Subject: Re: OpenType (was Re: Yiddish in Abi?)
From: Andrew Dunbar (hippietrail@yahoo.com)
Date: Sat Jun 30 2001 - 08:30:27 CDT
Tomas Frydrych wrote:
>
> > Andrew:
> > Bidi isn't really ready for prime time on Windows. Windows uses all
> > kinds of funky OpenType magic to render nice Arabic script but AbiWord
> > is not doing all it can with font metrics.
>
> I think if we are serious about AW being multilingual, we need to
> consider OpenType; there are parts of Unicode that implicitely rely
> on the capabilities of OpenType and cannot be implemented with
> older font technologies.
>
> I recall that Leonard suggested repeatedly in the past that we
> consider using the FreeType rasteriser in AW, and I am more and
> more inclined to think that he is right about that, and that by relying
> on the rasterisers provided by the OS's (with their varied
> capabilities), we are giving ourselves lot of trouble.
I think we have two options though I admit to not understanding
the *nix situation fully yet. One options is to use FreeType
and the other option is to use Pango which uses Freetype. On
Windows we have TrueType already so much code should be 100%
portable I believe.
> > There are some strange results. Most noticeable
> > (for me) is when selecting text. The block shown as selected is
> > usually greater than that portion of text is rendered. The
> unselected
> > portion is rendered to the right of the selected block. The same
> > occurs for Thai and Idic scripts. And I don't think that's all ):
>
> The developers who initially wrote the code for calculating widths of
> strings assumed that all characters have positive width, i.e., no
> combining characters. To be fair to them, I think X has no means of
> coping with overstriking characters at all. The problem in handling
> these is that under X AW has to know that even though the
> character is reported as having a positive width, it is really
> overstriking and draw it in correct place (the mechanism for that is
> in place in the Unix bidi build, but the list of chars in
> ut_OverstrikingChars.cpp needs to be expanded); in contrast,
> under Windows this is taken care of by the font renderer, so that
> the text is drawn correctly; at the same time Win AW uses its own
> code to calculate the width of such a string counting each
> overstriking char as having a positive width, so that the width of the
> selection is greater than it should be.
Yes this really is the job of the renderer so FreeType or Pango
is really needed or we would have to implement a huge amount of
stuff to achieve the same goal with them. It would be nice if
we could keep a design that will work with and without this though
for people that only want to use western fonts and retain a small
footprint which I think is a fair call but means who knows how
much more work?
> What we have at the moment is platform-depenent mess. If we
> were using our own renderer, it would become a straighforward
> cross-platform issue.
Again I really think we should have OpenType rendering code
in the future since some platforms support it natively and
there is FreeType for the others. I think using FreeType on
Windows is possible but huge and pointless bloat.
Andrew.
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