Re: about P1 part of BIDI alogrithm

From: Martin J. Dürst <>
Date: Tue, 11 Oct 2011 19:59:44 +0900

Hello Kent,

I was also very much thinking that mirrored glyph should be of the same
width, but there might be subtle issues when you consider kerning. As a
very basic example, think about kerning of the pair K), and then think
about K(.

Regards, Martin.

On 2011/10/11 19:39, Kent Karlsson wrote:
> Den 2011-10-11 09:43, skrev "Eli Zaretskii"<>:
>> Let me give you just one example: if the character should be mirrored,
>> you cannot decide whether it fits the display line until _after_ you
>> know what its mirrored glyph looks like. But mirroring is only
>> resolved at a very late stage of reordering, so if you want to reorder
>> _after_ breaking into display lines, you will have to back up and
>> reconsider that decision after reordering, which will slow you down.
> Well, I think there is a silent (but reasonable, I would say) assumption
> that mirroring does not change the width of a glyph... I would think that if
> a font does not fulfill that, then you have a font problem (or mix of fonts
> problem), not a bidi problem. Glyphs for characters that may mirror do not
> normally form ligatures with other glyphs; and even if they do, the width of
> the ligature should not change relative to the total with of the preligature
> glyphs involving glyphs for mirrorable characters (and if it does change
> anyway, you again have a font problem that may result in a somewhat ugly
> display that should be fixed by fixing the font, not a bidi problem). I'm
> not thinking about Emacs here, but in general.
> /Kent K
Received on Tue Oct 11 2011 - 06:03:27 CDT

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