Re: OpenType Indic Support

[Eric Mader <mader jtcsv com>]

At 08:28 PM 12/19/2001, Owen Taylor wrote:

> Eric Mader <mader jtcsv com> writes:
>
> > Hello,
> >
> > I've got an OpenType based Indic shaper that I'm working on porting to
> > Pango.
>
> Great!
>
> > It's a single piece of code that's driven by a script-specific
> > table. Ideally, I'd like to have a single script_shape routine that's
> > called with the address of the table as a parameter, but it doesn't
> > look like there's any way to do that since the PangoEngine isn't a
> > parameter to the script_shape routine, and there's no provision for a
> > client-specific data pointer.
>
> Actually, the PangoEngine is passed in, though it may not
> be obvious how -- it's accessible as analysis->shape_engine.

Cool!

> > So, I'm guessing that the best I can can do is to make a bunch of
> > short script_shape routines that call the main routine with the right
> > table address. Have I missed something, or is this the best I can do?
>
> You can certainly create a structure that extends PangoEngineShape
> and adds an extra pointer, though whether this is easier than
> having small wrapper routines, I don't know.

Well, I'm porting from C++, so my initial inclination is to extend 
PangoEngineShape, but I may start with the wrappers 'cause it will be a bit 
easier to get that right the first time.

> > Also, I'm a little unclear on what the different types of shapers
> > are. I assume that mine should be an "xft" shaper like the Arabic
> > one. Can someone give me a pointer for where to look to hook in my new
> > shaper?
>
> The different types of shapers correspond to the different
> font engines in Pango -
>
>  PangoXft (rendering of client side fonts using Xft and the
>            XRENDER extension)
>  PangoFT2 (client side fonts, no reference to X)
>  PangoX   (old-style X bitmap fonts)
>  PangoWin32 (windows native fonts)
>
> Layout using OpenType is relevant to at least PangoXft
> and PangoFT2, and possibly PangoWin32 as well (though that's
> a bit different since it doesn't use FreeType to access the
> fonts), so I'd expect the core of your shaper to eventually
> be useful for multiple fontbackens.
>
> But for now, the OpenType support is only compiled into the
> Xft backend, and only the Xft backend has the necessary
> hooks to use it (though it would be pretty trivial to
> add to the FT2 backend.) So, copying the general way
> the arabic-xft is compiled and registers itself probably
> is the way to go.

OK, I'll copy the arabic-xft for now. Do I need to touch anything else to 
get my module to load?

> Regards,
>                                         Owen

Thanks,
Eric

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