mask {
  source: color {
    bounds: 0 0 30 30;
    color: rgb(255,0,0);
  }
  mask: color {
    bounds: 15 15 30 30;
    color: rgb(255,255,255);
  }
}
mask {
  mode: inverted-alpha;
  source: color {
    bounds: 50 0 30 30;
    color: rgb(0,255,0);
  }
  mask: color {
    bounds: 65 15 30 30;
    color: rgb(255,255,255);
  }
}
mask {
  mode: luminance;
  source: color {
    bounds: 0 50 30 30;
    color: rgb(255,255,0);
  }
  mask: color {
    bounds: 15 65 30 30;
    color: rgb(255,255,255);
  }
}
mask {
  mode: inverted-luminance;
  source: color {
    bounds: 50 50 30 30;
    color: rgb(0,0,255);
  }
  mask: color {
    bounds: 65 65 30 30;
    color: rgb(255,255,255);
  }
}