// Internal shader used to copy between two textures
      @group(0) @binding(0) var source: texture_2d<f32>;

      struct VertexOut {
        @builtin(position) pos: vec4f,
        @location(0) uv: vec2f,
      }

      @vertex fn vert_main(@builtin(vertex_index) vertexIndex : u32) -> VertexOut {
          var pos = array<vec2f, 3>(
              vec2f(-1.0, -1.0),
              vec2f( 3.0, -1.0),
              vec2f(-1.0,  3.0));
          return VertexOut(
            vec4f(pos[vertexIndex], 0.0, 1.0),
            vec2f(pos[vertexIndex].xy * vec2f(0.5, -0.5) + 0.5)
          );
      }

      @fragment fn frag_main(in: VertexOut) -> @location(0) vec4<f32> {
          let uv = vec2u(in.uv.xy * vec2f(textureDimensions(source)));
          return textureLoad(source, uv, 0);
      }