Cycles: volume light sampling

* Volume multiple importace sampling support to combine equiangular and distance
  sampling, for both homogeneous and heterogeneous volumes.

* Branched path "Sample All Direct Lights" and "Sample All Indirect Lights" now
  apply to volumes as well as surfaces.

Implementation note:

For simplicity this is all done with decoupled ray marching, the only case we do
not use decoupled is for distance only sampling with one light sample. The
homogeneous case should still compile on the GPU because it only requires fixed
size storage, but the heterogeneous case will be trickier to get working.

1 files changed, 14 insertions, 3 deletions

diff --git a/intern/cycles/render/integrator.cpp b/intern/cycles/render/integrator.cpp
index 051ba1baf3a..ee3419b055c 100644
--- a/intern/cycles/render/integrator.cpp
+++ b/intern/cycles/render/integrator.cpp
@@ -101,7 +101,11 @@ void Integrator::device_update(Device *device, DeviceScene *dscene, Scene *scene
 	if(!transparent_shadows)
 		kintegrator->transparent_shadows = false;
 
-	kintegrator->volume_homogeneous_sampling = volume_homogeneous_sampling;
+	if(kintegrator->num_all_lights > 0)
+		kintegrator->volume_homogeneous_sampling = volume_homogeneous_sampling;
+	else
+		kintegrator->volume_homogeneous_sampling = 0;
+
 	kintegrator->volume_max_steps = volume_max_steps;
 	kintegrator->volume_step_size = volume_step_size;
 
@@ -125,8 +129,15 @@ void Integrator::device_update(Device *device, DeviceScene *dscene, Scene *scene
 	kintegrator->mesh_light_samples = mesh_light_samples;
 	kintegrator->subsurface_samples = subsurface_samples;
 	kintegrator->volume_samples = volume_samples;
-	kintegrator->sample_all_lights_direct = sample_all_lights_direct;
-	kintegrator->sample_all_lights_indirect = sample_all_lights_indirect;
+
+	if(method == BRANCHED_PATH) {
+		kintegrator->sample_all_lights_direct = sample_all_lights_direct;
+		kintegrator->sample_all_lights_indirect = sample_all_lights_indirect;
+	}
+	else {
+		kintegrator->sample_all_lights_direct = false;
+		kintegrator->sample_all_lights_indirect = false;
+	}
 
 	kintegrator->sampling_pattern = sampling_pattern;
 	kintegrator->aa_samples = aa_samples;