Copy from https://playground.babylonjs.com/#GXJ3FZ#51

src/pipelines/diffusion/diffuse.wgsl

@@ -0,0 +1,34 @@
+struct VertexOutput {
+  @builtin(position) Position : vec4<f32>,
+  @location(0) fragUV : vec2<f32>,
+}
+
+@vertex
+fn vertex(@builtin(vertex_index) i : u32) -> VertexOutput {
+  var pos = array<vec2<f32>, 4>(
+    vec2(-1.0, 1.0),
+    vec2(-1.0, -1.0),
+    vec2(1.0, 1.0),
+    vec2(1.0, -1.0),
+  );
+
+  var output : VertexOutput;
+  output.Position = vec4<f32>(pos[i], 0.0, 1.0);
+  output.fragUV = output.Position.xy * 0.5 + 0.5;
+  return output;
+}
+
+
+@group(0) @binding(0) var mySampler: sampler;
+@group(0) @binding(1) var TargetTexture : texture_2d<f32>;
+
+
+@fragment
+fn fragment(@location(0) fragUV: vec2<f32>) -> @location(0) vec4<f32> {
+  // return vec4(1.0, 0.0, 0.0, 1.0);
+  return mix(
+    vec4(textureSample(TargetTexture, mySampler, fragUV).rgb, 0.1),
+    vec4(1.0, 1.0, 1.0, 1.0), 
+    0.01
+  );
+}

src/pipelines/diffusion/diffusion-pipeline.ts

@@ -0,0 +1,81 @@
+import shader from './diffuse.wgsl';
+
+export class DiffusionPipeline {
+  private readonly pipeline: GPURenderPipeline;
+  private bindGroup?: GPUBindGroup;
+  private previousTrailMapIn?: GPUTexture;
+
+  public constructor(private readonly device: GPUDevice) {
+    this.pipeline = device.createRenderPipeline({
+      layout: 'auto',
+      vertex: {
+        module: device.createShaderModule({
+          code: shader,
+        }),
+        entryPoint: 'vertex',
+      },
+      fragment: {
+        module: device.createShaderModule({
+          code: shader,
+        }),
+        entryPoint: 'fragment',
+        targets: [
+          {
+            format: 'rgba16float',
+          },
+        ],
+      },
+      primitive: {
+        topology: 'triangle-strip',
+      },
+    });
+  }
+
+  public execute(
+    commandEncoder: GPUCommandEncoder,
+    trailMapIn: GPUTexture,
+    trailMapOut: GPUTexture
+  ) {
+    this.ensureBindGroupExists(trailMapIn);
+
+    const renderPassDescriptor: GPURenderPassDescriptor = {
+      colorAttachments: [
+        {
+          view: trailMapOut.createView(),
+          clearValue: { r: 1.0, g: 1.0, b: 1.0, a: 1.0 },
+          loadOp: 'clear',
+          storeOp: 'store',
+        },
+      ],
+    };
+
+    const renderPassEncoder = commandEncoder.beginRenderPass(renderPassDescriptor);
+    renderPassEncoder.setBindGroup(0, this.bindGroup!);
+    renderPassEncoder.setPipeline(this.pipeline);
+    renderPassEncoder.draw(4, 1);
+    renderPassEncoder.end();
+  }
+
+  private ensureBindGroupExists(trailMapIn: GPUTexture) {
+    if (this.previousTrailMapIn !== trailMapIn) {
+      this.bindGroup = this.device.createBindGroup({
+        layout: this.pipeline.getBindGroupLayout(0),
+        entries: [
+          {
+            binding: 0,
+            resource: this.device.createSampler({
+              magFilter: 'linear',
+              minFilter: 'linear',
+            }),
+          },
+          {
+            binding: 1,
+            resource: trailMapIn.createView(),
+          },
+        ],
+      });
+
+      this.previousTrailMapIn = trailMapIn;
+    }
+  }
+}