Add frame_x_center/frame_y_center variables for themes

Sometimes you want to position something (usually the title) to be centered
with respect to the entire frame instead of centered with respect to the
individual piece currently being drawn.

This patch adds frame_x_center and frame_y_center variables that represent
the X/Y centers of the frame in the coordinate system of the piece being
drawn.

The theme version is bumped from 3.0 to 3.1 (3.0 is just the new version
system, 3.1 will have all the features we add for Mutter-2.28.)
position expressions

https://bugzilla.gnome.org/show_bug.cgi?id=591842

NOTE: Patch is copied from mutter and is adapted for metacity.

doc/theme-format.txt

@@ -22,6 +22,16 @@ 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 3.1
+========================================
+
+Additional predefined variables are added for positioning expressions:
+
+  frame_x_center: the X center of the entire frame, with respect to the
+      piece currently being drawn.
+  frame_y_center: the Y center of the entire frame, with respect to the
+      piece currently being drawn.
+
 New Features in Theme Format Version 3
 ======================================
 

src/ui/theme-parser.c

@@ -38,7 +38,7 @@
  * look out for.
  */
 #define THEME_MAJOR_VERSION 3
-#define THEME_MINOR_VERSION 0
+#define THEME_MINOR_VERSION 1
 #define THEME_VERSION (1000 * THEME_MAJOR_VERSION + THEME_MINOR_VERSION)
 
 #define MARCO_THEME_FILENAME_FORMAT "metacity-theme-%d.xml"

src/ui/theme.c

@@ -2312,6 +2312,10 @@ pos_eval_get_variable (PosToken                  *t,
         *result = env->title_width;
       else if (t->d.v.name_quark == env->theme->quark_title_height)
         *result = env->title_height;
+      else if (t->d.v.name_quark == env->theme->quark_frame_x_center)
+        *result = env->frame_x_center;
+      else if (t->d.v.name_quark == env->theme->quark_frame_y_center)
+        *result = env->frame_y_center;
       else
         {
           g_set_error (err, META_THEME_ERROR,
@@ -2353,6 +2357,10 @@ pos_eval_get_variable (PosToken                  *t,
         *result = env->title_width;
       else if (strcmp (t->d.v.name, "title_height") == 0)
         *result = env->title_height;
+      else if (strcmp (t->d.v.name, "frame_x_center") == 0)
+        *result = env->frame_x_center;
+      else if (strcmp (t->d.v.name, "frame_y_center") == 0)
+        *result = env->frame_y_center;
       else
         {
           g_set_error (err, META_THEME_ERROR,
@@ -3485,13 +3493,17 @@ fill_env (MetaPositionExprEnv *env,
       env->right_width = info->fgeom->right_width;
       env->top_height = info->fgeom->top_height;
       env->bottom_height = info->fgeom->bottom_height;
+      env->frame_x_center = info->fgeom->width / 2 - logical_region.x;
+      env->frame_y_center = info->fgeom->height / 2 - logical_region.y;
     }
   else
     {
       env->left_width = 0;
       env->right_width = 0;
       env->top_height = 0;
       env->bottom_height = 0;
+      env->frame_x_center = 0;
+      env->frame_y_center = 0;
     }
 
   env->mini_icon_width = info->mini_icon ? gdk_pixbuf_get_width (info->mini_icon) : 0;
@@ -5047,6 +5059,8 @@ meta_theme_new (void)
   theme->quark_icon_height = g_quark_from_static_string ("icon_height");
   theme->quark_title_width = g_quark_from_static_string ("title_width");
   theme->quark_title_height = g_quark_from_static_string ("title_height");
+  theme->quark_frame_x_center = g_quark_from_static_string ("frame_x_center");
+  theme->quark_frame_y_center = g_quark_from_static_string ("frame_y_center");
   return theme;
 }
 

src/ui/theme.h

@@ -830,6 +830,8 @@ struct _MetaTheme
   GQuark quark_icon_height;
   GQuark quark_title_width;
   GQuark quark_title_height;
+  GQuark quark_frame_x_center;
+  GQuark quark_frame_y_center;
 };
 
 struct _MetaPositionExprEnv
@@ -845,6 +847,8 @@ struct _MetaPositionExprEnv
   int bottom_height;
   int title_width;
   int title_height;
+  int frame_x_center;
+  int frame_y_center;
   int mini_icon_width;
   int mini_icon_height;
   int icon_width;