bug#30699: 26.0.91; buffer contents flicker on macOS frames when frames are resized

[Alan Third]

On Fri, Mar 09, 2018 at 11:24:15PM +0000, Alan Third wrote:
> The other solution I have is to use NSDisableScreenUpdates to prevent
> updates being flushed to the screen until after redisplay, but that
> completely breaks resizing with the mouse.

I just realised that this isn’t actually hard to get right.

Patch attached. I think this is a better solution than the last one.

Disabling screen updates just stops them being flushed to the screen,
when they’re enabled all the updates happen at once (including the
window manager’s frame resize). I guess it’s like drawing to an
off‐screen buffer then swapping.
-- 
Alan Third

0001-Fix-frame-resize-flicker-on-macOS-bug-30699.patch
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