Re: macOS metal rendering engine in mac port

[Alan Third]

On Wed, Sep 15, 2021 at 09:30:09PM +0200, Illia Ostapyshyn wrote:
> Aaron Jensen <aaronjensen@gmail.com> writes:
> > It's infrequent, but I've seen a number of rendering artifacts in 28
> > in the last month or so. Typically it is a line of group of lines that
> > are painted twice (i.e. in the wrong place). I may see line 33
> > duplicated so there is no 34, just two 33 in a row. Scrolling to
> > change the position does not fix it. I have to scroll the buggy line
> > out of view entirely and scroll it back to get it to be right.
> >
> > I do not have a repro for this unfortunately.
> 
> I can confirm that I have been having this exact issue for quite some
> time now. It is very infrequent and mild so I never bothered to report
> it.
> 
> I also don't have any ideas what's causing it and how to reproduce it,
> but M-x redraw-display RET fixes it straight away.

If either of you do manage to come up with a recipe for reproducing
it, please let me know.

The most obvious candidate for incorrect duplication is in the
scrolling code. But since it's correct all the rest of the time there
would have to be something else forcing it.

Unless I just completely messed up the code in copyRect and it
sometimes copies lines of pixels in the wrong order, that can do
exactly what you're describing... But it works correctly practically
all the time, so it would have to be a rare edge case. 🤔
-- 
Alan Third