Converts a p5js graphics object to an Image object. This way you can use an off screen buffer to create image masks.

sketch.js

function graphicsToImage(graphics){
  var img = createImage(graphics.width, graphics.height);
  img.loadPixels();
  graphics.loadPixels();
    for(var x = 0; x < img.width; x++){
      for(var y = 0; y < img.height; y++){
        idx = 4 * (y * img.width + x);
        img.pixels[idx] = graphics.pixels[idx];
        img.pixels[idx+1] = graphics.pixels[idx+1];
        img.pixels[idx+2] = graphics.pixels[idx+2];
        img.pixels[idx+3] = graphics.pixels[idx+3];
      }
    }
  img.updatePixels();
  return img;
}