Re: Glyphs and the text system

[Alexander Malmberg]

BALATON Zoltan wrote:
[snip]
> What exactly is glyph generation? Is it the translation of character codes
> to glyph codes appropriate for the current font? Postscript uses encodings
> and functions provided by fonts for this. It would probably be a good idea
> to use something similar in the backend. Maybe there are already methods
> or a class in OpenStep to provide an interface to postscript encodings
> that the backend could implement with knowledge about a font, but I may be
> wrong as I have no time to check.

Glyph generation (in this context) means taking a sequence of abstract
(unicode) characters and turning them into a sequence of glyphs that
represent those characters, in some sense.

For latin scripts, this is easy, since one character can be mapped to
one glyph, but ligatures are a good example. Even when dealing with
normal english text, we want to use ligature glyphs for "ff", "fi",
"ffi" (ie. one glyph that represent both characters) if they are
available. Other scripts, like arabic and indic scripts, require a large
number of substitutions to draw correctly, often depending a lot on the
context of a character.

There are a couple of examples of substitutions here:
http://www.microsoft.com/typography/developers/opentype/over.htm

If we want even halfway-proper wysiwyg, printing will have to use the
same glyphs (with the same positioning and stuff) as the displayed
stuff. This isn't really a problem at the -gui level; it can just use
[NSGraphicsContext -GSShowGlyphs::]. Implementing it might be tricky,
though.

- Alexander Malmberg