Solari: Skip ReSTIR GI for smooth metallic surfaces (#22671)

# Objective

- Save perf on scenes with smooth metallic surfaces

## Solution

- Skip ReSTIR GI for these surfaces as the contribution will be zero
anyways

## Testing

- Tested on a half metallic half non-metallic scene with varying
roughness

Author: JMS55

crates/bevy_solari/src/realtime/restir_gi.wgsl

@@ -12,6 +12,7 @@ enable wgpu_ray_query;
 #import bevy_solari::scene_bindings::{trace_ray, resolve_ray_hit_full, RAY_T_MIN, RAY_T_MAX}
 #import bevy_solari::world_cache::{query_world_cache, WORLD_CACHE_CELL_LIFETIME}
 #import bevy_solari::realtime_bindings::{view_output, gi_reservoirs_a, gi_reservoirs_b, gbuffer, depth_buffer, motion_vectors, previous_gbuffer, previous_depth_buffer, view, previous_view, constants, Reservoir}
+#import bevy_solari::specular_gi::DIFFUSE_GI_REUSE_ROUGHNESS_THRESHOLD
 
 const SPATIAL_REUSE_RADIUS_PIXELS = 30.0;
 const CONFIDENCE_WEIGHT_CAP = 8.0;
@@ -29,6 +30,10 @@ fn initial_and_temporal(@builtin(global_invocation_id) global_id: vec3<u32>) {
         return;
     }
     let surface = gpixel_resolve(textureLoad(gbuffer, global_id.xy, 0), depth, global_id.xy, view.main_pass_viewport.zw, view.world_from_clip);
+    if surface.material.metallic > 0.9999 && surface.material.roughness <= DIFFUSE_GI_REUSE_ROUGHNESS_THRESHOLD {
+        gi_reservoirs_b[pixel_index] = empty_reservoir();
+        return;
+    }
 
     let initial_reservoir = generate_initial_reservoir(surface.world_position, surface.world_normal, &rng);
     let temporal = load_temporal_reservoir(global_id.xy, depth, surface.world_position, surface.world_normal);
@@ -51,6 +56,10 @@ fn spatial_and_shade(@builtin(global_invocation_id) global_id: vec3<u32>) {
         return;
     }
     let surface = gpixel_resolve(textureLoad(gbuffer, global_id.xy, 0), depth, global_id.xy, view.main_pass_viewport.zw, view.world_from_clip);
+    if surface.material.metallic > 0.9999 && surface.material.roughness <= DIFFUSE_GI_REUSE_ROUGHNESS_THRESHOLD {
+        gi_reservoirs_a[pixel_index] = empty_reservoir();
+        return;
+    }
 
     let input_reservoir = gi_reservoirs_b[pixel_index];
     let spatial = load_spatial_reservoir(global_id.xy, depth, surface.world_position, surface.world_normal, &rng);