Hello Gtk and hello Shell developers, In https://bugzilla.gnome.org/show_bug.cgi?id=687881 I promised I'd try to address one of the big performance problems in the current gnome-shell, which is the St theming system. Currently St does an awful lot of string matching again and again, as neither the style classes and element names, nor the property names are interned or preprocessed. We rely on libcroco to do basic tokenization, but that's it, everything else happens every time a StThemeNode (~ GtkStyleContext) is computed. We introduced some caching at the beginning of the 3.7 cycle, but to me that's just papering over a bad implementation. So I started to rewrite it. I streamlined selector matching, added quarking to classes, tried to normalize css values at parsing time and finally built a map of known CSS properties to StThemeNode fields. But I don't have a selector tree, I don't have GtkBitmask optimizations, I had to reimplement GtkCssValue, etc. The patch is not complete (it's missing background properties), but I'm thinking: why should I write this again? Someone else did this in Gtk, can't we just use that?
And this prompted me to this mail: is there a way for gnome-shell to reuse Gtk CSS implementation? Ideally, we would just use GtkStyleContext outside GtkWidget, and parts of Gtk's docs claim it is supported. But I'm curious on what assumptions are made from GtkWidgetPath, and if those assumptions can be worked around or lifted. Additionally, there are a number of accessors that are not exposed by GtkStyleContext or GtkThemingEngine, but are available only to Gtk internals. Consider that we can't use gtk_render_*, since we use Cogl for painting, not cairo. The next issue with that straightforward approach is that St's theming is slightly more powerul than Gtk's. Looking at the gtk docs, I see Gtk has no support for box-shadow, icon-shadow (st extension), background-position, background-size, outline, text-decoration, text-align, as well as width, min-width and max-width. If we were to use Gtk directly, we would need to move our implementation into Gtk, or work around that limitation. Also, I saw that Gtk has recently deprecated extension CSS properties. We use a number of those in gnome-shell, and it's not always possible to replace them with standard CSS2, although I guess it'd be possible to use gtk_style_context_save() / add_class() / restore() like Gtk themes do. The second option is to share just code, in some form, either as a private shared library that would be provided by Gtk (libgtk-internal?) and developed by both teams, or just as a copy-lib, with a massive s/Gtk/St/. I'm not sure what would be the cost of this last possibility, but I'm still convinced it would be lower than rewriting from scratch, and maintaining two different CSS implementations in GNOME. Looking forward to your comments, Giovanni _______________________________________________ gnome-shell-list mailing list gnome-shell-list@gnome.org https://mail.gnome.org/mailman/listinfo/gnome-shell-list
