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, 1 insertions, 1 deletions

diff --git a/intern/cycles/kernel/integrator/shade_light.h b/intern/cycles/kernel/integrator/shade_light.h
index 5abe9e98abc..97ca430752c 100644
--- a/intern/cycles/kernel/integrator/shade_light.h
+++ b/intern/cycles/kernel/integrator/shade_light.h
@@ -84,7 +84,7 @@ ccl_device_inline void integrate_light(KernelGlobals kg,
     /* multiple importance sampling, get regular light pdf,
      * and compute weight with respect to BSDF pdf */
     const float mis_ray_pdf = INTEGRATOR_STATE(state, path, mis_ray_pdf);
-    const float mis_weight = power_heuristic(mis_ray_pdf, ls.pdf);
+    const float mis_weight = light_sample_mis_weight_forward(kg, mis_ray_pdf, ls.pdf);
     light_eval *= mis_weight;
   }