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

[Po Lu]

Alan Third <alan@idiocy.org> writes:

> Po Lu asks about how it synchronises with the system, and it doesn't
> really have to. The system draws into the same buffer that copyRect
> accesses. It does make me wonder if there's a rare occasion when
> copyRect is called and the system hasn't flushed all it's drawing
> instructions to the buffer yet. It's probably possible to force it to
> flush by doing something like:
>
>     [[NSGraphicsContext currentContext] flushGraphics];
>
> at the top of copyRect. Preferably only on macOS 10.14 and above, but
> it probably makes no difference on other platforms since scrollRect
> should force a flush anyway.

Hmm... Aaron, could you try that?

BTW, I've just noticed that ns_scroll_run invalidates the source
rectangle, not the destination.  Shouldn't things be the other way
around?  I see Aaron saw that as well.