cairo/canvas.go
func (v *Context) MaskSurface(surface *Surface, surfaceX, surfaceY float64) {
	C.cairo_mask_surface(v.native(), surface.native(), C.double(surfaceX),
		C.double(surfaceY))
}
func (v *Context) MaskSurface(surface *Surface, surfaceX, surfaceY float64) {
	C.cairo_mask_surface(v.native(), surface.native(), C.double(surfaceX),
		C.double(surfaceY))
}
// TODO(jrick) Mask (depends on Pattern)
// MaskSurface is a wrapper around cairo_mask_surface().