On Sun, Mar 04, 2018 at 08:27:36PM +0000, Alan Third wrote:
> On Sun, Mar 04, 2018 at 09:38:27AM -0800, Aaron Jensen wrote:
> > It appears that (on macOS, at least) when a frame is resized, there is
> > an unsightly flicker. It does not matter if the frame is undecorated or
> > not.
> 
> Simpler repro:
> 
> (dotimes (n 10)
>   (set-frame-parameter nil 'width (+ 80 n))
>   (sit-for 0.1))
> 

It’s the call to SET_FRAME_GARBAGED in EmacsView::updateFrameSize. I
don’t know if it’s needed in this circumstance, but without it it
stops the frame being blanked when resizing with the mouse, which is
unpleasant.

The attached patch appears to fix it without breaking mouse resizing,
but it looks like this comment in windowDidResize also counts for macOS:

   /* In GNUstep, at least currently, it's possible to get a didResize
      without getting a willResize.. therefore we need to act as if we got
      the willResize now */

I honestly don’t see that it makes any difference though.

The root problem is actually that we’re unable to execute redisplay
while the frame is being resized by a mouse. The NS event loop goes
into some ‘modal’ state which we can’t break out of, thus preventing
us from doing anything until it’s done. If that didn’t happen we
wouldn’t need to blank the screen at all.
-- 
Alan Third