,

src/pipelines/eraser/eraser-texture.wgsl

@@ -14,6 +14,12 @@ struct VertexOutput {
   @location(2) end: vec2<f32>
 }
 
+struct EraserTextureTargets {
+  @location(0) source: vec4<f32>,
+  @location(1) influence: vec4<f32>,
+  @location(2) trail: vec4<f32>,
+}
+
 @vertex
 fn vertex(
   @location(0) screenPosition: vec2<f32>,
@@ -31,13 +37,35 @@ fn fragment(
   @location(1) start: vec2<f32>,
   @location(2) end: vec2<f32>
 ) -> @location(0) vec4<f32> {
-  if distanceSquaredFromLine(screenPosition, start, end) > settings.eraserRadiusSquared {
+  if shouldDiscardEraserFragment(screenPosition, start, end) {
     discard;
   }
 
   return vec4<f32>(0.0, 0.0, 0.0, 0.0);
 }
 
+@fragment
+fn fragmentMrt(
+  @location(0) screenPosition: vec2<f32>,
+  @location(1) start: vec2<f32>,
+  @location(2) end: vec2<f32>
+) -> EraserTextureTargets {
+  if shouldDiscardEraserFragment(screenPosition, start, end) {
+    discard;
+  }
+
+  let cleared = vec4<f32>(0.0, 0.0, 0.0, 0.0);
+  return EraserTextureTargets(cleared, cleared, cleared);
+}
+
+fn shouldDiscardEraserFragment(
+  screenPosition: vec2<f32>,
+  start: vec2<f32>,
+  end: vec2<f32>
+) -> bool {
+  return distanceSquaredFromLine(screenPosition, start, end) > settings.eraserRadiusSquared;
+}
+
 fn distanceSquaredFromLine(position: vec2<f32>, start: vec2<f32>, end: vec2<f32>) -> f32 {
   let pa = position - start;
   let direction = end - start;