bug#63187: 30.0.50; Tail of longer lines painted after end of nearby lines on macOS

[Kai Ma]

> On Jun 9, 2023, at 01:22, Alan Third <alan@idiocy.org> wrote:
> 
> On Thu, Jun 08, 2023 at 10:57:43PM +0800, Kai Ma wrote:
>> 
>> 
>>> On Jun 8, 2023, at 21:42, Kai Ma <justksqsf@gmail.com> wrote:
>>> 
>>> 
>>>> On Jun 8, 2023, at 20:51, Alan Third <alan@idiocy.org> wrote:
>>>> 
>>>> I've got two things it could be worth trying to see if they make any
>>>> difference.
>>>> Change the CACHE_MAX_SIZE to something greater than 2, probably 4 is a
>>>> good number. That would rule out some sort of locking problem, as it
>>>> would reduce the chance a surface would be re-used before it's been
>>>> sent to the screen.
>>>> 
>>>> The downside of this is probably going to be an increase in "lag"
>>>> because it's possible to have more surfaces "in-flight".
>>>> 
>>>> The other option is to remove this call (nsterm.m:10636):
>>>> 
>>>> /* Schedule a run of getContext so that if Emacs is idle it will
>>>>   perform the buffer copy, etc.  */
>>>> [self performSelectorOnMainThread:@selector (getContext)
>>>>                       withObject:nil
>>>>                    waitUntilDone:NO];
>>>> 
>>>> I think this is harmless, but it's in there as I *assume*, with
>>>> absolutely no proof, that it will improve performance and it seems
>>>> possible (but I think unlikely) that it may affect the sequencing of
>>>> surface operations.
>>> 
>>> Tested locally. I can confirm that removing
>>> performSelectorOnMainThread (with CACHE_MAX_SIZE = 2) fixes the
>>> problem for me. I now observe zero glitches or tearings!
>>> 
>> 
>> Sorry, I concluded too fast. I can still see tearings, though very
>> rarely. So this is still not a real fix. :-(
> 
> Try increasing CACHE_MAX_SIZE too. Tearing would, I believe, be
> because a surface is being reused while it's still being copied to the
> VRAM, so you'll see a partially modified output.
> 
> If increasing CACHE_MAX_SIZE fixes it then there are a couple of
> possible options we can look at.

Increasing CACHE_MAX_SIZE alone doesn’t seem to help much.
(Screencast: https://www.youtube.com/watch?v=9YD9jyP-GKw)

Increasing CACHE_MAX_SIZE + Removing performSelectorOnMainThread seems to be 
better but I can’t be sure.  Just observed: 

(1) M-< at the mid of a buffer, but only the first line of the view is 
refreshed, and other parts were still there.

(2) selecting a region doesn’t always clear the hl-line effect.