Re: Theming API hackfest: last call

["Robert Staudinger" <robert staudinger gmail com>]

On Fri, Oct 10, 2008 at 3:36 AM, Behdad Esfahbod <behdad behdad org> wrote:

[...]

> Hi Rob,
>
> I got to know about work you are doing by crossing over your fd.o account
> request.  I thought to myself: "wow, this is so cool... why didn't I hear
> about this stuff before?"  I think a good number of GNOME/GTK+ developers are
> in that boat too.  So, why don't you tell us some more about what you've been
> doing and what your future plans are?  Here on the list I mean.

Sure.

It was some 2 years ago when I first toyed with CSS, gtk and engines,
but quickly lost interest because trying to parse gtkrc-embedded CSS
with GScanner was too much legwork. This summer I looked at the code
again but only after taking the time to read up on libcroco usage.
Basically, why did you not hear about it, well, it took some time to
get from the "it kinda does something" of the early prototypes to a
better understanding of the issues involved. I am confident that the
upcoming 0.3 release will be more suited to be shown off.

The main items of experimentation have been the intersection of
primitive- and widget-theming and the libccss API.

By "primitive theming" I am referring to direct influence on drawing
function calls. If you write "box { background: red; }" in your CSS,
the visual result of gtk_paint_box() calls will be affected.

"Widget-theming" on the other hand is applied to gtk's type names,
like e.g. the CSS statement "GtkButton { border: 1px solid black; }".
Internally a GtkButton is drawn using gtk_paint_box(), so both the
"primitive style" and the "widget style" have to be combined. The CSS
engine does so by merging the primitive style into the widget style
with a lowered priority, see also [1]. Things are not quite finished
for composite widgets like GtkComboBox, but there is a plan.

It soon became apparent that CSS drawing capability wrapped into a
simple API might be of use for other cairo-based applications as well,
so with some support from Carl Worth I spun that part off to fd.o
after the recent 0.2 release. Currently I'm focusing on the libccss
API, feedback from Intel's Robert Bragg and Thomas Wood has been very
valuable. After that I'll try to focus on the engine again, mostly the
support for composite widgets mentioned above.

I'll also be looking into setting style parameters from CSS, probably
something like "GtkButton { gtk: child-displacement-x(1); }" or
"GtkButton { gtk-child-displacement-x: 1; }".

Finally, regarding the SVG theming efforts that are floating around
[2, 3], I think that CSS and SVG are mostly orthogonal rather than
competing with each other. SVG is great for graphics, and CSS is made
for things like expressing that the GtkButton instance inside a
GtkTreeView should be drawn as a column header.

[1] http://www.w3.org/TR/CSS21/cascade.html#specificity
[2] http://groups.google.com/group/manju-project
[3] http://mail.gnome.org/archives/gnome-themes-list/2008-October/msg00001.html

Hope that helps a bit, I'd be happy to answer more specific questions,
or just find me on gimpnet.

- Rob