code: func clearCanvas(canvas *xgraphics.Image, win *xwindow.Window) {
  	log.Println("Clearing canvas...")
  	canvas.For(func(x, y int) xgraphics.BGRA {
  		return bg
  	})
  
  	canvas.XDraw()
  	canvas.XPaint(win.Id)
  }
docs: // clearCanvas erases all your pencil marks.