Consider exposing window size from Graphics2D

[matklad]

When drawing onto a resizable window, it's useful to know the current window size. Right now, I get it by storing the current size in my Handler and updating it on on_draw, but it would perhaps be more natural to have something like

impl Graphics2D {
    fn size(&self) -> Vec2;
}

Just so that one doesn't need to think about converting between integral pixels and float coordinates graphics is using for most stuff.

[dennisorlando]

Would #78 be a solution? It's not attached directly to Graphics2D but to the WindowHelper that gets passed with the draw() methods

[matklad]

Yup!

[QuantumBadger]

Now merged, thank you @dennisorlando!