Cycles: Add build option to enable a debugging feature for MIS
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Authored by Sebastian Herholz (sherholz) on Nov 9 2021, 10:33 AM.

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Brecht Van Lommel (brecht)
Sergey Sharybin (sergey)

Commits

rC087ae0778667: Add build option to enable a debugging feature for MIS
rBd9bc8f189cc3: Cycles: add build option to enable a debugging feature for MIS

Summary

This patch adds a CMake option "WITH_CYCLES_MIS_DEBUG" which builds cycles with a feature that allows debugging/selecting the direct-light sampling strategy.
The three options are:
fwd: forward path tracing (e.g., via BSDF or phase function)
nee: next-event estimation
mis: a 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).
The following example shows the classroom scene ideally all images should look the same:

This figure visualizes multiple problems with the light sources (e.g., nee and the ceiling over the lamps)

Via Python it is possible to select the direct light sampling method via:
scene.cycles.direct_light_sampling_type = "nee"

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Event Timeline

Sebastian Herholz (sherholz) requested review of this revision.Nov 9 2021, 10:33 AM

Sebastian Herholz (sherholz) created this revision.

Sebastian Herholz (sherholz) added a reviewer: Sergey Sharybin (sergey).

Sebastian Herholz (sherholz) edited the summary of this revision. (Show Details)Nov 9 2021, 10:37 AM

Thomas Dinges (dingto) added a subscriber: Thomas Dinges (dingto).Nov 9 2021, 11:45 AM

Thanks! Looks like a useful feature for debugging.

CMakeLists.txt
414	Can you rename this to `WITH_CYCLES_DEBUG`? I'd like to use to potentially add more options.
intern/cycles/blender/addon/properties.py
222–224	To follow naming conventions, can you change it to: ('MULTIPLE_IMPORTANCE_SAMPLING', "Multiple Importance Sampling", "Multiple importance sampling is used to combine direct light contributions from next-event estimation and forward path tracing", 0), ('FORWARD_PATH_TRACING', "Forward Path Tracing", "Direct light contributions are only sampled using forward path tracing", 1), ('NEXT_EVENT_ESTIMATION', "Next-Event Estimation", "Direct light contributions are only sampled using next-event estimation", 2),
426	typo "distriubtion", but this description seems like it should be changed.
intern/cycles/kernel/integrator/shade_background.h
84–94	This logic is repeated a few times, I think it would make sense to add a `float light_sample_mis_weight(KernelGlobals kg, const float forward_pdf, float nee_pdf)` utility function for this in `kernel/light/sample.h`.
intern/cycles/kernel/types.h
485–489	DIRECT_LIGHT_SAMPLING_MIS = 0, DIRECT_LIGHT_SAMPLING_FORWARD = 1, DIRECT_LIGHT_SAMPLING_NEE = 2, DIRECT_LIGHT_SAMPLING_NUM,
intern/cycles/scene/integrator.cpp
57–59	direct_light_sampling_type_enum.insert("multiple_importance_sampling", DLS_TYPE_MIS); direct_light_sampling_type_enum.insert("forward_path_tracing", DLS_TYPE_FWD); direct_light_sampling_type_enum.insert("next_event_estimation", DLS_TYPE_NEE);