paletteswap.glsl

uniform sampler2D swapTexture;
uniform bool shaderIsActive;

void main()
{
  vec4 pixel = texture2D(bitmap, openfl_TextureCoordv);

  if (!shaderIsActive)
  {
    gl_FragColor = pixel;
    return;
  }
      
  vec2 index = vec2(pixel.r, pixel.g);
  vec4 swapPixel = texture2D(swapTexture, index);

  if(pixel.a != 0.0 && swapPixel.a != 0.0) {
    pixel = swapPixel;
  }

  gl_FragColor = pixel;
}