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.