uniform shader image;
uniform float2 imageSize;
uniform float amount;
uniform float position;
half4 main(float2 coord) {
  float weights[5];
  weights[0] = 0.1633;
  weights[1] = 0.1531;
  weights[2] = 0.12245;
  weights[3] = 0.0918;
  weights[4] = 0.051;

  float vv = amount * abs((1 - position) * imageSize.y - coord.y);
  float4 sum = 0.1633 * image.eval(coord);
  for (int i = 1; i <= 4; i++) {
    float weight = weights[i];
    sum += weight * image.eval(coord - float2(0, float(i) * vv));
    sum += weight * image.eval(coord + float2(0, float(i) * vv));
  }
  return sum;
}