cairo/canvas.go
func (v *Context) SetSourceSurface(surface *Surface, x, y float64) {
	C.cairo_set_source_surface(v.native(), surface.native(), C.double(x),
		C.double(y))
}
func (v *Context) SetSourceSurface(surface *Surface, x, y float64) {
	C.cairo_set_source_surface(v.native(), surface.native(), C.double(x),
		C.double(y))
}
// TODO(jrick) SetSource (depends on Pattern)
// SetSourceSurface is a wrapper around cairo_set_source_surface().