func (gc *GraphicContext) newMask(x, y, width, height int) *Mask {
	mask := &Mask{}
	mask.X = float64(x)
	mask.Y = float64(y)
	mask.Width = toSvgLength(float64(width))
	mask.Height = toSvgLength(float64(height))

	// attach mask
	gc.svg.Masks = append(gc.svg.Masks, mask)
	mask.Id = "mask-" + strconv.Itoa(len(gc.svg.Masks))
	return mask
}
func (gc *GraphicContext) newMask(x, y, width, height int) *Mask {
	mask := &Mask{}
	mask.X = float64(x)
	mask.Y = float64(y)
	mask.Width = toSvgLength(float64(width))
	mask.Height = toSvgLength(float64(height))

	// attach mask
	gc.svg.Masks = append(gc.svg.Masks, mask)
	mask.Id = "mask-" + strconv.Itoa(len(gc.svg.Masks))
	return mask
}
// creates new mask attached to svg