Refactor and improve brush

src/pipelines/brush/brush.wgsl

@@ -1,25 +1,49 @@
+struct Settings {
+  size : vec2<f32>,
+  deltaTime : f32,
+  time : f32,
+  brushWidth: f32,
+  brushBlurWidth: f32
+};
+
+@group(0) @binding(0) var<uniform> settings : Settings;
+@group(0) @binding(1) var Sampler: sampler;
+@group(0) @binding(2) var noise : texture_2d<f32>;
+
 struct VertexOutput {
   @builtin(position) position : vec4<f32>,
-  @location(0) uv : vec2<f32>
+  @location(0) screenPosition : vec2<f32>,
+  @location(1) start : vec2<f32>,
+  @location(2) end : vec2<f32>
 }
 
 @vertex
 fn vertex(
-  @location(0) uv : vec2<f32>
+  @location(0) screenPosition : vec2<f32>,
+  @location(1) @interpolate(flat) start : vec2<f32>,
+  @location(2) @interpolate(flat) end : vec2<f32>
 ) -> VertexOutput {
+  let uv = screenPosition / settings.size;
   let position = uv * 2.0 - 1.0;
-  return VertexOutput(vec4(position, 0.0, 1.0), uv);
+  return VertexOutput(vec4(position, 0.0, 1.0), screenPosition, start, end);
 }
 
-struct Settings {
-  size : vec2<f32>,
-  deltaTime : f32,
-  time : f32
-};
-
-@group(0) @binding(0) var<uniform> settings : Settings;
-
 @fragment
-fn fragment(@location(0) uv: vec2<f32>) -> @location(0) vec4<f32> {
-  return vec4(1, settings.size.x  * 0, 0, 1);
+fn fragment(
+  @location(0) screenPosition: vec2<f32>,
+  @location(1) start: vec2<f32>,
+  @location(2) end: vec2<f32>
+) -> @location(0) vec4<f32> {
+    let pa = (screenPosition - start);
+    let direction = (end - start);
+    let q = clamp(dot(pa, direction) / dot(direction, direction), 0, 1);
+    let noise = textureSample(noise, Sampler, screenPosition / settings.size);
+
+    let distance = length(pa - direction * q) + noise.r * 5;
+
+    if(distance > settings.brushWidth) {
+      discard;
+    }
+
+    return vec4(clamp((settings.brushWidth - distance) / settings.brushBlurWidth, 0, 1));
 }