Cycles: add Path Guiding on CPU through Intel OpenPGL

This adds path guiding features into Cycles by integrating Intel's Open Path
Guiding Library. It can be enabled in the Sampling > Path Guiding panel in the
render properties.

This feature helps reduce noise in scenes where finding a path to light is
difficult for regular path tracing.

The current implementation supports guiding directional sampling decisions on
surfaces, when the material contains a least one diffuse component, and in
volumes with isotropic and anisotropic Henyey-Greenstein phase functions.

On surfaces, the guided sampling decision is proportional to the product of
the incident radiance and the normal-oriented cosine lobe and in volumes it
is proportional to the product of the incident radiance and the phase function.

The incident radiance field of a scene is learned and updated during rendering
after each per-frame rendering iteration/progression.

At the moment, path guiding is only supported by the CPU backend. Support for
GPU backends will be added in future versions of OpenPGL.

Ref T92571

Differential Revision: https://developer.blender.org/D15286

1 files changed, 16 insertions, 3 deletions

diff --git a/intern/cycles/kernel/device/cpu/globals.h b/intern/cycles/kernel/device/cpu/globals.h
index 309afae412e..f7f1a36b2a7 100644
--- a/intern/cycles/kernel/device/cpu/globals.h
+++ b/intern/cycles/kernel/device/cpu/globals.h
@@ -9,6 +9,8 @@
 #include "kernel/types.h"
 #include "kernel/util/profiling.h"
 
+#include "util/guiding.h"
+
 CCL_NAMESPACE_BEGIN
 
 /* On the CPU, we pass along the struct KernelGlobals to nearly everywhere in
@@ -43,9 +45,20 @@ typedef struct KernelGlobalsCPU {
 #ifdef __OSL__
   /* On the CPU, we also have the OSL globals here. Most data structures are shared
    * with SVM, the difference is in the shaders and object/mesh attributes. */
-  OSLGlobals *osl;
-  OSLShadingSystem *osl_ss;
-  OSLThreadData *osl_tdata;
+  OSLGlobals *osl = nullptr;
+  OSLShadingSystem *osl_ss = nullptr;
+  OSLThreadData *osl_tdata = nullptr;
+#endif
+
+#ifdef __PATH_GUIDING__
+  /* Pointers to global data structures. */
+  openpgl::cpp::SampleStorage *opgl_sample_data_storage = nullptr;
+  openpgl::cpp::Field *opgl_guiding_field = nullptr;
+
+  /* Local data structures owned by the thread. */
+  openpgl::cpp::PathSegmentStorage *opgl_path_segment_storage = nullptr;
+  openpgl::cpp::SurfaceSamplingDistribution *opgl_surface_sampling_distribution = nullptr;
+  openpgl::cpp::VolumeSamplingDistribution *opgl_volume_sampling_distribution = nullptr;
 #endif
 
   /* **** Run-time data ****  */