[mcclim-devel] Re: international text-style support

[Christophe Rhodes]

[ a very long time ago, in the context of supporting complicated
  international scripts ]
Gilbert Baumann <unk6 at rz.uni-karlsruhe.de> writes:

> Brian Spilsbury writes:
>  > I have implement (somewhat primitive) international text-style support.
>  > [...]
>
> This sounds like a somewhat reasonable design to me, although I would
> very much prefer if we could move the fontset logic into the frontend
> by coming up with a sort of font protocol.

So, now, we (at Goldsmiths) have a need for a specific font.  At the
moment, we have hacked in support to our application using
MAKE-DEVICE-FONT-TEXT-STYLE and some extreme hackiness in
CLIM-CLX::TEXT-STYLE-TO-X-FONT; the device-font-text-style support in
current CVS is ... not extensive, which is not really surprising given
that the spec is approximately equally non-extensive.

It tickled my memory, though, and I dug up this proposal:

> Something like this:
>
>   A font is a mapping from glyph names (indicies) to glyphs. Fonts
>   have additional attributes like name, weight, an encoding, a
>   language and so on. Glyphs have metrics and are drawable to
>   individual media. 
>
>   FONT                                                       protocol class
>
>   FONT-NAME font                                                     method
>   FONT-WEIGHT font                                                   method
>   FONT-SLANT font                                                    method
>   FONT-... font                                                      method
>
>     The individual typographical properties of the font.
>
>   SCALE-FONT font size -> font                                       method
>
>     Scales the font to a new size.
>     [Q1: Unit for size?]
>     [Q2: Should this affect metrics?]
>
>   FONT-SIZE font                                                     method
>
>     Returns the size of the font.
>
>   TRANSFORM-FONT font transformation -> font                         method
>
>     Applies a affine transformation to the font. Each glyph drawn with
>     the returned font are then drawn under the transformation. This
>     does not affect the individual glyph metrics.
>
>   FONT-TRANSFORMATION font -> transformation                         method
>
>     Returns the transformation of the font font.
>
>   FONT-GLYPH-METRICS font glyph                                      method
>                   -> width ascent descent left-bearing right-bearing
>
>     Returns the fonts glyph metrics. To calculate the metrics of
>     glyphs as drawn my draw-glyph the transformation of the font has
>     to be applied to the returned values.
>
>     [This is to keep the glyph-metrics as scalars instead of making
>     each metric into a vector].
>
>     width should not be negative in case of RTL script, since
>     typesetting from right to left is consided to be a property of a
>     text-style; likewise left-bearing bearing on the left hand side
>     as right bearing is bearing on the right hand size.
>
>     Q4: Is there something like top-bearing, bottom-bearing for fonts
>     designed towards top-to-bottom scripts?
>
>
>   FONT-KERNING font glyph-1 glyph-2                                  method
>
>     Returns the kerning to be applied when typesetting glyph-1 left of
>     glyph-2.
>
>   DRAW-GLYPH medium font glyph x y                                   method
>
>     [Q3: Interaction with general designs? Ideally we would make glyphs
>     into designs itself].
>
>   A text-style is a mapping of chracter sequences to font, glyph,
>   position triples for drawing. A text-style then might refer to
>   multiple fonts thus forming a fontset.
>
>   Each medium then knows its available fonts. These can be queried by
>   the frontend and combined into a text style.
>
> As you can see there are some questions and I am not entirely sure how
> things should really look like.

Nor am I.  I don't suppose anyone else has had thoughts in the last
three years?

We need: a way of specifying that we want to draw text using a
specific font (in our case, a FreeType font for tablature) at a
specific size.  If that's not a DEVICE-FONT-TEXT-STYLE, I don't know
where else it should go, but it does imply that a DEVICE-FONT has
size.

I'm away from my workstation, but tomorrow I'll send patches showing
what we're currently doing.

Cheers,

Christophe