theme: Allow using custom colors from the GTK+ theme

Add an additional color type to pick up colors defined with
@define-color in the GTK+ theme's CSS:

  gtk:custom(name,fallback)

(where "name" refers to the name defined in GTK+'s CSS, and fallback
refers to an alternative color spec which is used when the color
referenced by "name" is not found)

The main intent of the change is to allow designers to improve
Adwaita's dark theme variant without having to compromise on colors
which work in the light variant as well.

https://bugzilla.gnome.org/show_bug.cgi?id=648709

NOTE: Patch copied from mutter and adapted for metacity.

1 files changed, 12 insertions, 0 deletions

diff --git a/doc/theme-format.txt b/doc/theme-format.txt
index 79ef133f..31b47c4e 100644
--- a/doc/theme-format.txt
+++ b/doc/theme-format.txt
@@ -22,6 +22,18 @@ This document has separate sections for each format version. You may
 want to read the document in reverse order, since the base features
 are discussed under version 1.
 
+New Features in Theme Format Version 3.4
+========================================
+
+An additional color type is added to pick up custom colors defined
+in the GTK+ theme's CSS:
+
+  gtk:custom(name,fallback)
+
+where <name> refers to a custom color defined with @define-color in
+the GTK+ theme, and <fallback> provides an alternative color definition
+in case the color referenced by <name> is not found.
+
 New Features in Theme Format Version 3.3
 ========================================