sclass ImageSurfaceScribbleTool extends ImageSurfaceMouseHandler {
  settable BasicStroke stroke = new BasicStroke(5);
  settable Color color = Color.black;
  settable bool enabled;
  Pt lastPt;
  event painted;
  event scribbleDone(Scribble scribble);
  
  Scribble scribble;

  *() {}
  *(ImageSurface is) { this.register(is); }

  public void mousePressed(MouseEvent evt) {
    if (evt.getButton() != MouseEvent.BUTTON1) ret;
    if (!enabled) ret;
    lastPt = getPt(evt);
    scribble = new Scribble(color, stroke.getLineWidth(), new L);
    drawPoint(lastPt);
  }

  public void mouseReleased(MouseEvent e) {
    mouseDragged(e);
    lastPt = null;
    scribbleDone(scribble);
    scribble = null;
  }
  
  public void mouseDragged(MouseEvent e) {
    if (lastPt == null) ret;
    Pt p = getPt(e);
    if (!eq(p, lastPt))
      drawLine(lastPt, p);
    lastPt = p;
    is.repaint(); // That's gonna be slow...
  }
  
  void drawPoint(Pt p) {
    drawLine(p, p);
  }
  
  void drawLine(Pt a, Pt b) {
    scribble?.addPoint(b);
    Graphics2D g = getImageSurface().getImage().createGraphics();
    g.setStroke(stroke);
    g.setColor(color);
    g.drawLine(a.x, a.y, b.x, b.y);
    g.dispose();
    painted();
  }
}

Began life as a copy of #1005517