Re: Looking up fonts and shapers in Pango

[Owen Taylor <otaylor redhat com>]

hashao <hashao@telebot.com> writes:

> Hello Owen,
> 
> Friday, January 21, 2000, 5:40:52 AM, you wrote:
> ...
> OT>  - Choosing a font for each character.
> OT>  - Choosing a shape engine for each character (handles conversion of 
> OT>    characters into font-specifc glyphs)
> 
> ...
> OT> The other approach that I've thought of for handling the font-coverage
> OT> problem is to simply punt the procedure to the installation process.
> 
> OT> That is, to assume that the person/vendor that is setting up system
> OT> fonts, and also the person distributing 3rd party fonts have good
> OT> knowledge of what shapers will be available. For instance, somebody
> OT> installing an X font encoded as tscii-0 assumes that a Tamil shaper is
> OT> available and then claims the coverage range for the font is
> OT> U+0B80 - U+0B8F, and installs some appropriate line in a global
> OT> configuration file.
> 
> OT> The worry I have with the second approach is that it means that the
> OT> font installation process has to be very tightly coupled to Pango,
> OT> and while I hope that Pango will be very widely used, a high level
> OT> installation complexity would hinder that process.
> 
> Pango could just maintain a coverage table/database itself. Each time
> it is called, it just check if there are new fonts not included in
> its database before doing the lookup stuff. If there are new
> fonts/shapers or removed fonts/shapers, the database should be
> updated. There are normally fewer fonts being added in a system after
> installation, so setting up a coverage table for new fonts should not
> be too slow. Beside, it is a one time process for each font.

Yes - this is basically what I meant by caching the results when I
described my first brute-force approach. 

There are definitely issues you have to worry about:

 - locking
 - knowing when fonts/shapers have been removed
 - providing feedback to the user during time-intensive operations.

   (You don't want every GTK+ program on your system to inexplicably lock
   up for 30 seconds when you install the Tamil shaper package.)

But it is a very reasonable approach.

Thanks for the input,
                                                  Owen