Re: [emacs-unicode-2] Segmentation fault 0x081b3df2 in xftfont_draw

[Kenichi Handa]

In article <address@hidden>, Leo <address@hidden> writes:

> It happens usually when there are many links in a buffer such as in ERC
> or W3M. I can move around mouse in a w3m buffer with tons of links (such
> as www.6park.com) to catch a crash, which usually happens within a few
> minutes. I just catch one with 'emacs -Q'. Unfortunately I don't know
> the exact recipe to trigger a crash.

I've just installed w3m and emacs-w3m, visited
www.6park.com, moved mouse-cursor and normal cursor onto
various links, but couldn't trigger a crash.

> The following can help you see the bug although it won't crash Emacs:

>          o  emacs -Q --enable-font-backend -fn SOMEFONT
>          o  C-u 3 2 M-x hanoi

> You should see the frame flickering like TV disturbed by static.

I can confirm the flickering with some fonts of some size.
For instance, this cause flickering:

emacs-unicode --enable-font-backend -fn 'dejavu sans mono:pixelsize=16'

but these don't cause flickering:

emacs-unicode --enable-font-backend -fn 'dejavu sans mono:pixelsize=24'
emacs-unicode --enable-font-backend -fn 'lucidatypewriter:pixelsize=16'

I think the reason is that font-height of "dejavu sans
mono:pixelsize=16" is somehow shorter than the glyph '|' in
that font.  So, every time Emacs redraw '|', the upper and
lower lines are also redrawn which leads to the whole buffer
redrawing.  For instance, when I replace all occurence of
"?\|" in lisp/play/hanoi.el with "?i", even this:

emacs-unicode --enable-font-backend -fn 'dejavu sans mono:pixelsize=16'

stops flickering.

Perhaps we must do something like this:

o When we open a font for a frame, check the ascents and
  descents of ASCII characters (perhaps checking only "\|/"
  is ok), and set font's ascent and descent to the maximum
  of them if the font's data is shorter than glyphs' data.

---
Kenichi Handa
address@hidden