Re: font substitution

[Yen-Ju Chen]

On 8/5/07, Fred Kiefer <fredkiefer@gmx.de> wrote:
> Hi Rob,
>
> there was a reason why Alexander was reluctant at that time to add this
> patch to the main branch of GNUstep. This is a very expensive operation
> that we are doing for every change of a string and it isn't even optimised.
> I would kindly ask you to measure the time it take to perform text
> operations on a reasonable large file with and without this patch in
> place (Where all the characters are available in the assigned font).
> Only when we are sure this change wont slow GNUstep down too much,
> should we apply it. There are already some people complaining about the
> slowness of GNUstep and I don't want to make things harder for them.
>
> What would be even better is to come up with a highly optimized version
> of this patch. For example cache for all substitution fonts the
> supported character set and check that instead of creating each font in
> turn for each character that gets checked. Also the substitutions fonts
> should not come from a separate user setting instead we should take he
> preferred fonts first and if that fails check all available fonts (This
> can be really slow without a cache!). Another small optimisation could
> be to remember the last match and to try that font first the next time
> we are missing a character. And in the fixFontAttributeInRange: method
> we could get the characters more efficiently and reuse the same font for
> its effective range.
> The method used here to check if a font is valid for a character
> glyphForCharacter: is an extension that only exists for the art backend.
> We would need to replace it with coveredCharacterSet and implement that
> method for all backends.
>
> I really would love to integrate this patch and as you can see I spend
> some time thinking about it.

I think -coveredCharacterSet work mostly on art backend,
which use FreeType functions.
I believe the same thing can be done with Cairo by retrieving
FT_Face from cairo_scaled_font_t (?).
But for short term solution, if any of above-mentioned methods are
unavailable, ex in cairo backend, it can just fall back to do nothing
as current implementation.
I do meet some issues of -coveredCharacterSet with some fonts, though.

Yen-Ju

>
> Cheers
> Fred
>
> foobix@comcast.net wrote:
> > Quite some time ago Alexander Malmberg created a patch that gave
> > GNUstep font substitution capabilities. It has worked quite well.
> > Though, recent changes in GNUstep svn meant that the patch can no
> > longer be applied. I've manually applied his patch to svn (from a few
> > weeks ago), and created a new patch (attached). I was hoping this
> > could be commited to svn, so as to not become out of date again.
> >
>
>
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