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defining "virtual" fonts

    Date: Fri, 19 Apr 91 10:25:02 CDT
    From: George Williams <george@hsvaic.boeing.com>

    Is there an equivalent in CLIM 1.0 (I don't have CLIM yet, it's on
    order) to the Symbolics function si:define-character-style-families?
    I want to be able to define a font face name and family of styles, and
    have them mapped to "real" fonts (i.e., fonts that are installed on my
    machine).

Sure.  Depends exactly what you want to do, of course, as to what the right way
to do this.  Here are the primitives:

  (clim:define-text-style-mappings device character-set
	. style-specs)

will define the various style specifications for the given device.  The syntax is
pretty straightforward; see the source for GENERA-IMPLEMENTATION.LISP for a
simple example.

Of course, to use this you need to get the device object.  Once you have your root
window, you get it with CLIM::STREAM-DISPLAY-DEVICE-TYPE, but you can't use that
at load time, in general, because you don't want to create your root window just
by loading your software, so you probably shouldn't use DEFINE-TEXT-STYLE-MAPPINGS
(it's mostly for implementors of ports, where the implementor will put a display
device into a variable, like the Genera si:*b&w-device* or whatever it's called).

All is not lost, however.  There is a function named CLIM:ADD-TEXT-STYLE-MAPPING,
which takes a device, a character set, a text style and a font.  This function is
intended to use at runtime, after you have your streams in hand.  The device is
gotten as above.  The character set is probably CLIM:*STANDARD-CHARACTER-SET* (if
you have a non-standard character you can call CLIM::CHAR-CHARACTER-SET-AND-INDEX
on it, ignoring the second value).  [Character sets are currently ignored, but if
you want to continue to have working code in the future, you should use them.]
The text style must be a text style object, not a list.  The result can be a font
name or a cons (:STYLE . text-style), which is an "indirect style".

For example, you can do the following to a Genera-based window:

  (let ((device (clim::stream-display-device-type root)))
    (clim:add-text-style-mapping
      device clim:*standard-character-set*
      (parse-text-style '(:eurex :italic :huge)) 'fonts:eurex24i)
    (clim:add-text-style-mapping
      device clim:*standard-character-set*
      (parse-text-style '(:eurex :italic :normal)) 'fonts:eurex12i))

There is currently a bug in 1.0 for Genera whereby it doesn't load Genera screen
fonts automatically.  Alternatively, you can load the font yourself and pass in
the font itself instead of its name.

The CLX implementation requires that you pass in X font objects rather than names.
Unfortunately, getting font objects instead of font names requires that you have
the X display object in hand.  There is no advertised way to get this currently,
but you can get the CLIM::DISPLAY slot out of the root window.

I will put the fact that you can't give names instead of font objects to
ADD-TEXT-STYLE-MAPPING on the bug list, as well as the fact that you have to parse
text styles before passing them in to ADD-TEXT-STYLE-MAPPING.

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