uniform shader image;
uniform float angle;
uniform float scale;

half4 main(float2 coord) {
  float4 color = unpremul(image.eval(coord));
  float average = (color.r + color.g + color.b) / 3.0;
  float s = sin(angle), c = cos(angle);
  float2 point = float2(c * coord.x - s * coord.y, s * coord.x + c * coord.y) * scale;
  float pattern = (sin(point.x) * sin(point.y)) * 4.0;
  float4 result = float4(float3(average * 10.0 - 5.0 + pattern), color.a);
  result.rbg *= result.a;
  return result;
}