Using PGraphics to create a mask

Processing.py
2

Is this helpful? (sorry – just realised this is supposed to be Processing.py)

PGraphics main, mask;

void setup() {
  size(600, 600, P2D);
  main = createGraphics(width, height, P2D);
  mask = createGraphics(width, height, P2D);
}

void draw() {
  background(0);
  updateMask();
  updateMain();
  // apply mask
  main.mask(mask);
  image(main, 0, 0);
}

void updateMain() {
  main.beginDraw();
  main.background(128, 0, 0);
  main.stroke(255);
  main.strokeWeight(50);
  main.strokeCap(SQUARE);
  float y = noise(frameCount*0.01)*height;
  main.line(0, y, width, y);
  main.endDraw();
}

void updateMask() {
  mask.beginDraw();
  mask.background(0);
  mask.fill(255);
  float s = noise(frameCount*0.013);
  mask.ellipse(mask.width/2, mask.height/2, mask.width*s, mask.height*s);
  mask.endDraw();
}