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, 12 insertions, 6 deletions

diff --git a/intern/cycles/kernel/kernel_random.h b/intern/cycles/kernel/kernel_random.h
index ac04b3168a1..236f74c0a82 100644
--- a/intern/cycles/kernel/kernel_random.h
+++ b/intern/cycles/kernel/kernel_random.h
@@ -261,12 +261,12 @@ ccl_device uint lcg_init(uint seed)
  * For branches in the path we must be careful not to reuse the same number
  * in a sequence and offset accordingly. */
 
-ccl_device_inline float path_state_rng_1D(KernelGlobals *kg, RNG *rng, PathState *state, int dimension)
+ccl_device_inline float path_state_rng_1D(KernelGlobals *kg, RNG *rng, const PathState *state, int dimension)
 {
 	return path_rng_1D(kg, rng, state->sample, state->num_samples, state->rng_offset + dimension);
 }
 
-ccl_device_inline float path_state_rng_1D_for_decision(KernelGlobals *kg, RNG *rng, PathState *state, int dimension)
+ccl_device_inline float path_state_rng_1D_for_decision(KernelGlobals *kg, RNG *rng, const PathState *state, int dimension)
 {
 	/* the rng_offset is not increased for transparent bounces. if we do then
 	 * fully transparent objects can become subtly visible by the different
@@ -279,17 +279,23 @@ ccl_device_inline float path_state_rng_1D_for_decision(KernelGlobals *kg, RNG *r
 	return path_rng_1D(kg, rng, state->sample, state->num_samples, rng_offset + dimension);
 }
 
-ccl_device_inline void path_state_rng_2D(KernelGlobals *kg, RNG *rng, PathState *state, int dimension, float *fx, float *fy)
+ccl_device_inline void path_state_rng_2D(KernelGlobals *kg, RNG *rng, const PathState *state, int dimension, float *fx, float *fy)
 {
 	path_rng_2D(kg, rng, state->sample, state->num_samples, state->rng_offset + dimension, fx, fy);
 }
 
-ccl_device_inline float path_branched_rng_1D(KernelGlobals *kg, RNG *rng, PathState *state, int branch, int num_branches, int dimension)
+ccl_device_inline float path_branched_rng_1D(KernelGlobals *kg, RNG *rng, const PathState *state, int branch, int num_branches, int dimension)
 {
 	return path_rng_1D(kg, rng, state->sample*num_branches + branch, state->num_samples*num_branches, state->rng_offset + dimension);
 }
 
-ccl_device_inline void path_branched_rng_2D(KernelGlobals *kg, RNG *rng, PathState *state, int branch, int num_branches, int dimension, float *fx, float *fy)
+ccl_device_inline float path_branched_rng_1D_for_decision(KernelGlobals *kg, RNG *rng, const PathState *state, int branch, int num_branches, int dimension)
+{
+	int rng_offset = state->rng_offset + state->transparent_bounce*PRNG_BOUNCE_NUM;
+	return path_rng_1D(kg, rng, state->sample*num_branches + branch, state->num_samples*num_branches, rng_offset + dimension);
+}
+
+ccl_device_inline void path_branched_rng_2D(KernelGlobals *kg, RNG *rng, const PathState *state, int branch, int num_branches, int dimension, float *fx, float *fy)
 {
 	path_rng_2D(kg, rng, state->sample*num_branches + branch, state->num_samples*num_branches, state->rng_offset + dimension, fx, fy);
 }
@@ -303,7 +309,7 @@ ccl_device_inline void path_state_branch(PathState *state, int branch, int num_b
 	state->num_samples = state->num_samples*num_branches;
 }
 
-ccl_device_inline uint lcg_state_init(RNG *rng, PathState *state, uint scramble)
+ccl_device_inline uint lcg_state_init(RNG *rng, const PathState *state, uint scramble)
 {
 	return lcg_init(*rng + state->rng_offset + state->sample*scramble);
 }