When I use PGraphics, there is a strange overlap

LYY

LYY

Here is its program that can be run directly，No statement indicates that there will be traces outside PGraphics pg.

PGraphics pg;

void setup() {
  size(640, 360);
  pg = createGraphics(400, 200);
}

void draw() {
  fill(0, 12);
  rect(0, 0, width, height);
  fill(255);
  noStroke();
  ellipse(mouseX, mouseY, 60, 60);

  pg.beginDraw();
  pg.background(51);
  pg.noFill();
  pg.stroke(255);
  pg.ellipse(mouseX-120, mouseY-60, 60, 60);
  pg.endDraw();

  // Draw the offscreen buffer to the screen with image() 
  image(pg, 120, 60); 
}

jeremydouglass

there will be traces outside PGraphics pg

What do you mean? You are drawing a normal ellipse at the mouse coordinates on the line after noStroke. That will of course create traces outside pg

Also, because you never call background() the main sketch window never complete clears -- you are using repeatedly applying a very low alpha black text.