changeColorPanel.pde

int circleX, circleY;

void setup() {
  size(500, 500);
  circleX = width/2;
  circleY = height/2;
}

void draw() {
  background(-1);
  ellipse(circleX, circleY, 200, 200);

  panel(mouseX, mouseY);
}

void panel(int pgX, int pgY) {
  PGraphics pg = createGraphics(200, 200);

  pg.beginDraw();
  pg.background(0);
  pg.fill(255, 0, 0);
  pg.ellipse(circleX - pgX, circleY - pgY, 200, 200);
  pg.endDraw();

  image(pg, pgX, pgY);
}