bug#38731: 27.0.50; Unexpected redisplay behaviour. Cursor can’t be moved to end of line.

[Alan Third]

On Thu, Dec 26, 2019 at 07:29:21PM +0200, Eli Zaretskii wrote:
> > Date: Thu, 26 Dec 2019 12:59:17 +0000
> > From: Alan Third <alan@idiocy.org>
> > Cc: HaiJun Zhang <netjune@outlook.com>, 38731@debbugs.gnu.org
> > 
> > In ns_draw_glyph_string I can see that s->x is correctly set to 136
> > when the backtrace doesn’t contain expose_frame, but 178 when it does.
> 
> Isn't it the other way around?  The correct display should start at a
> larger X coordinate.  Or maybe I don't understand what is s->x in this
> context, i.e. what glyph string is S.

Unless I’m somehow seeing a different problem (I haven’t watched the
video) the problem occurs when the buffer is scrolled horizontally,
and we should be able to see the end of the line point is on. However,
the line is drawn off the right side of the frame.

I’ve attached an image that I hope illustrates it better than I can
describe. You can see the glyph seen in the cursor is a /, and is the
first character of the text. The end of the line is at the b in
foobar.

So the text is drawn at too large an X coordinate, although the glyph
seen in the cursor is always correct.

Anyway, I’ll have a dig around and see if I can find where it’s going
wrong.

-- 
Alan Third

Screenshot 2019-12-27 at 14.25.18.png
Description: bug38731 screenshot