Macro rect 

macro_rules! rect {
    (x: $x:expr, y: $y:expr, w: $w:expr, h: $h:expr) => { ... };
    (pos: $pos:expr, size: $size:expr) => { ... };
}

create a Rect from components.

example

use lunar_math::rect;

let r = rect!(x: 0, y: 0, w: 100, h: 50);