Remove alpha from deposit layer

src/config/default-settings.ts

@@ -35,10 +35,8 @@ export const defaultSettings: GardenDefaultSettings = {
   randomTimeScale: 0.34816,
 
   diffusionRateTrails: 0.22,
-  decayRateBrush: 18,
   diffusionDecayRateDivisor: 1000,
   diffusionNeighborDivisor: 8,
-  brushDecayAlphaOffset: 1.001,
   brushEffectDuration: 8,
 
   brushCurveResolution: 12,
@@ -48,7 +46,6 @@ export const defaultSettings: GardenDefaultSettings = {
   brushCurveSegmentBrushRadiusRatio: 0.65,
   brushSmoothingMinSampleDistance: 0.5,
 
-  brushAlpha: 1,
   brushDiscardThreshold: 0.02,
   brushGrainNoiseScale: 22,
   brushGrainNoiseOffsetX: 0.31,
@@ -56,12 +53,12 @@ export const defaultSettings: GardenDefaultSettings = {
   brushGrainMinStrength: 0.45,
   brushGrainMaxStrength: 1,
 
-  eraserClearAlpha: 0,
   eraserClearBlue: 0,
   eraserClearGreen: 0,
   eraserClearRed: 0,
   eraserLineDistanceEpsilon: 0.0001,
   eraserMaskAlphaThreshold: 0.5,
+  eraserMaskErasedValue: 0,
 
   adaptiveCapInitial: 1_000_000,
   adaptiveCapMin: 50_000,

src/config/types.ts

@@ -28,12 +28,12 @@ export type GardenRuntimeSettings = {
   brushCurveSegmentBrushRadiusRatio: number;
   brushEffectDuration: number;
   brushSmoothingMinSampleDistance: number;
-  eraserClearAlpha: number;
   eraserClearBlue: number;
   eraserClearGreen: number;
   eraserClearRed: number;
   eraserLineDistanceEpsilon: number;
   eraserMaskAlphaThreshold: number;
+  eraserMaskErasedValue: number;
   eraserSize: number;
   internalRenderAreaMegapixels: number;
   mirrorSegmentCount: number;

src/game-loop/game-loop-resources.ts

@@ -163,7 +163,7 @@ export class GameLoopResources {
       eraserClearRed: runtimeSettings.eraserClearRed,
       eraserClearGreen: runtimeSettings.eraserClearGreen,
       eraserClearBlue: runtimeSettings.eraserClearBlue,
-      eraserClearAlpha: runtimeSettings.eraserClearAlpha,
+      eraserMaskErasedValue: runtimeSettings.eraserMaskErasedValue,
     });
   }
 

src/pipelines/agents/agent.wgsl

@@ -215,7 +215,8 @@ fn agent_finalize(
   // Writes only this agent's last-writer-wins deposit into a per-frame-cleared
   // depositMap. Storage textures do not blend concurrent compute writes, so
   // overlapping agents intentionally collapse to whichever write wins. The
-  // diffusion pass then sums trailMap + depositMap at tile-load time.
+  // diffusion pass then sums trailMap + depositMap at tile-load time. The
+  // rgba8unorm alpha lane is unused, so deposits leave it at zero.
   textureStore(
     trailMapOut,
     vec2<i32>(nextPosition),

src/pipelines/brush/brush-pipeline.ts

@@ -18,7 +18,6 @@ import shader from './brush.wgsl?raw';
 
 export interface BrushSettings {
   brushSize: number;
-  brushAlpha: number;
   brushDiscardThreshold: number;
   brushGrainNoiseScale: number;
   brushGrainNoiseOffsetX: number;
@@ -45,7 +44,6 @@ const setBrushUniformValues = (
   target: Float32Array,
   {
     brushSize,
-    brushAlpha,
     brushDiscardThreshold,
     brushGrainNoiseScale,
     brushGrainNoiseOffsetX,
@@ -65,17 +63,16 @@ const setBrushUniformValues = (
 
   target[0] = brushRadius;
   target[1] = brushRadius * brushRadius;
-  // target[2], target[3] are WGSL alignment padding for brushValue:vec4 — never read by the shader.
+  // target[2], target[3] are WGSL alignment padding for brushColor:vec3 — never read by the shader.
   target[4] = selectedColorIndex === 0 ? 1 : 0;
   target[5] = selectedColorIndex === 1 ? 1 : 0;
   target[6] = selectedColorIndex === 2 ? 1 : 0;
-  target[7] = brushAlpha;
-  target[8] = 1 / Math.max(Number.EPSILON, brushGrainNoiseScale * safePixelRatio);
-  target[9] = brushGrainNoiseOffsetX;
-  target[10] = brushGrainNoiseOffsetY;
-  target[11] = brushDiscardThreshold;
-  target[12] = brushGrainMinStrength;
-  target[13] = brushGrainMaxStrength;
+  target[7] = 1 / Math.max(Number.EPSILON, brushGrainNoiseScale * safePixelRatio);
+  target[8] = brushGrainNoiseOffsetX;
+  target[9] = brushGrainNoiseOffsetY;
+  target[10] = brushDiscardThreshold;
+  target[11] = brushGrainMinStrength;
+  target[12] = brushGrainMaxStrength;
 };
 
 export class BrushPipeline {

src/pipelines/brush/brush.wgsl

@@ -3,10 +3,10 @@ const SEGMENT_LENGTH_EPSILON: f32 = 0.0001;
 struct Settings {
   brushRadius: f32,
   brushRadiusSquared: f32,
-  // padding to 16-byte alignment for the following vec4
+  // padding to 16-byte alignment for the following vec3
   _pad0: f32,
   _pad1: f32,
-  brushValue: vec4<f32>,
+  brushColor: vec3<f32>,
   brushGrainNoiseScale: f32,
   brushGrainNoiseOffsetX: f32,
   brushGrainNoiseOffsetY: f32,
@@ -115,5 +115,7 @@ fn brushStrength(
 }
 
 fn brushOutput(strength: f32) -> vec4<f32> {
-  return vec4(settings.brushValue.rgb * strength, settings.brushValue.a * strength);
+  // The rgba8unorm source map needs a vec4; its alpha lane is unused, so the
+  // brush leaves it at zero.
+  return vec4(settings.brushColor * strength, 0.0);
 }

src/pipelines/diffusion/diffuse.wgsl

@@ -2,11 +2,7 @@ struct Settings {
   inverseDiffusionRateTrails: f32,
   decayRateTrails: f32,
   diffusionNeighborScale: f32,
-  brushDecayAlphaMultiplier: f32,
-  brushDecayAlphaSubtract: f32,
   padding0: f32,
-  padding1: f32,
-  padding2: f32,
 };
 
 const WORKGROUP_SIZE_X = __WORKGROUP_SIZE__u;
@@ -32,7 +28,9 @@ const HASH_TO_UNIT_FLOAT: f32 = 2.3283064365386963e-10;
 // in the same frame.
 @group(0) @binding(3) var depositMap: texture_2d<f32>;
 
-var<workgroup> tile: array<vec4<f32>, TILE_TEXEL_COUNT>;
+// Only the color channels take part in the simulation; the alpha lane of the
+// rgba8unorm trail and source maps is unused and always stored as zero.
+var<workgroup> tile: array<vec3<f32>, TILE_TEXEL_COUNT>;
 var<workgroup> tileTrailStrength: array<f32, TILE_TEXEL_COUNT>;
 
 @compute @workgroup_size(__WORKGROUP_SIZE__, __WORKGROUP_SIZE__)
@@ -53,10 +51,10 @@ fn main(
       vec2<i32>(0, 0),
       textureBound
     );
-    let texel = textureLoad(trailMap, sourcePixel, 0)
-      + textureLoad(depositMap, sourcePixel, 0);
+    let texel = textureLoad(trailMap, sourcePixel, 0).rgb
+      + textureLoad(depositMap, sourcePixel, 0).rgb;
     tile[tileIndex] = texel;
-    tileTrailStrength[tileIndex] = length(texel.rgb);
+    tileTrailStrength[tileIndex] = length(texel);
   }
 
   workgroupBarrier();
@@ -106,25 +104,23 @@ fn main(
     + propagate_value(nBR, sBR, current, trailWeight);
 
   let updated = current + propagated * settings.diffusionNeighborScale;
-  let decayed = clamp(vec4(
-    updated.rgb * settings.decayRateTrails - vec3(TRAIL_RGB_DECAY_SUBTRACT),
-    updated.a * settings.brushDecayAlphaMultiplier - settings.brushDecayAlphaSubtract
-  ), vec4(0), vec4(1));
+  let decayed = clamp(
+    updated * settings.decayRateTrails - vec3(TRAIL_RGB_DECAY_SUBTRACT),
+    vec3(0),
+    vec3(1)
+  );
 
-  textureStore(trailMapOut, pixel, decayed);
+  textureStore(trailMapOut, pixel, vec4(decayed, 0.0));
 }
 
 fn propagate_value(
-  neighbour: vec4<f32>,
+  neighbour: vec3<f32>,
   neighbourStrength: f32,
-  current: vec4<f32>,
+  current: vec3<f32>,
   trailWeight: f32
-) -> vec4<f32> {
-  let difference = clamp(neighbour - current, vec4(0), vec4(1));
-  return vec4(
-    vec3(neighbourStrength * trailWeight),
-    neighbour.a * trailWeight
-  ) * difference;
+) -> vec3<f32> {
+  let difference = clamp(neighbour - current, vec3(0), vec3(1));
+  return vec3(neighbourStrength * trailWeight) * difference;
 }
 
 fn random_from_pixel(pixel: vec2<i32>) -> f32 {

src/pipelines/diffusion/diffusion-pipeline.ts

@@ -12,22 +12,10 @@ import shader from './diffuse.wgsl?raw';
 export interface DiffusionSettings {
   diffusionRateTrails: number;
   decayRateTrails: number;
-  decayRateBrush: number;
   diffusionDecayRateDivisor: number;
   diffusionNeighborDivisor: number;
-  brushDecayAlphaOffset: number;
 }
 
-type DiffusionUniformSettings = Pick<
-  DiffusionSettings,
-  | 'diffusionRateTrails'
-  | 'decayRateTrails'
-  | 'decayRateBrush'
-  | 'diffusionDecayRateDivisor'
-  | 'diffusionNeighborDivisor'
-  | 'brushDecayAlphaOffset'
->;
-
 const MIN_DIFFUSION_RATE = 0.000001;
 
 const getSafeInverseDiffusionRate = (diffusionRate: number): number =>
@@ -41,30 +29,23 @@ const setDiffusionUniformValues = (
   {
     diffusionRateTrails,
     decayRateTrails,
-    decayRateBrush,
     diffusionDecayRateDivisor,
     diffusionNeighborDivisor,
-    brushDecayAlphaOffset,
-  }: DiffusionUniformSettings
+  }: DiffusionSettings
 ): void => {
   const decayDivisor = Math.max(Number.EPSILON, diffusionDecayRateDivisor);
-  const brushDecayRate = decayRateBrush / decayDivisor;
   const neighborDivisor = Number.isFinite(diffusionNeighborDivisor)
     ? Math.max(1, diffusionNeighborDivisor)
     : 1;
   target[0] = getSafeInverseDiffusionRate(diffusionRateTrails);
   target[1] = decayRateTrails / decayDivisor;
   target[2] = 1 / neighborDivisor;
-  target[3] = 1 + brushDecayRate;
-  target[4] = brushDecayAlphaOffset * brushDecayRate;
-  target[5] = 0;
-  target[6] = 0;
-  target[7] = 0;
+  // target[3] is WGSL 16-byte alignment padding — never read by the shader.
 };
 
 export class DiffusionPipeline {
   private static readonly WORKGROUP_SIZE = 16;
-  private static readonly UNIFORM_COUNT = 8;
+  private static readonly UNIFORM_COUNT = 4;
 
   private readonly bindGroupLayout: GPUBindGroupLayout;
   private readonly pipeline: GPUComputePipeline;
@@ -136,18 +117,14 @@ export class DiffusionPipeline {
   public setParameters({
     diffusionRateTrails,
     decayRateTrails,
-    decayRateBrush,
     diffusionDecayRateDivisor,
     diffusionNeighborDivisor,
-    brushDecayAlphaOffset,
   }: DiffusionSettings) {
     setDiffusionUniformValues(this.uniformValues, {
       diffusionRateTrails,
       decayRateTrails,
-      decayRateBrush,
       diffusionDecayRateDivisor,
       diffusionNeighborDivisor,
-      brushDecayAlphaOffset,
     });
     writeBufferIfChanged(
       this.device,

src/pipelines/eraser/eraser-texture-pipeline.ts

@@ -24,7 +24,7 @@ interface EraserTextureParameters {
   eraserClearRed: number;
   eraserClearGreen: number;
   eraserClearBlue: number;
-  eraserClearAlpha: number;
+  eraserMaskErasedValue: number;
 }
 
 const UNIFORM_COUNT = 8;
@@ -110,7 +110,7 @@ export class EraserTexturePipeline {
     eraserClearRed,
     eraserClearGreen,
     eraserClearBlue,
-    eraserClearAlpha,
+    eraserMaskErasedValue,
   }: EraserTextureParameters): void {
     const eraserRadius = eraserSize / 2;
 
@@ -119,7 +119,7 @@ export class EraserTexturePipeline {
     this.uniformValues[2] = eraserClearRed;
     this.uniformValues[3] = eraserClearGreen;
     this.uniformValues[4] = eraserClearBlue;
-    this.uniformValues[5] = eraserClearAlpha;
+    this.uniformValues[5] = eraserMaskErasedValue;
     this.uniformValues[6] = eraserRadius;
     writeBufferIfChanged(
       this.device,

src/pipelines/eraser/eraser-texture.wgsl

@@ -4,7 +4,7 @@ struct Settings {
   clearRed: f32,
   clearGreen: f32,
   clearBlue: f32,
-  clearAlpha: f32,
+  erasedMaskValue: f32,
   eraserRadius: f32,
 };
 
@@ -66,14 +66,16 @@ fn fragmentCombined(
 }
 
 fn getEraserMaskValue() -> vec4<f32> {
-  return vec4<f32>(settings.clearAlpha, 0.0, 0.0, 1.0);
+  return vec4<f32>(settings.erasedMaskValue, 0.0, 0.0, 1.0);
 }
 
 fn getEraserClearValue() -> vec4<f32> {
+  // The rgba8unorm trail and source maps need a vec4; their alpha lane is
+  // unused, so erased texels keep it at zero.
   return vec4<f32>(
     settings.clearRed,
     settings.clearGreen,
     settings.clearBlue,
-    settings.clearAlpha
+    0.0
   );
 }