Solari: More reactive world cache (#21810)

Thanks to Guillaume Boissé, the world cache is both more stable in
static scenarios, and more reactive in dynamic scenarios!

https://bsky.app/profile/gboisse.bsky.social/post/3m5blga3ftk2a

Co-authored-by: Alice Cecile <[email protected]>

Author: JMS55

crates/bevy_solari/src/realtime/node.rs

@@ -185,6 +185,7 @@ impl ViewNode for SolariLightingNode {
                 s.world_cache_life.as_entire_binding(),
                 s.world_cache_radiance.as_entire_binding(),
                 s.world_cache_geometry_data.as_entire_binding(),
+                s.world_cache_luminance_deltas.as_entire_binding(),
                 s.world_cache_active_cells_new_radiance.as_entire_binding(),
                 s.world_cache_a.as_entire_binding(),
                 s.world_cache_b.as_entire_binding(),
@@ -399,6 +400,7 @@ impl FromWorld for SolariLightingNode {
                     storage_buffer_sized(false, None),
                     storage_buffer_sized(false, None),
                     storage_buffer_sized(false, None),
+                    storage_buffer_sized(false, None),
                 ),
             ),
         );

crates/bevy_solari/src/realtime/prepare.rs

@@ -56,6 +56,7 @@ pub struct SolariLightingResources {
     pub world_cache_life: Buffer,
     pub world_cache_radiance: Buffer,
     pub world_cache_geometry_data: Buffer,
+    pub world_cache_luminance_deltas: Buffer,
     pub world_cache_active_cells_new_radiance: Buffer,
     pub world_cache_a: Buffer,
     pub world_cache_b: Buffer,
@@ -202,6 +203,13 @@ pub fn prepare_solari_lighting_resources(
             mapped_at_creation: false,
         });
 
+        let world_cache_luminance_deltas = render_device.create_buffer(&BufferDescriptor {
+            label: Some("solari_lighting_world_cache_luminance_deltas"),
+            size: WORLD_CACHE_SIZE * size_of::<f32>() as u64,
+            usage: BufferUsages::STORAGE,
+            mapped_at_creation: false,
+        });
+
         let world_cache_active_cells_new_radiance =
             render_device.create_buffer(&BufferDescriptor {
                 label: Some("solari_lighting_world_cache_active_cells_new_radiance"),
@@ -257,6 +265,7 @@ pub fn prepare_solari_lighting_resources(
             world_cache_life,
             world_cache_radiance,
             world_cache_geometry_data,
+            world_cache_luminance_deltas,
             world_cache_active_cells_new_radiance,
             world_cache_a,
             world_cache_b,

crates/bevy_solari/src/realtime/world_cache_compact.wgsl

@@ -1,4 +1,14 @@
-#import bevy_solari::world_cache::{WORLD_CACHE_EMPTY_CELL, world_cache_life, world_cache_checksums, world_cache_radiance, world_cache_a, world_cache_b, world_cache_active_cell_indices, world_cache_active_cells_count}
+#import bevy_solari::world_cache::{
+    WORLD_CACHE_EMPTY_CELL,
+    world_cache_life,
+    world_cache_checksums,
+    world_cache_radiance,
+    world_cache_luminance_deltas,
+    world_cache_a,
+    world_cache_b,
+    world_cache_active_cell_indices,
+    world_cache_active_cells_count,
+}
 
 @group(2) @binding(0) var<storage, read_write> world_cache_active_cells_dispatch: vec3<u32>;
 
@@ -15,6 +25,7 @@ fn decay_world_cache(@builtin(global_invocation_id) global_id: vec3<u32>) {
         if life == 0u {
             world_cache_checksums[global_id.x] = WORLD_CACHE_EMPTY_CELL;
             world_cache_radiance[global_id.x] = vec4(0.0);
+            world_cache_luminance_deltas[global_id.x] = 0.0;
         }
     }
 }

crates/bevy_solari/src/realtime/world_cache_query.wgsl

@@ -4,7 +4,7 @@
 #import bevy_render::maths::orthonormalize
 
 /// How responsive the world cache is to changes in lighting (higher is less responsive, lower is more responsive)
-const WORLD_CACHE_MAX_TEMPORAL_SAMPLES: f32 = 10.0;
+const WORLD_CACHE_MAX_TEMPORAL_SAMPLES: f32 = 32.0;
 /// How many direct light samples each cell takes when updating each frame
 const WORLD_CACHE_DIRECT_LIGHT_SAMPLE_COUNT: u32 = 32u;
 /// Maximum amount of distance to trace GI rays between two cache cells
@@ -38,11 +38,12 @@ struct WorldCacheGeometryData {
 #endif
 @group(1) @binding(16) var<storage, read_write> world_cache_radiance: array<vec4<f32>, #{WORLD_CACHE_SIZE}>;
 @group(1) @binding(17) var<storage, read_write> world_cache_geometry_data: array<WorldCacheGeometryData, #{WORLD_CACHE_SIZE}>;
-@group(1) @binding(18) var<storage, read_write> world_cache_active_cells_new_radiance: array<vec3<f32>, #{WORLD_CACHE_SIZE}>;
-@group(1) @binding(19) var<storage, read_write> world_cache_a: array<u32, #{WORLD_CACHE_SIZE}>;
-@group(1) @binding(20) var<storage, read_write> world_cache_b: array<u32, 1024u>;
-@group(1) @binding(21) var<storage, read_write> world_cache_active_cell_indices: array<u32, #{WORLD_CACHE_SIZE}>;
-@group(1) @binding(22) var<storage, read_write> world_cache_active_cells_count: u32;
+@group(1) @binding(18) var<storage, read_write> world_cache_luminance_deltas: array<f32, #{WORLD_CACHE_SIZE}>;
+@group(1) @binding(19) var<storage, read_write> world_cache_active_cells_new_radiance: array<vec3<f32>, #{WORLD_CACHE_SIZE}>;
+@group(1) @binding(20) var<storage, read_write> world_cache_a: array<u32, #{WORLD_CACHE_SIZE}>;
+@group(1) @binding(21) var<storage, read_write> world_cache_b: array<u32, 1024u>;
+@group(1) @binding(22) var<storage, read_write> world_cache_active_cell_indices: array<u32, #{WORLD_CACHE_SIZE}>;
+@group(1) @binding(23) var<storage, read_write> world_cache_active_cells_count: u32;
 
 #ifndef WORLD_CACHE_NON_ATOMIC_LIFE_BUFFER
 fn query_world_cache(world_position: vec3<f32>, world_normal: vec3<f32>, view_position: vec3<f32>, cell_lifetime: u32, rng: ptr<function, u32>) -> vec3<f32> {

crates/bevy_solari/src/realtime/world_cache_update.wgsl

@@ -14,6 +14,7 @@
     world_cache_life,
     world_cache_geometry_data,
     world_cache_radiance,
+    world_cache_luminance_deltas,
     world_cache_active_cells_new_radiance,
 }
 
@@ -54,11 +55,19 @@ fn blend_new_samples(@builtin(global_invocation_id) active_cell_id: vec3<u32>) {
 
         let old_radiance = world_cache_radiance[cell_index];
         let new_radiance = world_cache_active_cells_new_radiance[active_cell_id.x];
+        let luminance_delta = world_cache_luminance_deltas[cell_index];
+
+        // https://bsky.app/profile/gboisse.bsky.social/post/3m5blga3ftk2a
         let sample_count = min(old_radiance.a + 1.0, WORLD_CACHE_MAX_TEMPORAL_SAMPLES);
+        let alpha = abs(luminance_delta) / max(luminance(old_radiance.rgb), 0.001);
+        let max_sample_count = mix(WORLD_CACHE_MAX_TEMPORAL_SAMPLES, 1.0, pow(saturate(alpha), 1.0 / 8.0));
+        let blend_amount = 1.0 / min(sample_count, max_sample_count);
 
-        let blended_radiance = mix(old_radiance.rgb, new_radiance, 1.0 / sample_count);
+        let blended_radiance = mix(old_radiance.rgb, new_radiance, blend_amount);
+        let blended_luminance_delta = mix(luminance_delta, luminance(blended_radiance) - luminance(old_radiance.rgb), 1.0 / 8.0);
 
         world_cache_radiance[cell_index] = vec4(blended_radiance, sample_count);
+        world_cache_luminance_deltas[cell_index] = blended_luminance_delta;
     }
 }