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

[Kai Ma]

> 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.  :-(