uniform shader image;
uniform float2 imageSize;
uniform float scale;

float luma(float3 color) {
  return dot(color, float3(0.299, 0.587, 0.114));
}

half4 main(float2 coord) {
  
  float2 uv = coord / imageSize;
  uv.y = 1.0 - uv.y;

  float2 center = float2(0.5);
  float noiseScale = 1.;
  float radius = 0.5;
  float2 d = uv - center;
  float r = length(d * float2(1., imageSize.y / imageSize.x)) * scale;
  float a = atan(d.y, d.x) + noiseScale * (radius - r) / radius;
  float2 uvt = center + r * float2(cos(a), sin(a));

  float c = (.75 + .25 * sin(uvt.x * 1000.));
  float4 color = unpremul(image.eval(coord));
  float l = luma(color.rgb);
  float f = smoothstep(.5 * c, c, l);
  f = smoothstep(0., .5, f);
  float3 col = float3(f);

  return float4(col * color.a, color.a);
}