uniform shader image;
uniform float2 imageSize;
uniform float radius;
uniform float segments;
half4 main(float2 coord) {
  float2 uv = coord / imageSize;
  float2 normCoord = 2.0 * uv - 1.0;

  // to polar coords
  float r = length(normCoord);
  float phi = atan(normCoord.y, normCoord.x);

  r = r - mod(r, radius) + 0.03;
  phi = phi - mod(phi, segments);

  normCoord.x = r * cos(phi);
  normCoord.y = r * sin(phi);

  float2 textureCoordinateToUse = normCoord / 2.0 + 0.5;
  textureCoordinateToUse *= imageSize; 
  return image.eval(textureCoordinateToUse);
}