draw2dpdf/gc.go
func (gc *GraphicContext) Rotate(angle float64) {
	gc.StackGraphicContext.Rotate(angle)
	gc.pdf.TransformRotate(-angle*180/math.Pi, 0, 0)
}
func (gc *GraphicContext) Rotate(angle float64) {
	gc.StackGraphicContext.Rotate(angle)
	gc.pdf.TransformRotate(-angle*180/math.Pi, 0, 0)
}
// Rotate rotates the following text, drawings and images.
// Angle is specified in radians and measured clockwise from the
// 3 o'clock position.
// This must be placed between gc.Save() and gc.Restore(), otherwise
// the pdf is invalid.