[mutter] window: Add a hack to correct dragging from the top panel in gnome-shell

[Jasper St. Pierre <jstpierre src gnome org>]

commit 6fd1de226b6de3d9f8fd58066d233e940571a620
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Tue Aug 19 13:54:30 2014 -0400

    window: Add a hack to correct dragging from the top panel in gnome-shell
    
    In gnome-shell, we have a feature where the user can unmaximize windows
    by dragging them from the panel above the window. With accurate
    anchoring, this looks really weird as the cursor is now "detached" from
    the window. Detect this case and put the cursor in the middle of the
    window titlebar instead.

 src/core/window.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)
---
diff --git a/src/core/window.c b/src/core/window.c
index 3ab453e..b626a5d 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -5604,6 +5604,16 @@ update_move (MetaWindow  *window,
 
       display->grab_initial_window_pos.x = x - window->saved_rect.width * prop;
 
+      /* If we started dragging the window from above the top of the window,
+       * pretend like we started dragging from the middle of the titlebar
+       * instead, as the "correct" anchoring looks wrong. */
+      if (display->grab_anchor_root_y < display->grab_initial_window_pos.y)
+        {
+          MetaRectangle titlebar_rect;
+          meta_window_get_titlebar_rect (window, &titlebar_rect);
+          display->grab_anchor_root_y = display->grab_initial_window_pos.y + titlebar_rect.height / 2;
+        }
+
       window->saved_rect.x = display->grab_initial_window_pos.x;
       window->saved_rect.y = display->grab_initial_window_pos.y;