Solari initial GI (#20020)

# Objective
- Add 1-bounce RT GI

## Solution

- Implement a very very basic version of ReSTIR GI
https://d1qx31qr3h6wln.cloudfront.net/publications/ReSTIR%20GI.pdf
- Pretty much a copy of the ReSTIR DI code, but adjusted for GI. 
- Didn't implement add more spatial samples, or do anything needed for
better quality.
- Didn't try to improve perf at all yet (it's actually faster than DI
though, unfortunately 😅)
- Didn't spend any time cleaning up the shared abstractions between
DI/GI

---

## Showcase
<img width="2564" height="1500" alt="image"
src="https://github.com/user-attachments/assets/1ff7be1c-7d7d-4e53-8aa6-bcec1553db3f"
/>

Author: JMS55

crates/bevy_solari/src/lib.rs

@@ -26,11 +26,13 @@ use bevy_render::settings::WgpuFeatures;
 /// An experimental set of plugins for raytraced lighting.
 ///
 /// This plugin group provides:
-/// * [`SolariLightingPlugin`] - Raytraced direct and indirect lighting (indirect lighting not yet implemented).
+/// * [`SolariLightingPlugin`] - Raytraced direct and indirect lighting.
 /// * [`RaytracingScenePlugin`] - BLAS building, resource and lighting binding.
+///
+/// There's also:
 /// * [`pathtracer::PathtracingPlugin`] - A non-realtime pathtracer for validation purposes (not added by default).
 ///
-/// To get started, add `RaytracingMesh3d` and `MeshMaterial3d::<StandardMaterial>` to your entities.
+/// To get started, add this plugin to your app, and then add `RaytracingMesh3d` and `MeshMaterial3d::<StandardMaterial>` to your entities.
 pub struct SolariPlugins;
 
 impl PluginGroup for SolariPlugins {

crates/bevy_solari/src/pathtracer/pathtracer.wgsl

@@ -47,7 +47,8 @@ fn pathtrace(@builtin(global_invocation_id) global_id: vec3<u32>) {
             if ray_t_min == 0.0 { radiance = ray_hit.material.emissive; }
 
             // Sample direct lighting
-            radiance += throughput * diffuse_brdf * sample_random_light(ray_hit.world_position, ray_hit.world_normal, &rng);
+            let direct_lighting = sample_random_light(ray_hit.world_position, ray_hit.world_normal, &rng);
+            radiance += throughput * diffuse_brdf * direct_lighting.radiance * direct_lighting.inverse_pdf;
 
             // Sample new ray direction from the material BRDF for next bounce
             ray_direction = sample_cosine_hemisphere(ray_hit.world_normal, &rng);

crates/bevy_solari/src/realtime/mod.rs

@@ -23,11 +23,16 @@ use node::SolariLightingNode;
 use prepare::prepare_solari_lighting_resources;
 use tracing::warn;
 
+/// Raytraced direct and indirect lighting.
+///
+/// When using this plugin, it's highly recommended to set `shadows_enabled: false` on all lights, as Solari replaces
+/// traditional shadow mapping.
 pub struct SolariLightingPlugin;
 
 impl Plugin for SolariLightingPlugin {
     fn build(&self, app: &mut App) {
         embedded_asset!(app, "restir_di.wgsl");
+        embedded_asset!(app, "restir_gi.wgsl");
 
         app.register_type::<SolariLighting>()
             .insert_resource(DefaultOpaqueRendererMethod::deferred());

crates/bevy_solari/src/realtime/node.rs

@@ -36,8 +36,10 @@ pub mod graph {
 
 pub struct SolariLightingNode {
     bind_group_layout: BindGroupLayout,
-    initial_and_temporal_pipeline: CachedComputePipelineId,
-    spatial_and_shade_pipeline: CachedComputePipelineId,
+    di_initial_and_temporal_pipeline: CachedComputePipelineId,
+    di_spatial_and_shade_pipeline: CachedComputePipelineId,
+    gi_initial_and_temporal_pipeline: CachedComputePipelineId,
+    gi_spatial_and_shade_pipeline: CachedComputePipelineId,
 }
 
 impl ViewNode for SolariLightingNode {
@@ -72,8 +74,10 @@ impl ViewNode for SolariLightingNode {
         let previous_view_uniforms = world.resource::<PreviousViewUniforms>();
         let frame_count = world.resource::<FrameCount>();
         let (
-            Some(initial_and_temporal_pipeline),
-            Some(spatial_and_shade_pipeline),
+            Some(di_initial_and_temporal_pipeline),
+            Some(di_spatial_and_shade_pipeline),
+            Some(gi_initial_and_temporal_pipeline),
+            Some(gi_spatial_and_shade_pipeline),
             Some(scene_bindings),
             Some(viewport),
             Some(gbuffer),
@@ -82,8 +86,10 @@ impl ViewNode for SolariLightingNode {
             Some(view_uniforms),
             Some(previous_view_uniforms),
         ) = (
-            pipeline_cache.get_compute_pipeline(self.initial_and_temporal_pipeline),
-            pipeline_cache.get_compute_pipeline(self.spatial_and_shade_pipeline),
+            pipeline_cache.get_compute_pipeline(self.di_initial_and_temporal_pipeline),
+            pipeline_cache.get_compute_pipeline(self.di_spatial_and_shade_pipeline),
+            pipeline_cache.get_compute_pipeline(self.gi_initial_and_temporal_pipeline),
+            pipeline_cache.get_compute_pipeline(self.gi_spatial_and_shade_pipeline),
             &scene_bindings.bind_group,
             camera.physical_viewport_size,
             view_prepass_textures.deferred_view(),
@@ -101,8 +107,18 @@ impl ViewNode for SolariLightingNode {
             &self.bind_group_layout,
             &BindGroupEntries::sequential((
                 view_target.get_unsampled_color_attachment().view,
-                solari_lighting_resources.reservoirs_a.as_entire_binding(),
-                solari_lighting_resources.reservoirs_b.as_entire_binding(),
+                solari_lighting_resources
+                    .di_reservoirs_a
+                    .as_entire_binding(),
+                solari_lighting_resources
+                    .di_reservoirs_b
+                    .as_entire_binding(),
+                solari_lighting_resources
+                    .gi_reservoirs_a
+                    .as_entire_binding(),
+                solari_lighting_resources
+                    .gi_reservoirs_b
+                    .as_entire_binding(),
                 gbuffer,
                 depth_buffer,
                 motion_vectors,
@@ -135,14 +151,20 @@ impl ViewNode for SolariLightingNode {
             ],
         );
 
-        pass.set_pipeline(initial_and_temporal_pipeline);
+        pass.set_pipeline(di_initial_and_temporal_pipeline);
         pass.set_push_constants(
             0,
             bytemuck::cast_slice(&[frame_index, solari_lighting.reset as u32]),
         );
         pass.dispatch_workgroups(viewport.x.div_ceil(8), viewport.y.div_ceil(8), 1);
 
-        pass.set_pipeline(spatial_and_shade_pipeline);
+        pass.set_pipeline(di_spatial_and_shade_pipeline);
+        pass.dispatch_workgroups(viewport.x.div_ceil(8), viewport.y.div_ceil(8), 1);
+
+        pass.set_pipeline(gi_initial_and_temporal_pipeline);
+        pass.dispatch_workgroups(viewport.x.div_ceil(8), viewport.y.div_ceil(8), 1);
+
+        pass.set_pipeline(gi_spatial_and_shade_pipeline);
         pass.dispatch_workgroups(viewport.x.div_ceil(8), viewport.y.div_ceil(8), 1);
 
         pass_span.end(&mut pass);
@@ -189,10 +211,12 @@ impl FromWorld for SolariLightingNode {
                 (
                     texture_storage_2d(
                         ViewTarget::TEXTURE_FORMAT_HDR,
-                        StorageTextureAccess::WriteOnly,
+                        StorageTextureAccess::ReadWrite,
                     ),
                     storage_buffer_sized(false, None),
                     storage_buffer_sized(false, None),
+                    storage_buffer_sized(false, None),
+                    storage_buffer_sized(false, None),
                     texture_2d(TextureSampleType::Uint),
                     texture_depth_2d(),
                     texture_2d(TextureSampleType::Float { filterable: true }),
@@ -204,9 +228,9 @@ impl FromWorld for SolariLightingNode {
             ),
         );
 
-        let initial_and_temporal_pipeline =
+        let di_initial_and_temporal_pipeline =
             pipeline_cache.queue_compute_pipeline(ComputePipelineDescriptor {
-                label: Some("solari_lighting_initial_and_temporal_pipeline".into()),
+                label: Some("solari_lighting_di_initial_and_temporal_pipeline".into()),
                 layout: vec![
                     scene_bindings.bind_group_layout.clone(),
                     bind_group_layout.clone(),
@@ -220,9 +244,9 @@ impl FromWorld for SolariLightingNode {
                 ..default()
             });
 
-        let spatial_and_shade_pipeline =
+        let di_spatial_and_shade_pipeline =
             pipeline_cache.queue_compute_pipeline(ComputePipelineDescriptor {
-                label: Some("solari_lighting_spatial_and_shade_pipeline".into()),
+                label: Some("solari_lighting_di_spatial_and_shade_pipeline".into()),
                 layout: vec![
                     scene_bindings.bind_group_layout.clone(),
                     bind_group_layout.clone(),
@@ -236,10 +260,46 @@ impl FromWorld for SolariLightingNode {
                 ..default()
             });
 
+        let gi_initial_and_temporal_pipeline =
+            pipeline_cache.queue_compute_pipeline(ComputePipelineDescriptor {
+                label: Some("solari_lighting_gi_initial_and_temporal_pipeline".into()),
+                layout: vec![
+                    scene_bindings.bind_group_layout.clone(),
+                    bind_group_layout.clone(),
+                ],
+                push_constant_ranges: vec![PushConstantRange {
+                    stages: ShaderStages::COMPUTE,
+                    range: 0..8,
+                }],
+                shader: load_embedded_asset!(world, "restir_gi.wgsl"),
+                shader_defs: vec![],
+                entry_point: Some("initial_and_temporal".into()),
+                zero_initialize_workgroup_memory: false,
+            });
+
+        let gi_spatial_and_shade_pipeline =
+            pipeline_cache.queue_compute_pipeline(ComputePipelineDescriptor {
+                label: Some("solari_lighting_gi_spatial_and_shade_pipeline".into()),
+                layout: vec![
+                    scene_bindings.bind_group_layout.clone(),
+                    bind_group_layout.clone(),
+                ],
+                push_constant_ranges: vec![PushConstantRange {
+                    stages: ShaderStages::COMPUTE,
+                    range: 0..8,
+                }],
+                shader: load_embedded_asset!(world, "restir_gi.wgsl"),
+                shader_defs: vec![],
+                entry_point: Some("spatial_and_shade".into()),
+                zero_initialize_workgroup_memory: false,
+            });
+
         Self {
             bind_group_layout,
-            initial_and_temporal_pipeline,
-            spatial_and_shade_pipeline,
+            di_initial_and_temporal_pipeline,
+            di_spatial_and_shade_pipeline,
+            gi_initial_and_temporal_pipeline,
+            gi_spatial_and_shade_pipeline,
         }
     }
 }

crates/bevy_solari/src/realtime/prepare.rs

@@ -17,14 +17,19 @@ use bevy_render::{
     renderer::RenderDevice,
 };
 
-/// Size of a Reservoir shader struct in bytes.
-const RESERVOIR_STRUCT_SIZE: u64 = 32;
+/// Size of a DI Reservoir shader struct in bytes.
+const DI_RESERVOIR_STRUCT_SIZE: u64 = 32;
+
+/// Size of a GI Reservoir shader struct in bytes.
+const GI_RESERVOIR_STRUCT_SIZE: u64 = 48;
 
 /// Internal rendering resources used for Solari lighting.
 #[derive(Component)]
 pub struct SolariLightingResources {
-    pub reservoirs_a: Buffer,
-    pub reservoirs_b: Buffer,
+    pub di_reservoirs_a: Buffer,
+    pub di_reservoirs_b: Buffer,
+    pub gi_reservoirs_a: Buffer,
+    pub gi_reservoirs_b: Buffer,
     pub previous_gbuffer: (Texture, TextureView),
     pub previous_depth: (Texture, TextureView),
     pub view_size: UVec2,
@@ -47,18 +52,30 @@ pub fn prepare_solari_lighting_resources(
             continue;
         }
 
-        let size = (view_size.x * view_size.y) as u64 * RESERVOIR_STRUCT_SIZE;
+        let di_reservoirs_a = render_device.create_buffer(&BufferDescriptor {
+            label: Some("solari_lighting_di_reservoirs_a"),
+            size: (view_size.x * view_size.y) as u64 * DI_RESERVOIR_STRUCT_SIZE,
+            usage: BufferUsages::STORAGE,
+            mapped_at_creation: false,
+        });
+
+        let di_reservoirs_b = render_device.create_buffer(&BufferDescriptor {
+            label: Some("solari_lighting_di_reservoirs_b"),
+            size: (view_size.x * view_size.y) as u64 * DI_RESERVOIR_STRUCT_SIZE,
+            usage: BufferUsages::STORAGE,
+            mapped_at_creation: false,
+        });
 
-        let reservoirs_a = render_device.create_buffer(&BufferDescriptor {
-            label: Some("solari_lighting_reservoirs_a"),
-            size,
+        let gi_reservoirs_a = render_device.create_buffer(&BufferDescriptor {
+            label: Some("solari_lighting_gi_reservoirs_a"),
+            size: (view_size.x * view_size.y) as u64 * GI_RESERVOIR_STRUCT_SIZE,
             usage: BufferUsages::STORAGE,
             mapped_at_creation: false,
         });
 
-        let reservoirs_b = render_device.create_buffer(&BufferDescriptor {
-            label: Some("solari_lighting_reservoirs_b"),
-            size,
+        let gi_reservoirs_b = render_device.create_buffer(&BufferDescriptor {
+            label: Some("solari_lighting_gi_reservoirs_b"),
+            size: (view_size.x * view_size.y) as u64 * GI_RESERVOIR_STRUCT_SIZE,
             usage: BufferUsages::STORAGE,
             mapped_at_creation: false,
         });
@@ -88,8 +105,10 @@ pub fn prepare_solari_lighting_resources(
         let previous_depth_view = previous_depth.create_view(&TextureViewDescriptor::default());
 
         commands.entity(entity).insert(SolariLightingResources {
-            reservoirs_a,
-            reservoirs_b,
+            di_reservoirs_a,
+            di_reservoirs_b,
+            gi_reservoirs_a,
+            gi_reservoirs_b,
             previous_gbuffer: (previous_gbuffer, previous_gbuffer_view),
             previous_depth: (previous_depth, previous_depth_view),
             view_size,