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, 59 insertions, 0 deletions

diff --git a/intern/cycles/blender/addon/ui.py b/intern/cycles/blender/addon/ui.py
index ee284dd899a..7036e58f6fb 100644
--- a/intern/cycles/blender/addon/ui.py
+++ b/intern/cycles/blender/addon/ui.py
@@ -278,6 +278,63 @@ class CYCLES_RENDER_PT_sampling_render_denoise(CyclesButtonsPanel, Panel):
             col.prop(cscene, "denoising_prefilter", text="Prefilter")
 
 
+class CYCLES_RENDER_PT_sampling_path_guiding(CyclesButtonsPanel, Panel):
+    bl_label = "Path Guiding"
+    bl_parent_id = "CYCLES_RENDER_PT_sampling"
+    bl_options = {'DEFAULT_CLOSED'}
+
+    @classmethod
+    def poll(cls, context):
+        from . import engine
+        return use_cpu(context) and engine.with_path_guiding()
+
+    def draw_header(self, context):
+        scene = context.scene
+        cscene = scene.cycles
+
+        self.layout.prop(cscene, "use_guiding", text="")
+
+    def draw(self, context):
+        scene = context.scene
+        cscene = scene.cycles
+
+        layout = self.layout
+        layout.use_property_split = True
+        layout.use_property_decorate = False
+        layout.active = cscene.use_guiding
+
+        col = layout.column(align=True)
+        col.prop(cscene, "use_surface_guiding")
+        col.prop(cscene, "use_volume_guiding")
+        col.prop(cscene, "guiding_training_samples")
+
+
+class CYCLES_RENDER_PT_sampling_path_guiding_debug(CyclesDebugButtonsPanel, Panel):
+    bl_label = "Debug"
+    bl_parent_id = "CYCLES_RENDER_PT_sampling_path_guiding"
+    bl_options = {'DEFAULT_CLOSED'}
+
+    def draw(self, context):
+        scene = context.scene
+        cscene = scene.cycles
+
+        layout = self.layout
+        layout.use_property_split = True
+        layout.use_property_decorate = False
+        layout.active = cscene.use_guiding
+
+        layout.prop(cscene, "guiding_distribution_type", text="Distribution Type")
+
+        col = layout.column(align=True)
+        col.prop(cscene, "surface_guiding_probability")
+        col.prop(cscene, "volume_guiding_probability")
+
+        col = layout.column(align=True)
+        col.prop(cscene, "use_deterministic_guiding")
+        col.prop(cscene, "use_guiding_direct_light")
+        col.prop(cscene, "use_guiding_mis_weights")
+
+
 class CYCLES_RENDER_PT_sampling_advanced(CyclesButtonsPanel, Panel):
     bl_label = "Advanced"
     bl_parent_id = "CYCLES_RENDER_PT_sampling"
@@ -2286,6 +2343,8 @@ classes = (
     CYCLES_RENDER_PT_sampling_viewport_denoise,
     CYCLES_RENDER_PT_sampling_render,
     CYCLES_RENDER_PT_sampling_render_denoise,
+    CYCLES_RENDER_PT_sampling_path_guiding,
+    CYCLES_RENDER_PT_sampling_path_guiding_debug,
     CYCLES_RENDER_PT_sampling_advanced,
     CYCLES_RENDER_PT_light_paths,
     CYCLES_RENDER_PT_light_paths_max_bounces,