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

[Alan Third]

On Sat, Jun 24, 2023 at 09:34:18AM -0400, Aaron Jensen wrote:
> 
> Could you try removing the destination lock as well and see if that
> impacts anything? From what I can tell, locking the destination may be
> a good idea, but I'm curious if Alan has any thoughts as to why it'd
> be a bad idea.

copyContentsTo is only called by getContext, which has already locked
the destination, so there's no need to lock it again.

As I recall locking is really just setting a flag saying it's
currently being used so nobody else should touch it, it doesn't stop
you from doing things with it.

I know, for example, that it's possible to write to a surface that's
been locked by the transfer to VRAM, and that results in tearing
effects where the copy in VRAM is half updated. The VRAM copy isn't
ever copied back down to system RAM, though, so it doesn't have any
permanent consequences beyond a tearing effect at that particular
moment.
-- 
Alan Third