uniform shader image;
uniform float2 imageSize;
uniform float side;
half4 main(float2 coord) {
  float2 uv = coord / imageSize;
  if (side == 0) {
    if (uv.x > 0.5)
      uv.x = 1.0 - uv.x;
  } else if (side == 1) {
    if (uv.x < 0.5)
      uv.x = 1.0 - uv.x;
  } else if (side == 2) {
    if (uv.y > 0.5)
      uv.y = 1.0 - uv.y;
  } else if (side == 3) {
    if (uv.y < 0.5)
      uv.y = 1.0 - uv.y;
  }
  uv *= imageSize;
  return image.eval(uv);
}