func clearRect(gc *GraphicContext, x1, y1, x2, y2 float64) {
	// save state
	f := gc.Current.FillColor
	x, y := gc.pdf.GetXY()
	// cover page with white rectangle
	gc.SetFillColor(white)
	draw2dkit.Rectangle(gc, x1, y1, x2, y2)
	gc.Fill()
	// restore state
	gc.SetFillColor(f)
	gc.pdf.MoveTo(x, y)
}
func clearRect(gc *GraphicContext, x1, y1, x2, y2 float64) {
	// save state
	f := gc.Current.FillColor
	x, y := gc.pdf.GetXY()
	// cover page with white rectangle
	gc.SetFillColor(white)
	draw2dkit.Rectangle(gc, x1, y1, x2, y2)
	gc.Fill()
	// restore state
	gc.SetFillColor(f)
	gc.pdf.MoveTo(x, y)
}
// clearRect draws a white rectangle