func (self *Surface) Mask(pattern Pattern) {
C.cairo_mask(self.context, pattern.pattern)
}
//Mask paints the current source using the alpha channel of pattern as a mask.
//Opaque areas of pattern are painted with the source, transparent areas are
//not painted.
//
//Originally cairo_mask.
func (c *Context) Mask(p Pattern) *Context {
C.cairo_mask(c.c, p.XtensionRaw())
return c
}