cairo/canvas.go
func (v *Context) Rectangle(x, y, w, h float64) {
	C.cairo_rectangle(v.native(), C.double(x), C.double(y), C.double(w), C.double(h))
}
func (v *Context) Rectangle(x, y, w, h float64) {
	C.cairo_rectangle(v.native(), C.double(x), C.double(y), C.double(w), C.double(h))
}
// Rectangle is a wrapper around cairo_rectangle().