func (gc *GraphicContext) Clear() {
	width, height := gc.pdf.GetPageSize()
	clearRect(gc, 0, 0, width, height)
}
func (gc *GraphicContext) Clear() {
	width, height := gc.pdf.GetPageSize()
	clearRect(gc, 0, 0, width, height)
}
// Clear draws a white rectangle over the whole page