Subject: Re: bug#5977: 24.0.50; Lao HELLO is incorrectly displayed

From: Eli Zaretskii <[email-masked]>
Date: Sat, 24 Apr 2010 13:36:29 +0300

> Cc: [email-masked]
> From: Peter Dyballa <[email-masked]>
> Date: Sat, 24 Apr 2010 12:03:22 +0200
> 
> 
> Am 23.04.2010 um 20:31 schrieb Eli Zaretskii:
> 
> > I think I fixed this (revno 100013), please see if the problem is
> > solved for you.
> 
> 
> The GNU Emacs 24.0.50 with this fix still has problems with HELLO  
> (Bzr-100013 in mode-line). The Lao greetings are different depending  
> on whether the text cursor (point) is outside or inside the text strings:

How did you place the cursor there?  If by clicking the mouse, please
see whether the problem disappears if you move cursor there by
keyboard (C-f etc.).

In general, cursor motion problems with composed characters are a
different issue altogether.  However, on MS-Windows this particular
problem does not exist if I move cursor by keyboard commands.  And if
I move cursor by clicking the mouse, I can only change the shape of a
different character, the 6th one in the first word of the Lao
greeting.

> At the end of the visible characters the cursor jumps to a
> completely unexpected position: early in the session it was the end of
> the Braille "Hello" (with column-number-mode enabled I still saw line
> #44 and column #48) greeting, which later became visibly one line
> above (line ending character of the Bengali greeting) while mode-line
> still showed (44,48).

AFAICS, <RIGHT> at the last character on a line positions cursor at the
end of the first line displayed in the window.  This is part of the
cursor motion problems with composed characters.  This part _is_
visible on MS-Windows, and I'm working on it as we speak.

> When I click on the last but one character of the Lao greetings (44,
> 46) the second Thai greeting changes its shape...

Yes, I see that as well.

> The Arabic and Hebrew comments next to the Latin/English words  
> "Arabic" resp. "Hebrew" have two ")" and their greetings are not lined  
> up in a second (or right) column but touch the comments in parentheses.

That's yet another problem, which I actually mentioned in my message:
character composition does not yet work for text reordered for
display.  Out of all HELLO scripts, only Arabic and Hebrew are
reordered, and they use character compositions because the invisible
RLM character should be composed with the opening parenthesis that
follows it.

I will fix this eventually, but it is more urgent to fix problems in
L2R scripts that don't need reordering, because these are used by the
absolute majority of users.

> Clicking into the Braille "Hello" changes the Burmese greeting below  
> and the Burmese comment visibly... (normal first, clicked last)

The two images you sent display identically on my system, and I myself
cannot try this because I don't have a Burmese font installed (are
there good ones that are free?).

> Should I bug-report new Thai, Burmese, and Arabic/Hebrew HELLO bugs?

The bugs are not new.  You can file the bugs, but if you do, please
file 3 separate reports:

  . character composition doesn't work with bidi-reordered text
  . mouse clicking HELLO changes some characters
  . cursor motion incorrect at end of line that ends in a composite
    character

Thanks.