Redrawing on macOS will not work with future versions of Winit

[madsmtm]

Winit currently implements redrawing in a weird ad-hoc fashion on macOS. This causes a bunch of issues, see https://github.com/rust-windowing/winit/issues/2640 for some of it, which I intend to fix by emitting RedrawRequested in the built-in scheduled draw events (-[NSView drawRect:] / -[NSView updateLayer]) instead.

However, this won't work when the "consumer" of the raw-window-handle that Winit provides (i.e. blade) is overriding the layer on NSView, as is currently done, since that makes the view "layer-hosting", see -[NSView wantsLayer].

The code in question is around here: https://github.com/kvark/blade/blob/5da73b1807079c5289613b652901e29169b6ffc7/blade-graphics/src/metal/surface.rs#L21-L63

To fix this, blade should be using -[CALayer addSublayer:] like on iOS instead of -[CALayer setLayer:]. The logic to get resizing to work automatically after this though is a bit cumbersome (you'll need to use observers), so I've extracted it into a crate: raw-window-metal.

I can submit a PR for it if you want, though note that raw-window-metal depends on objc2. If you don't want to use that, you could try to use a similar approach as wgpu currently does, though beware that that still has issues, observers are really the best way to do this (that I've found at least).

[kvark]

Interesting, thank you for bringing this up! So you are saying we shouldn't be replacing the layer, and we can add a sub-layer. If there is already a layer though, would it be fine to just use it directly (instead of a sublayer)?

[madsmtm]

Interesting, thank you for bringing this up! So you are saying we shouldn't be replacing the layer, and we can add a sub-layer. If there is already a layer though, would it be fine to just use it directly (instead of a sublayer)?

Yeah, if the view is already configured with a CAMetalLayer, you either have MTKView, and then resizing is going to work in a different way anyhow, or the user has overwritten -[UIView layerClass] on iOS / called setLayer: on macOS, in which case they're responsible for the view now being layer-hosting (so they're also responsible for letting blade know when to resize and redraw).