Improve drawing with segments

src/pipelines/diffusion/diffuse.wgsl

@@ -1,8 +1,14 @@
 struct Settings {
   size : vec2<f32>,
+  swipePrevious : vec2<f32>,
+  swipeCurrent : vec2<f32>,
   diffusionRate : f32,
   decayRate : f32,
   deltaTime : f32,
+  time : f32,
+  swipeRadius : f32,
+  swipeBlur : f32,
+  isSwipeActive : f32
 };
 
 @group(0) @binding(0) var<uniform> settings : Settings;
@@ -11,18 +17,30 @@ struct Settings {
 
 @fragment
 fn fragment(@location(0) uv: vec2<f32>) -> @location(0) vec4<f32> {
-  let current = textureSample(trailMap, Sampler, uv).rgb;
-
-  let neighbours: vec3<f32> = (
-      textureSample(trailMap, Sampler, uv + vec2<f32>(0, 1) / settings.size).rgb
-    + textureSample(trailMap, Sampler, uv + vec2<f32>(0, -1) / settings.size).rgb
-    + textureSample(trailMap, Sampler, uv + vec2<f32>(-1, 0) / settings.size).rgb
-    + textureSample(trailMap, Sampler, uv + vec2<f32>(1, 0) / settings.size).rgb
+  var current = textureSample(trailMap, Sampler, uv);
+  
+  let neighbours: vec4<f32> = (
+      textureSample(trailMap, Sampler, uv + vec2<f32>(0, 1) / settings.size)
+    + textureSample(trailMap, Sampler, uv + vec2<f32>(0, -1) / settings.size)
+    + textureSample(trailMap, Sampler, uv + vec2<f32>(-1, 0) / settings.size)
+    + textureSample(trailMap, Sampler, uv + vec2<f32>(1, 0) / settings.size)
   );
 
-  return vec4(mix(
+  if (settings.isSwipeActive == 1.0) {
+    let pa = (uv - settings.swipePrevious) * normalize(settings.size);
+    let direction = (settings.swipeCurrent - settings.swipePrevious) * normalize(settings.size);
+    let q = clamp(dot(pa, direction) / dot(direction, direction), 0, 1);
+    let distance = length(pa - direction * q) - settings.swipeRadius;
+  
+    if(distance < 0) {
+      let opacity = -distance / settings.swipeBlur;
+      return clamp(vec4(1), current, vec4(1));
+    }
+  }
+
+  return mix(
     current,
     neighbours / 4.0,
     settings.diffusionRate
-  ) * (1.0 - settings.decayRate), 1.0);
+  ) * (1.0 - settings.decayRate);
 }