Re: Error during redisplay

[David Kastrup <dak@gnu.org>]

Kenichi Handa <handa@m17n.org> writes:

> In article <85ir0aubo1.fsf@lola.goethe.zz>, David Kastrup <dak@gnu.org> writes:
>
>> Since the same string can be displayed with different fonts
>> simultaneously, this would look like a fault in the design.  The
>> composition property/whatever apparently needs to be associated with
>> the actual display, not just the string.
>
> In such a case, the composition property is generated each
> time.  The same situation happens when you display the same
> portion of a buffer in two frames with different fonts.
>
> It may result in a little bit slower redisplay.  If such a
> situation happens often and the slowness is so painful,
> perhaps the composition property must be an alist of fonts
> vs the current value.  It's not that difficult to implement.

I still think it wrong to change the text according to where it is
displayed.  This would appear to call at most for overlays (which can be
window specific and where changing them does not change the underlying
text).  So this sort of information probably belongs in the glyph matrix
or whatever it is called.

As far as I know, text properties are also subject to undo treatment.
It just makes me queasy to think about this.

> So, another way is to re-design the current redisplay engine
> to generate a composition glyph every time just by calling C
> functions.  I think it's an interesting experiment.

Sounds more like "sane" than "an interesting experiment" to me.  But on
the other hand, I have no relevant experience or knowledge whatsoever.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum