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

[Eli Zaretskii]

> From: Aaron Jensen <aaronjensen@gmail.com>
> Date: Mon, 1 May 2023 09:47:50 -0400
> Cc: Po Lu <luangruo@yahoo.com>, Alan Third <alan@idiocy.org>, 
> 63187@debbugs.gnu.org
> 
>   {
>     NSRect srcRect = NSMakeRect (x, from_y, width, height);
>     NSPoint dest = NSMakePoint (x, to_y);
>     EmacsView *view = FRAME_NS_VIEW (f);
> 
>     [view copyRect:srcRect to:dest];
> #ifdef NS_IMPL_COCOA
>     [view setNeedsDisplayInRect:srcRect];
> #endif
>   }
> 
> Why is the source being marked for redisplay? I would expect the
> destination to be marked as such, or am I missing something?

IMO, both should be marked for redisplay.  Or maybe I don't understand
the significance of marking a rectangle for redisplay.