].shader & SHADER_MASK)*2);
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if(shader_flag & SD_HETEROGENEOUS_VOLUME)
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return true;
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}
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return false;
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}
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/* Volume Shadows
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*
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* These functions are used to attenuate shadow rays to lights. Both absorption
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* and scattering will block light, represented by the extinction coefficient. */
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/* homogeneous volume: assume shader evaluation at the starts gives
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* the extinction coefficient for the entire line segment */
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ccl_device void kernel_volume_shadow_homogeneous(KernelGlobals *kg, PathState *state, Ray *ray, ShaderData *sd, float3 *throughput)
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{
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float3 sigma_t;
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if(volume_shader_extinction_sample(kg, sd, state, ray->P, &sigma_t))
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*throughput *= volume_color_attenuation(sigma_t, ray->t);
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}
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/* heterogeneous volume: integrate stepping through the volume until we
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* reach the end, get absorbed entirely, or run out of iterations */
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ccl_device void kernel_volume_shadow_heterogeneous(KernelGlobals *kg, PathState *state, Ray *ray, ShaderData *sd, float3 *throughput)
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{
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float3 tp = *throughput;
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const float tp_eps = 1e-10f; /* todo: this is likely not the right value */
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/* prepare for stepping */
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int max_steps = kernel_data.integrator.volume_max_steps;
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float step = kernel_data.integrator.volume_step_size;
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float random_jitter_offset = lcg_step_float(&state->rng_congruential) * step;
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/* compute extinction at the start */
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float t = 0.0f;
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float3 P = ray->P;
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float3 sigma_t;
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if(!volume_shader_extinction_sample(kg, sd, state, P, &sigma_t))
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sigma_t = make_float3(0.0f, 0.0f, 0.0f);
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for(int i = 0; i < max_steps; i++) {
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/* advance to new position */
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float new_t = min(ray->t, t + random_jitter_offset + i * step);
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float3 new_P = ray->P + ray->D * new_t;
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float3 new_sigma_t;
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/* compute attenuation over segment */
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if(volume_shader_extinction_sample(kg, sd, state, new_P, &new_sigma_t)) {
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/* todo: we could avoid computing expf() for each step by summing,
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* because exp(a)*exp(b) = exp(a+b), but we still want a quick
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* tp_eps check too */
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tp *= volume_color_attenuation(0.5f*(sigma_t + new_sigma_t), new_t - t);
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/* stop if nearly all light blocked */
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if(tp.x < tp_eps && tp.y < tp_eps && tp.z < tp_eps)
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break;
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sigma_t = new_sigma_t;
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}
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else {
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/* skip empty space */
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sigma_t = make_float3(0.0f, 0.0f, 0.0f);
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}
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/* stop if at the end of the volume */
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t = new_t;
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if(t == ray->t)
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break;
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}
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*throughput = tp;
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}
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/* get the volume attenuation over line segment defined by ray, with the
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* assumption that there are no surfaces blocking light between the endpoints */
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ccl_device_noinline void kernel_volume_shadow(KernelGlobals *kg, PathState *state, Ray *ray, float3 *throughput)
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{
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ShaderData sd;
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shader_setup_from_volume(kg, &sd, ray, state->bounce);
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if(volume_stack_is_heterogeneous(kg, state->volume_stack))
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kernel_volume_shadow_heterogeneous(kg, state, ray, &sd, throughput);
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else
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kernel_volume_shadow_homogeneous(kg, state, ray, &sd, throughput);
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}
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/* Volume Path */
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/* homogeneous volume: assume shader evaluation at the start gives
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* the volume shading coefficient for the entire line segment */
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ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(KernelGlobals *kg,
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PathState *state, Ray *ray, ShaderData *sd, PathRadiance *L, float3 *throughput,
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RNG *rng)
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{
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VolumeShaderCoefficients coeff;
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if(!volume_shader_sample(kg, sd, state, ray->P, &coeff))
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return VOLUME_PATH_MISSED;
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int closure_flag = sd->flag;
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float t = ray->t;
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float3 new_tp;
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float3 transmittance;
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/* randomly scatter, and if we do t is shortened */
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if(closure_flag & SD_SCATTER) {
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float3 sigma_t = coeff.sigma_a + coeff.sigma_s;
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/* set up variables for sampling */
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float rphase = path_state_rng_1D(kg, rng, state, PRNG_PHASE);
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int channel = (int)(rphase*3.0f);
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sd->randb_closure = rphase*3.0f - channel;
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/* pick random color channel, we use the Veach one-sample
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* model with balance heuristic for the channels */
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float sample_sigma_t;
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if(channel == 0)
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sample_sigma_t = sigma_t.x;
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else if(channel == 1)
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sample_sigma_t = sigma_t.y;
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else
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sample_sigma_t = sigma_t.z;
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/* distance sampling */
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if(kernel_data.integrator.volume_homogeneous_sampling == 0 || !kernel_data.integrator.num_all_lights) {
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/* xi is [0, 1[ so log(0) should never happen, division by zero is
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* avoided because sample_sigma_t > 0 when SD_SCATTER is set */
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float xi = path_state_rng_1D(kg, rng, state, PRNG_SCATTER_DISTANCE);
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float sample_t = min(t, -logf(1.0f - xi)/sample_sigma_t);
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transmittance = volume_color_attenuation(sigma_t, sample_t);
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if(sample_t < t) {
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float pdf = dot(sigma_t, transmittance);
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new_tp = *throughput * coeff.sigma_s * transmittance * (3.0f / pdf);
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t = sample_t;
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}
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else {
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float pdf = (transmittance.x + transmittance.y + transmittance.z);
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new_tp = *throughput * transmittance * (3.0f / pdf);
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}
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}
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/* equi-angular sampling */
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else {
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/* decide if we are going to scatter or not, based on sigma_t. this
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* is not ideal, instead we should perhaps split the path here and
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* do both, and at least add multiple importance sampling */
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float xi = path_state_rng_1D(kg, rng, state, PRNG_SCATTER_DISTANCE);
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float sample_transmittance = expf(-sample_sigma_t * t);
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if(xi < sample_transmittance) {
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/* no scattering */
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transmittance = volume_color_attenuation(sigma_t, t);
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float pdf = (transmittance.x + transmittance.y + transmittance.z);
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new_tp = *throughput * transmittance * (3.0f / pdf);
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}
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else {
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/* rescale random number so we can reuse it */
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xi = (xi - sample_transmittance)/(1.0f - sample_transmittance);
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/* equi-angular scattering somewhere on segment 0..t */
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/* see "Importance Sampling Techniques for Path Tracing in Participating Media" */
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/* light RNGs */
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float light_t = path_state_rng_1D(kg, rng, state, PRNG_LIGHT);
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float light_u, light_v;
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path_state_rng_2D(kg, rng, state, PRNG_LIGHT_U, &light_u, &light_v);
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/* light sample */
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LightSample ls;
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light_sample(kg, light_t, light_u, light_v, ray->time, ray->P, &ls);
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if(ls.pdf == 0.0f)
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return VOLUME_PATH_MISSED;
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/* sampling */
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float delta = dot((ls.P - ray->P) , ray->D);
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float D = sqrtf(len_squared(ls.P - ray->P) - delta * delta);
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float theta_a = -atan2f(delta, D);
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float theta_b = atan2f(t - delta, D);
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float t_ = D * tan((xi * theta_b) + (1 - xi) * theta_a);
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float pdf = D / ((theta_b - theta_a) * (D * D + t_ * t_));
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float sample_t = min(t, delta + t_);
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transmittance = volume_color_attenuation(sigma_t, sample_t);
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new_tp = *throughput * coeff.sigma_s * transmittance / ((1.0f - sample_transmittance) * pdf);
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t = sample_t;
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}
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}
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}
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else if(closure_flag & SD_ABSORPTION) {
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/* absorption only, no sampling needed */
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transmittance = volume_color_attenuation(coeff.sigma_a, t);
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new_tp = *throughput * transmittance;
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}
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/* integrate emission attenuated by extinction
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* integral E * exp(-sigma_t * t) from 0 to t = E * (1 - exp(-sigma_t * t))/sigma_t
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* this goes to E * t as sigma_t goes to zero
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*
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* todo: we should use an epsilon to avoid precision issues near zero sigma_t */
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if(closure_flag & SD_EMISSION) {
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float3 emission = coeff.emission;
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if(closure_flag & SD_ABSORPTION) {
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float3 sigma_t = coeff.sigma_a + coeff.sigma_s;
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emission.x *= (sigma_t.x > 0.0f)? (1.0f - transmittance.x)/sigma_t.x: t;
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emission.y *= (sigma_t.y > 0.0f)? (1.0f - transmittance.y)/sigma_t.y: t;
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emission.z *= (sigma_t.z > 0.0f)? (1.0f - transmittance.z)/sigma_t.z: t;
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}
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else
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emission *= t;
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path_radiance_accum_emission(L, *throughput, emission, state->bounce);
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}
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/* modify throughput */
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if(closure_flag & (SD_ABSORPTION|SD_SCATTER)) {
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*throughput = new_tp;
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/* prepare to scatter to new direction */
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if(t < ray->t) {
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/* adjust throughput and move to new location */
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sd->P = ray->P + t*ray->D;
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return VOLUME_PATH_SCATTERED;
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}
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}
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return VOLUME_PATH_ATTENUATED;
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}
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/* heterogeneous volume: integrate stepping through the volume until we
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* reach the end, get absorbed entirely, or run out of iterations */
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ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlobals *kg,
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PathState *state, Ray *ray, ShaderData *sd, PathRadiance *L, float3 *throughput, RNG *rng)
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{
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VolumeShaderCoefficients coeff;
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float3 tp = *throughput;
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const float tp_eps = 1e-10f; /* todo: this is likely not the right value */
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/* prepare for stepping */
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int max_steps = kernel_data.integrator.volume_max_steps;
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float step = kernel_data.integrator.volume_step_size;
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float random_jitter_offset = lcg_step_float(&state->rng_congruential) * step;
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/* compute coefficients at the start */
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float t = 0.0f;
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float3 P = ray->P;
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if(!volume_shader_sample(kg, sd, state, P, &coeff)) {
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coeff.sigma_a = make_float3(0.0f, 0.0f, 0.0f);
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coeff.sigma_s = make_float3(0.0f, 0.0f, 0.0f);
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coeff.emission = make_float3(0.0f, 0.0f, 0.0f);
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}
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/* accumulate these values so we can use a single stratified number to sample */
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float3 accum_transmittance = make_float3(1.0f, 1.0f, 1.0f);
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float3 accum_sigma_t = make_float3(0.0f, 0.0f, 0.0f);
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float3 accum_sigma_s = make_float3(0.0f, 0.0f, 0.0f);
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/* cache some constant variables */
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float nlogxi;
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int channel = -1;
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bool has_scatter = false;
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for(int i = 0; i < max_steps; i++) {
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/* advance to new position */
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float new_t = min(ray->t, t + random_jitter_offset + i * step);
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float3 new_P = ray->P + ray->D * new_t;
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VolumeShaderCoefficients new_coeff;
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/* compute segment */
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if(volume_shader_sample(kg, sd, state, new_P, &new_coeff)) {
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int closure_flag = sd->flag;
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float dt = new_t - t;
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float3 new_tp;
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float3 transmittance;
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bool scatter = false;
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/* randomly scatter, and if we do dt and new_t are shortened */
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if((closure_flag & SD_SCATTER) || (has_scatter && (closure_flag & SD_ABSORPTION))) {
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has_scatter = true;
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/* average sigma_t and sigma_s over segment */
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float3 last_sigma_t = coeff.sigma_a + coeff.sigma_s;
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float3 new_sigma_t = new_coeff.sigma_a + new_coeff.sigma_s;
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float3 sigma_t = 0.5f*(last_sigma_t + new_sigma_t);
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float3 sigma_s = 0.5f*(coeff.sigma_s + new_coeff.sigma_s);
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/* lazily set up variables for sampling */
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if(channel == -1) {
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float xi = path_state_rng_1D(kg, rng, state, PRNG_SCATTER_DISTANCE);
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nlogxi = -logf(1.0f - xi);
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float rphase = path_state_rng_1D(kg, rng, state, PRNG_PHASE);
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channel = (int)(rphase*3.0f);
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sd->randb_closure = rphase*3.0f - channel;
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}
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/* pick random color channel, we use the Veach one-sample
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* model with balance heuristic for the channels */
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float sample_sigma_t;
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if(channel == 0)
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sample_sigma_t = accum_sigma_t.x + dt*sigma_t.x;
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else if(channel == 1)
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sample_sigma_t = accum_sigma_t.y + dt*sigma_t.y;
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else
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sample_sigma_t = accum_sigma_t.z + dt*sigma_t.z;
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if(nlogxi < sample_sigma_t) {
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/* compute sampling distance */
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sample_sigma_t /= new_t;
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new_t = nlogxi/sample_sigma_t;
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dt = new_t - t;
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transmittance = volume_color_attenuation(sigma_t, dt);
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accum_transmittance *= transmittance;
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accum_sigma_t = (accum_sigma_t + dt*sigma_t)/new_t;
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accum_sigma_s = (accum_sigma_s + dt*sigma_s)/new_t;
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/* todo: it's not clear to me that this is correct if we move
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* through a color volume, needs verification */
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float pdf = dot(accum_sigma_t, accum_transmittance);
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new_tp = tp * accum_sigma_s * transmittance * (3.0f / pdf);
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scatter = true;
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}
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else {
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transmittance = volume_color_attenuation(sigma_t, dt);
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accum_transmittance *= transmittance;
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accum_sigma_t += dt*sigma_t;
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accum_sigma_s += dt*sigma_s;
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new_tp = tp * transmittance;
|
|
}
|
|
}
|
|
else if(closure_flag & SD_ABSORPTION) {
|
|
/* absorption only, no sampling needed */
|
|
float3 sigma_a = 0.5f*(coeff.sigma_a + new_coeff.sigma_a);
|
|
transmittance = volume_color_attenuation(sigma_a, dt);
|
|
|
|
accum_transmittance *= transmittance;
|
|
accum_sigma_t += dt*sigma_a;
|
|
|
|
new_tp = tp * transmittance;
|
|
|
|
/* todo: we could avoid computing expf() for each step by summing,
|
|
* because exp(a)*exp(b) = exp(a+b), but we still want a quick
|
|
* tp_eps check too */
|
|
}
|
|
|
|
/* integrate emission attenuated by absorption
|
|
* integral E * exp(-sigma_t * t) from 0 to t = E * (1 - exp(-sigma_t * t))/sigma_t
|
|
* this goes to E * t as sigma_t goes to zero
|
|
*
|
|
* todo: we should use an epsilon to avoid precision issues near zero sigma_t */
|
|
if(closure_flag & SD_EMISSION) {
|
|
float3 emission = 0.5f*(coeff.emission + new_coeff.emission);
|
|
|
|
if(closure_flag & SD_ABSORPTION) {
|
|
float3 sigma_t = 0.5f*(coeff.sigma_a + coeff.sigma_s + new_coeff.sigma_a + new_coeff.sigma_s);
|
|
|
|
emission.x *= (sigma_t.x > 0.0f)? (1.0f - transmittance.x)/sigma_t.x: dt;
|
|
emission.y *= (sigma_t.y > 0.0f)? (1.0f - transmittance.y)/sigma_t.y: dt;
|
|
emission.z *= (sigma_t.z > 0.0f)? (1.0f - transmittance.z)/sigma_t.z: dt;
|
|
}
|
|
else
|
|
emission *= dt;
|
|
|
|
path_radiance_accum_emission(L, tp, emission, state->bounce);
|
|
}
|
|
|
|
/* modify throughput */
|
|
if(closure_flag & (SD_ABSORPTION|SD_SCATTER)) {
|
|
tp = new_tp;
|
|
|
|
/* stop if nearly all light blocked */
|
|
if(tp.x < tp_eps && tp.y < tp_eps && tp.z < tp_eps) {
|
|
tp = make_float3(0.0f, 0.0f, 0.0f);
|
|
break;
|
|
}
|
|
|
|
/* prepare to scatter to new direction */
|
|
if(scatter) {
|
|
/* adjust throughput and move to new location */
|
|
sd->P = ray->P + new_t*ray->D;
|
|
*throughput = tp;
|
|
|
|
return VOLUME_PATH_SCATTERED;
|
|
}
|
|
}
|
|
|
|
coeff = new_coeff;
|
|
}
|
|
else {
|
|
/* skip empty space */
|
|
coeff.sigma_a = make_float3(0.0f, 0.0f, 0.0f);
|
|
coeff.sigma_s = make_float3(0.0f, 0.0f, 0.0f);
|
|
coeff.emission = make_float3(0.0f, 0.0f, 0.0f);
|
|
}
|
|
|
|
/* stop if at the end of the volume */
|
|
t = new_t;
|
|
if(t == ray->t)
|
|
break;
|
|
}
|
|
|
|
/* include pdf for volumes with scattering */
|
|
if(has_scatter) {
|
|
float pdf = (accum_transmittance.x + accum_transmittance.y + accum_transmittance.z);
|
|
if(pdf > 0.0f)
|
|
tp *= (3.0f/pdf);
|
|
}
|
|
|
|
*throughput = tp;
|
|
|
|
return VOLUME_PATH_ATTENUATED;
|
|
}
|
|
|
|
/* get the volume attenuation and emission over line segment defined by
|
|
* ray, with the assumption that there are no surfaces blocking light
|
|
* between the endpoints */
|
|
ccl_device_noinline VolumeIntegrateResult kernel_volume_integrate(KernelGlobals *kg,
|
|
PathState *state, ShaderData *sd, Ray *ray, PathRadiance *L, float3 *throughput, RNG *rng)
|
|
{
|
|
/* workaround to fix correlation bug in T38710, can find better solution
|
|
* in random number generator later, for now this is done here to not impact
|
|
* performance of rendering without volumes */
|
|
RNG tmp_rng = cmj_hash(*rng, state->rng_offset);
|
|
|
|
shader_setup_from_volume(kg, sd, ray, state->bounce);
|
|
|
|
if(volume_stack_is_heterogeneous(kg, state->volume_stack))
|
|
return kernel_volume_integrate_heterogeneous(kg, state, ray, sd, L, throughput, &tmp_rng);
|
|
else
|
|
return kernel_volume_integrate_homogeneous(kg, state, ray, sd, L, throughput, &tmp_rng);
|
|
}
|
|
|
|
/* Volume Stack
|
|
*
|
|
* This is an array of object/shared ID's that the current segment of the path
|
|
* is inside of. */
|
|
|
|
ccl_device void kernel_volume_stack_init(KernelGlobals *kg, VolumeStack *stack)
|
|
{
|
|
/* todo: this assumes camera is always in air, need to detect when it isn't */
|
|
if(kernel_data.background.volume_shader == SHADER_NO_ID) {
|
|
stack[0].shader = SHADER_NO_ID;
|
|
}
|
|
else {
|
|
stack[0].shader = kernel_data.background.volume_shader;
|
|
stack[0].object = ~0;
|
|
stack[1].shader = SHADER_NO_ID;
|
|
}
|
|
}
|
|
|
|
ccl_device void kernel_volume_stack_enter_exit(KernelGlobals *kg, ShaderData *sd, VolumeStack *stack)
|
|
{
|
|
/* todo: we should have some way for objects to indicate if they want the
|
|
* world shader to work inside them. excluding it by default is problematic
|
|
* because non-volume objects can't be assumed to be closed manifolds */
|
|
|
|
if(!(sd->flag & SD_HAS_VOLUME))
|
|
return;
|
|
|
|
if(sd->flag & SD_BACKFACING) {
|
|
/* exit volume object: remove from stack */
|
|
for(int i = 0; stack[i].shader != SHADER_NO_ID; i++) {
|
|
if(stack[i].object == sd->object) {
|
|
/* shift back next stack entries */
|
|
do {
|
|
stack[i] = stack[i+1];
|
|
i++;
|
|
}
|
|
while(stack[i].shader != SHADER_NO_ID);
|
|
|
|
return;
|
|
}
|
|
}
|
|
}
|
|
else {
|
|
/* enter volume object: add to stack */
|
|
int i;
|
|
|
|
for(i = 0; stack[i].shader != SHADER_NO_ID; i++) {
|
|
/* already in the stack? then we have nothing to do */
|
|
if(stack[i].object == sd->object)
|
|
return;
|
|
}
|
|
|
|
/* if we exceed the stack limit, ignore */
|
|
if(i >= VOLUME_STACK_SIZE-1)
|
|
return;
|
|
|
|
/* add to the end of the stack */
|
|
stack[i].shader = sd->shader;
|
|
stack[i].object = sd->object;
|
|
stack[i+1].shader = SHADER_NO_ID;
|
|
}
|
|
}
|
|
|
|
CCL_NAMESPACE_END
|
|
|