Cycles: add build option to enable a debugging feature for MIS

This patch adds a CMake option "WITH_CYCLES_DEBUG" which builds cycles with
a feature that allows debugging/selecting the direct-light sampling strategy.
The same option may later be used to add other debugging features that could
affect performance in release builds.

The three options are:
* Forward path tracing (e.g., via BSDF or phase function)
* Next-event estimation
* Multiple importance sampling combination of the previous two methods

Such a feature is useful for debugging light different sampling, evaluation,
and pdf methods (e.g., for light sources and BSDFs).

Differential Revision: https://developer.blender.org/D13152

1 files changed, 14 insertions, 1 deletions

diff --git a/intern/cycles/kernel/types.h b/intern/cycles/kernel/types.h
index 74b34524786..e66c3fe49df 100644
--- a/intern/cycles/kernel/types.h
+++ b/intern/cycles/kernel/types.h
@@ -481,6 +481,16 @@ enum PanoramaType {
   PANORAMA_NUM_TYPES,
 };
 
+/* Direct Light Sampling */
+
+enum DirectLightSamplingType {
+  DIRECT_LIGHT_SAMPLING_MIS = 0,
+  DIRECT_LIGHT_SAMPLING_FORWARD = 1,
+  DIRECT_LIGHT_SAMPLING_NEE = 2,
+
+  DIRECT_LIGHT_SAMPLING_NUM,
+};
+
 /* Differential */
 
 typedef struct differential3 {
@@ -1193,8 +1203,11 @@ typedef struct KernelIntegrator {
   /* Closure filter. */
   int filter_closures;
 
+  /* MIS debuging */
+  int direct_light_sampling_type;
+
   /* padding */
-  int pad1, pad2, pad3;
+  int pad1, pad2;
 } KernelIntegrator;
 static_assert_align(KernelIntegrator, 16);