tiling: keep track of the monitor where a window was tiled

meta_window_get_current_tile_area() computes the area where the tiled window
should be based on the current pointer position but that's only meaningful
when the user is actually dragging the window.

When running the tiling constrain the pointer might be on other monitor and at
that point the window jumps to this other monitor.

https://bugzilla.gnome.org/show_bug.cgi?id=642580

src/core/display-private.h

@@ -189,6 +189,7 @@ struct _MetaDisplay
   int         grab_anchor_root_y;
   MetaRectangle grab_anchor_window_pos;
   MetaTileMode  grab_tile_mode;
+  int           grab_tile_monitor_number;
   int         grab_latest_motion_x;
   int         grab_latest_motion_y;
   gulong      grab_mask;

src/core/display.c

@@ -554,6 +554,7 @@ meta_display_open (void)
   the_display->grab_screen = NULL;
   the_display->grab_resize_popup = NULL;
   the_display->grab_tile_mode = META_TILE_NONE;
+  the_display->grab_tile_monitor_number = -1;
 
   the_display->grab_edge_resistance_data = NULL;
 
@@ -3593,9 +3594,15 @@ meta_display_begin_grab_op (MetaDisplay *display,
   display->grab_button = button;
   display->grab_mask = modmask;
   if (window)
-    display->grab_tile_mode = window->tile_mode;
+    {
+      display->grab_tile_mode = window->tile_mode;
+      display->grab_tile_monitor_number = window->tile_monitor_number;
+    }
   else
-    display->grab_tile_mode = META_TILE_NONE;
+    {
+      display->grab_tile_mode = META_TILE_NONE;
+      display->grab_tile_monitor_number = -1;
+    }
   display->grab_anchor_root_x = root_x;
   display->grab_anchor_root_y = root_y;
   display->grab_latest_motion_x = root_x;
@@ -3793,6 +3800,7 @@ meta_display_end_grab_op (MetaDisplay *display,
   display->grab_screen = NULL;
   display->grab_xwindow = None;
   display->grab_tile_mode = META_TILE_NONE;
+  display->grab_tile_monitor_number = -1;
   display->grab_op = META_GRAB_OP_NONE;
 
   if (display->grab_resize_popup)

src/core/keybindings.c

@@ -1612,6 +1612,7 @@ process_mouse_move_resize_grab (MetaDisplay *display,
 
       /* Restore the original tile mode */
       window->tile_mode = display->grab_tile_mode;
+      window->tile_monitor_number = display->grab_tile_monitor_number;
 
       /* End move or resize and restore to original state.  If the
        * window was a maximized window that had been "shaken loose" we

src/core/window-private.h

@@ -129,6 +129,7 @@ struct _MetaWindow
    * this is the current mode. If not, it is the mode which will be
    * requested after the window grab is released */
   guint tile_mode : 2;
+  int tile_monitor_number;
 
   /* Whether we're shaded */
   guint shaded : 1;

src/core/window.c

@@ -965,6 +965,7 @@ meta_window_new_with_attrs (MetaDisplay       *display,
   window->on_all_workspaces = FALSE;
   window->on_all_workspaces_requested = FALSE;
   window->tile_mode = META_TILE_NONE;
+  window->tile_monitor_number = -1;
   window->shaded = FALSE;
   window->initially_iconic = FALSE;
   window->minimized = FALSE;
@@ -4358,6 +4359,9 @@ meta_window_update_for_monitors_changed (MetaWindow *window)
         }
     }
 
+  if (window->tile_mode != META_TILE_NONE)
+    window->tile_monitor_number = new->number;
+
   /* This will eventually reach meta_window_update_monitor that
    * will send leave/enter-monitor events. The old != new monitor
    * check will always fail (due to the new monitor_infos set) so
@@ -5016,6 +5020,9 @@ meta_window_move_to_monitor (MetaWindow  *window,
                                          monitor,
                                          &new_area);
 
+  if (window->tile_mode != META_TILE_NONE)
+    window->tile_monitor_number = monitor;
+
   meta_window_move_between_rects (window, &old_area, &new_area);
 }
 
@@ -8431,11 +8438,15 @@ update_move (MetaWindow  *window,
       /* For side-by-side tiling we are interested in the inside vertical
        * edges of the work area of the monitor where the pointer is located,
        * and in the outside top edge for maximized tiling.
-       * Also see comment in meta_window_get_current_tile_area().
        *
        * For maximized tiling we use the outside edge instead of the
        * inside edge, because we don't want to force users to maximize
        * windows they are placing near the top of their screens.
+       *
+       * The "current" idea of meta_window_get_work_area_current_monitor() and
+       * meta_screen_get_current_monitor() is slightly different: the former
+       * refers to the monitor which contains the largest part of the window,
+       * the latter to the one where the pointer is located.
        */
       monitor = meta_screen_get_current_monitor (window->screen);
       meta_window_get_work_area_for_monitor (window,
@@ -8457,6 +8468,9 @@ update_move (MetaWindow  *window,
         window->tile_mode = META_TILE_MAXIMIZED;
       else
         window->tile_mode = META_TILE_NONE;
+
+      if (window->tile_mode != META_TILE_NONE)
+        window->tile_monitor_number = monitor->number;
     }
 
   /* shake loose (unmaximize) maximized or tiled window if dragged beyond
@@ -9271,17 +9285,18 @@ void
 meta_window_get_current_tile_area (MetaWindow    *window,
                                    MetaRectangle *tile_area)
 {
-  const MetaMonitorInfo *monitor;
+  int tile_monitor_number;
 
   g_return_if_fail (window->tile_mode != META_TILE_NONE);
 
-  /* The definition of "current" of meta_window_get_work_area_current_monitor()
-   * and meta_screen_get_current_monitor() is slightly different: the former
-   * refers to the monitor which contains the largest part of the window, the
-   * latter to the one where the pointer is located.
-   */
-  monitor = meta_screen_get_current_monitor (window->screen);
-  meta_window_get_work_area_for_monitor (window, monitor->number, tile_area);
+  tile_monitor_number = window->tile_monitor_number;
+  if (tile_monitor_number < 0)
+    {
+      meta_warning ("%s called with an invalid monitor number; using 0 instead\n", G_STRFUNC);
+      tile_monitor_number = 0;
+    }
+
+  meta_window_get_work_area_for_monitor (window, tile_monitor_number, tile_area);
 
   if (window->tile_mode == META_TILE_LEFT  ||
       window->tile_mode == META_TILE_RIGHT)