Clean up

src/pipelines/diffusion/diffuse.wgsl

@@ -3,9 +3,9 @@ struct Settings {
   decayRateTrails: f32,
   inverseDiffusionRateBrush: f32,
   decayRateBrush: f32,
-  diffusionNeighborDivisor: f32,
-  brushDecayAlphaOffset: f32,
-  padding0: f32,
+  diffusionNeighborScale: f32,
+  brushDecayAlphaMultiplier: f32,
+  brushDecayAlphaSubtract: f32,
   padding1: f32,
 };
 
@@ -60,8 +60,26 @@ fn main(
   let centerTileIndex = centerTilePosition.y * TILE_SIZE_X + centerTilePosition.x;
   var current = tile[centerTileIndex];
   let random = random_from_pixel(pixel);
-  let trailWeight = diffusion_weight(random, settings.inverseDiffusionRateTrails);
-  let brushWeight = diffusion_weight(random, settings.inverseDiffusionRateBrush);
+  let r2 = random * random;
+  let r4 = r2 * r2;
+  let r8 = r4 * r4;
+  let r16 = r8 * r8;
+  let trailWeight = diffusion_weight(
+    random,
+    r2,
+    r4,
+    r8,
+    r16,
+    settings.inverseDiffusionRateTrails
+  );
+  let brushWeight = diffusion_weight(
+    random,
+    r2,
+    r4,
+    r8,
+    r16,
+    settings.inverseDiffusionRateBrush
+  );
 
   current += (
       propagate(centerTileIndex, -1, -1, current, trailWeight, brushWeight)
@@ -73,11 +91,11 @@ fn main(
     + propagate(centerTileIndex, 0, -1, current, trailWeight, brushWeight)
     + propagate(centerTileIndex, 1, 0, current, trailWeight, brushWeight)
     + propagate(centerTileIndex, 0, 1, current, trailWeight, brushWeight)
-  ) / max(1.0, settings.diffusionNeighborDivisor);
+  ) * settings.diffusionNeighborScale;
 
   let decayed = clamp(vec4(
     current.rgb * settings.decayRateTrails,
-    max(0, current.a + (current.a - settings.brushDecayAlphaOffset) * settings.decayRateBrush)
+    max(0, current.a * settings.brushDecayAlphaMultiplier - settings.brushDecayAlphaSubtract)
   ), vec4(0), vec4(1));
 
   textureStore(trailMapOut, pixel, decayed);
@@ -110,9 +128,14 @@ fn random_from_pixel(pixel: vec2<i32>) -> f32 {
   return f32(hash) * 2.3283064365386963e-10;
 }
 
-fn diffusion_weight(random: f32, inverseRate: f32) -> f32 {
-  let r = clamp(random, 0.0, 1.0);
-
+fn diffusion_weight(
+  r: f32,
+  r2: f32,
+  r4: f32,
+  r8: f32,
+  r16: f32,
+  inverseRate: f32
+) -> f32 {
   if inverseRate < 1.0 {
     let rootApproximation = r / max(0.5 + r * 0.5, 0.0001);
     return mix(
@@ -122,22 +145,18 @@ fn diffusion_weight(random: f32, inverseRate: f32) -> f32 {
     );
   }
 
-  let r2 = r * r;
   if inverseRate < 2.0 {
     return mix(r, r2, inverseRate - 1.0);
   }
 
-  let r4 = r2 * r2;
   if inverseRate < 4.0 {
     return mix(r2, r4, (inverseRate - 2.0) * 0.5);
   }
 
-  let r8 = r4 * r4;
   if inverseRate < 8.0 {
     return mix(r4, r8, (inverseRate - 4.0) * 0.25);
   }
 
-  let r16 = r8 * r8;
   return mix(r8, r16, clamp((inverseRate - 8.0) * 0.125, 0.0, 1.0))
     * min(1.0, 16.0 / inverseRate);
 }