macOS: (in window example) redundant redraw request during resizing #4517

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1. Random-Scientist

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   B - bugDang, that shouldn't have happenedDang, that shouldn't have happened

   DS - appkitAffects the AppKit/macOS backendAffects the AppKit/macOS backend

   on Mar 16, 2026
2. madsmtm commented on Mar 17, 2026

   

   madsmtm

   on Mar 17, 2026

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   Yup, I've recently found this too in rust-windowing/softbuffer#343 (comment).

   I'm still unsure of the right way to fix it - possibly drawRect: should just call window.request_redraw(), and not try to handle the redraw directly? I can't quite remember why we even try to, possibly to make resizing work more smoothly.
3. Random-Scientist commented on Mar 17, 2026

   

   Random-Scientist

   on Mar 17, 2026

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   Question is whether there is ever a case where we need to respect drawRect, to which I think the answer is no because all of the rendering is driven through the user anyways e.g. by SurfaceResized or the previous turn of a redraw loop
4. madsmtm commented on Mar 17, 2026

   

   madsmtm

   on Mar 17, 2026

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   See also #2640.

   I think I was originally motivated by #1605 that drawRect: + setNeedsDisplay was the right approach. I'm less convinced of this nowadays, I think there's a bunch of overhead from drawRect: that we'd rather avoid if we could (e.g. by setting wantsUpdateLayer instead).

   Ideally, I tend to think we should have like 3 different rendering modes that the user must choose between somehow:

   • Render on each frame, we schedule this using CADisplayLink (this is the only way to get 90 fps with ProMotion IIUC, drawRect: can't give you that).
   • Render only when request_redraw is called. Unsure when the best time to call this is? Definitely before about_to_wait (because stuff is sent to the compositor just before the end of the runloop (this is what causes Must call request_redraw in about_to_wait #4501)).
   • Render using drawRect: (to properly support drawing with CGContext).

   (Scattered thoughts, been a while since I looked into this).