x11: Add support for _GTK_EDGE_CONSTRAINTS atom

To keep feature parity with the Wayland backend, and
to improve the overall tiling experience with GTK apps,
add the _GTK_EDGE_CONSTRAINTS X11 atom and update it
when necessary.

https://bugzilla.gnome.org/show_bug.cgi?id=751857

src/core/constraints.c

@@ -943,7 +943,7 @@ constrain_maximization (MetaWindow         *window,
   /* Calculate target_size = maximized size of (window + frame) */
   if (META_WINDOW_TILED_MAXIMIZED (window))
     {
-      meta_window_get_current_tile_area (window, &target_size);
+      meta_window_get_tile_area (window, window->tile_mode, &target_size);
     }
   else if (META_WINDOW_MAXIMIZED (window))
     {
@@ -1030,7 +1030,7 @@ constrain_tiling (MetaWindow         *window,
   /* Calculate target_size - as the tile previews need this as well, we
    * use an external function for the actual calculation
    */
-  meta_window_get_current_tile_area (window, &target_size);
+  meta_window_get_tile_area (window, window->tile_mode, &target_size);
 
   /* Check min size constraints; max size constraints are ignored as for
    * maximized windows.

src/core/edge-resistance.c

@@ -556,7 +556,7 @@ apply_edge_resistance_to_each_side (MetaDisplay         *display,
 
   edge_data = display->grab_edge_resistance_data;
 
-  if (auto_snap)
+  if (auto_snap && !META_WINDOW_TILED_SIDE_BY_SIDE (window))
     {
       /* Do the auto snapping instead of normal edge resistance; in all
        * cases, we allow snapping to opposite kinds of edges (e.g. left
@@ -591,6 +591,50 @@ apply_edge_resistance_to_each_side (MetaDisplay         *display,
                                         FALSE,
                                         keyboard_op);
     }
+  else if (auto_snap && META_WINDOW_TILED_SIDE_BY_SIDE (window))
+    {
+      MetaRectangle workarea;
+      guint i;
+
+      const gfloat tile_edges[] =
+        {
+          1./4.,
+          1./3.,
+          1./2.,
+          2./3.,
+          3./4.,
+        };
+
+      meta_window_get_work_area_current_monitor (window, &workarea);
+
+      new_left = new_outer->x;
+      new_top = new_outer->y;
+      new_right = new_outer->x + new_outer->width;
+      new_bottom = new_outer->y + new_outer->height;
+
+      /* When snapping tiled windows, we don't really care about the
+       * x and y position, only about the width and height. Also, it
+       * is special-cased (instead of relying on edge_data) because
+       * we don't really care for other windows when calculating the
+       * snapping points of tiled windows - we only care about the
+       * work area and the target position.
+       */
+      for (i = 0; i < G_N_ELEMENTS (tile_edges); i++)
+        {
+          guint horizontal_point = workarea.x + floor (workarea.width * tile_edges[i]);
+
+          if (ABS (horizontal_point - new_left) < 16)
+            {
+              new_left = horizontal_point;
+              new_right = workarea.x + workarea.width;
+            }
+          else if (ABS (horizontal_point - new_right) < 16)
+            {
+              new_left = workarea.x;
+              new_right = horizontal_point;
+            }
+        }
+    }
   else
     {
       /* Disable edge resistance for resizes when windows have size
@@ -1223,7 +1267,6 @@ meta_window_edge_resistance_for_resize (MetaWindow  *window,
 {
   MetaRectangle old_outer, new_outer;
   int proposed_outer_width, proposed_outer_height;
-  gboolean is_resize;
 
   meta_window_get_frame_rect (window, &old_outer);
   proposed_outer_width  = *new_width;
@@ -1235,7 +1278,6 @@ meta_window_edge_resistance_for_resize (MetaWindow  *window,
                                       proposed_outer_height);
 
   window->display->grab_last_user_action_was_snap = snap;
-  is_resize = TRUE;
   if (apply_edge_resistance_to_each_side (window->display,
                                           window,
                                           &old_outer,
@@ -1243,7 +1285,7 @@ meta_window_edge_resistance_for_resize (MetaWindow  *window,
                                           timeout_func,
                                           snap,
                                           is_keyboard_op,
-                                          is_resize))
+                                          TRUE))
     {
       *new_width = new_outer.width;
       *new_height = new_outer.height;

src/core/keybindings.c

@@ -2221,12 +2221,14 @@ process_mouse_move_resize_grab (MetaDisplay     *display,
 
   if (event->keyval == CLUTTER_KEY_Escape)
     {
+      MetaTileMode tile_mode;
+
       /* Hide the tiling preview if necessary */
-      if (window->tile_mode != META_TILE_NONE)
+      if (screen->preview_tile_mode != META_TILE_NONE)
         meta_screen_hide_tile_preview (screen);
 
       /* Restore the original tile mode */
-      window->tile_mode = display->grab_tile_mode;
+      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
@@ -2234,10 +2236,13 @@ process_mouse_move_resize_grab (MetaDisplay     *display,
        * need to remaximize it.  In normal cases, we need to do a
        * moveresize now to get the position back to the original.
        */
-      if (window->shaken_loose || window->tile_mode == META_TILE_MAXIMIZED)
+      if (window->shaken_loose || tile_mode == META_TILE_MAXIMIZED)
         meta_window_maximize (window, META_MAXIMIZE_BOTH);
-      else if (window->tile_mode != META_TILE_NONE)
-        meta_window_tile (window);
+      else if (tile_mode != META_TILE_NONE)
+        meta_window_restore_tile (window,
+                                  tile_mode,
+                                  display->grab_initial_window_pos.width,
+                                  display->grab_initial_window_pos.height);
       else
         meta_window_move_resize_frame (display->grab_window,
                                        TRUE,
@@ -3184,7 +3189,6 @@ handle_toggle_tiled (MetaDisplay     *display,
   else if (meta_window_can_tile_side_by_side (window))
     {
       window->tile_monitor_number = window->monitor->number;
-      window->tile_mode = mode;
       /* Maximization constraints beat tiling constraints, so if the window
        * is maximized, tiling won't have any effect unless we unmaximize it
        * horizontally first; rather than calling meta_window_unmaximize(),
@@ -3192,7 +3196,7 @@ handle_toggle_tiled (MetaDisplay     *display,
        * save an additional roundtrip.
        */
       window->maximized_horizontally = FALSE;
-      meta_window_tile (window);
+      meta_window_tile (window, mode);
     }
 }
 

src/core/screen-private.h

@@ -56,6 +56,7 @@ struct _MetaScreen
   MetaUI *ui;
 
   guint tile_preview_timeout_id;
+  guint preview_tile_mode : 2;
 
   MetaWorkspace *active_workspace;
 

src/core/screen.c

@@ -308,6 +308,7 @@ set_supported_hint (MetaScreen *screen)
 
     screen->display->atom__GTK_FRAME_EXTENTS,
     screen->display->atom__GTK_SHOW_WINDOW_MENU,
+    screen->display->atom__GTK_EDGE_CONSTRAINTS,
   };
 
   XChangeProperty (screen->display->xdisplay, screen->xroot,
@@ -1410,7 +1411,7 @@ meta_screen_update_tile_preview_timeout (gpointer data)
 
   if (window)
     {
-      switch (window->tile_mode)
+      switch (screen->preview_tile_mode)
         {
           case META_TILE_LEFT:
           case META_TILE_RIGHT:
@@ -1435,7 +1436,7 @@ meta_screen_update_tile_preview_timeout (gpointer data)
       int monitor;
 
       monitor = meta_window_get_current_tile_monitor_number (window);
-      meta_window_get_current_tile_area (window, &tile_rect);
+      meta_window_get_tile_area (window, screen->preview_tile_mode, &tile_rect);
       meta_compositor_show_tile_preview (screen->display->compositor,
                                          window, &tile_rect, monitor);
     }
@@ -1479,6 +1480,7 @@ meta_screen_hide_tile_preview (MetaScreen *screen)
     g_source_remove (screen->tile_preview_timeout_id);
   screen->tile_preview_timeout_id = 0;
 
+  screen->preview_tile_mode = META_TILE_NONE;
   meta_compositor_hide_tile_preview (screen->display->compositor);
 }
 

src/core/window-private.h

@@ -129,6 +129,13 @@ typedef struct _MetaPlacementRule
   int height;
 } MetaPlacementRule;
 
+typedef enum
+{
+  META_EDGE_CONSTRAINT_NONE    = 0,
+  META_EDGE_CONSTRAINT_WINDOW  = 1,
+  META_EDGE_CONSTRAINT_MONITOR = 2,
+} MetaEdgeConstraint;
+
 struct _MetaWindow
 {
   GObject parent_instance;
@@ -199,14 +206,21 @@ struct _MetaWindow
   guint maximize_vertically_after_placement : 1;
   guint minimize_after_placement : 1;
 
-  /* The current or requested tile mode. If maximized_vertically is true,
-   * this is the current mode. If not, it is the mode which will be
-   * requested after the window grab is released */
+  /* The current tile mode */
   guint tile_mode : 2;
   /* The last "full" maximized/unmaximized state. We need to keep track of
    * that to toggle between normal/tiled or maximized/tiled states. */
   guint saved_maximize : 1;
   int tile_monitor_number;
+
+  /* 0 - top
+   * 1 - right
+   * 2 - bottom
+   * 3 - left */
+  MetaEdgeConstraint edge_constraints[4];
+
+  double tile_hfraction;
+
   int preferred_output_winsys_id;
 
   /* Whether we're shaded */
@@ -559,7 +573,7 @@ struct _MetaWindowClass
 #define META_WINDOW_TILED_MAXIMIZED(w)(META_WINDOW_MAXIMIZED(w) && \
                                        (w)->tile_mode == META_TILE_MAXIMIZED)
 #define META_WINDOW_ALLOWS_MOVE(w)     ((w)->has_move_func && !(w)->fullscreen)
-#define META_WINDOW_ALLOWS_RESIZE_EXCEPT_HINTS(w)   ((w)->has_resize_func && !META_WINDOW_MAXIMIZED (w) && !META_WINDOW_TILED_SIDE_BY_SIDE(w) && !(w)->fullscreen && !(w)->shaded)
+#define META_WINDOW_ALLOWS_RESIZE_EXCEPT_HINTS(w)   ((w)->has_resize_func && !META_WINDOW_MAXIMIZED (w) && !(w)->fullscreen && !(w)->shaded)
 #define META_WINDOW_ALLOWS_RESIZE(w)   (META_WINDOW_ALLOWS_RESIZE_EXCEPT_HINTS (w) &&                \
                                         (((w)->size_hints.min_width < (w)->size_hints.max_width) ||  \
                                          ((w)->size_hints.min_height < (w)->size_hints.max_height)))
@@ -579,7 +593,12 @@ void        meta_window_unmanage           (MetaWindow  *window,
                                             guint32      timestamp);
 void        meta_window_queue              (MetaWindow  *window,
                                             guint queuebits);
-void        meta_window_tile               (MetaWindow        *window);
+void        meta_window_tile               (MetaWindow        *window,
+                                            MetaTileMode       mode);
+void        meta_window_restore_tile       (MetaWindow        *window,
+                                            MetaTileMode       mode,
+                                            int                width,
+                                            int                height);
 void        meta_window_maximize_internal  (MetaWindow        *window,
                                             MetaMaximizeFlags  directions,
                                             MetaRectangle     *saved_rect);
@@ -648,8 +667,9 @@ void meta_window_get_work_area_for_logical_monitor (MetaWindow         *window,
                                                     MetaRectangle      *area);
 
 int meta_window_get_current_tile_monitor_number (MetaWindow *window);
-void meta_window_get_current_tile_area         (MetaWindow    *window,
-                                                MetaRectangle *tile_area);
+void meta_window_get_tile_area                  (MetaWindow    *window,
+                                                 MetaTileMode   mode,
+                                                 MetaRectangle *tile_area);
 
 
 gboolean meta_window_same_application (MetaWindow *window,

src/core/window.c

@@ -133,6 +133,10 @@ static void set_workspace_state (MetaWindow    *window,
                                  gboolean       on_all_workspaces,
                                  MetaWorkspace *workspace);
 
+static MetaWindow * meta_window_find_tile_match (MetaWindow   *window,
+                                                 MetaTileMode  mode);
+static void update_edge_constraints (MetaWindow *window);
+
 /* Idle handlers for the three queues (run with meta_later_add()). The
  * "data" parameter in each case will be a GINT_TO_POINTER of the
  * index into the queue arrays to use.
@@ -1017,6 +1021,7 @@ _meta_window_shared_new (MetaDisplay         *display,
   window->on_all_workspaces_requested = FALSE;
   window->tile_mode = META_TILE_NONE;
   window->tile_monitor_number = -1;
+  window->tile_hfraction = -1.;
   window->shaded = FALSE;
   window->initially_iconic = FALSE;
   window->minimized = FALSE;
@@ -2761,6 +2766,9 @@ meta_window_maximize_internal (MetaWindow        *window,
   window->maximized_vertically =
     window->maximized_vertically   || maximize_vertically;
 
+  /* Update the edge constraints */
+  update_edge_constraints (window);;
+
   meta_window_recalc_features (window);
   set_net_wm_state (window);
 
@@ -2968,12 +2976,122 @@ meta_window_requested_dont_bypass_compositor (MetaWindow *window)
   return window->bypass_compositor == _NET_WM_BYPASS_COMPOSITOR_HINT_OFF;
 }
 
+static void
+meta_window_get_tile_fraction (MetaWindow   *window,
+                               MetaTileMode  tile_mode,
+                               double       *fraction)
+{
+  MetaWindow *tile_match;
+
+  /* Make sure the tile match is up-to-date and matches the
+   * passed in mode rather than the current state
+   */
+  tile_match = meta_window_find_tile_match (window, tile_mode);
+
+  if (tile_mode == META_TILE_NONE)
+    *fraction = -1.;
+  else if (tile_mode == META_TILE_MAXIMIZED)
+    *fraction = 1.;
+  else if (tile_match)
+    *fraction = 1. - tile_match->tile_hfraction;
+  else if (META_WINDOW_TILED_SIDE_BY_SIDE (window))
+    {
+      if (window->tile_mode != tile_mode)
+        *fraction = 1. - window->tile_hfraction;
+      else
+        *fraction = window->tile_hfraction;
+    }
+  else
+    *fraction = .5;
+}
+
+static void
+meta_window_update_tile_fraction (MetaWindow *window,
+                                  int         new_w,
+                                  int         new_h)
+{
+  MetaWindow *tile_match = window->tile_match;
+  MetaRectangle work_area;
+
+  if (!META_WINDOW_TILED_SIDE_BY_SIDE (window))
+    return;
+
+  meta_window_get_work_area_for_monitor (window,
+                                         window->tile_monitor_number,
+                                         &work_area);
+  window->tile_hfraction = (double)new_w / work_area.width;
+
+  if (tile_match && window->display->grab_window == window)
+    meta_window_tile (tile_match, tile_match->tile_mode);
+}
+
+static void
+update_edge_constraints (MetaWindow *window)
+{
+  switch (window->tile_mode)
+    {
+    case META_TILE_NONE:
+      window->edge_constraints[0] = META_EDGE_CONSTRAINT_NONE;
+      window->edge_constraints[1] = META_EDGE_CONSTRAINT_NONE;
+      window->edge_constraints[2] = META_EDGE_CONSTRAINT_NONE;
+      window->edge_constraints[3] = META_EDGE_CONSTRAINT_NONE;
+      break;
+
+    case META_TILE_MAXIMIZED:
+      window->edge_constraints[0] = META_EDGE_CONSTRAINT_MONITOR;
+      window->edge_constraints[1] = META_EDGE_CONSTRAINT_MONITOR;
+      window->edge_constraints[2] = META_EDGE_CONSTRAINT_MONITOR;
+      window->edge_constraints[3] = META_EDGE_CONSTRAINT_MONITOR;
+      break;
+
+    case META_TILE_LEFT:
+      window->edge_constraints[0] = META_EDGE_CONSTRAINT_MONITOR;
+
+      if (window->tile_match)
+        window->edge_constraints[1] = META_EDGE_CONSTRAINT_WINDOW;
+      else
+        window->edge_constraints[1] = META_EDGE_CONSTRAINT_NONE;
+
+      window->edge_constraints[2] = META_EDGE_CONSTRAINT_MONITOR;
+      window->edge_constraints[3] = META_EDGE_CONSTRAINT_MONITOR;
+      break;
+
+    case META_TILE_RIGHT:
+      window->edge_constraints[0] = META_EDGE_CONSTRAINT_MONITOR;
+      window->edge_constraints[1] = META_EDGE_CONSTRAINT_MONITOR;
+      window->edge_constraints[2] = META_EDGE_CONSTRAINT_MONITOR;
+
+      if (window->tile_match)
+        window->edge_constraints[3] = META_EDGE_CONSTRAINT_WINDOW;
+      else
+        window->edge_constraints[3] = META_EDGE_CONSTRAINT_NONE;
+      break;
+    }
+
+  /* h/vmaximize also modify the edge constraints */
+  if (window->maximized_vertically)
+    {
+      window->edge_constraints[0] = META_EDGE_CONSTRAINT_MONITOR;
+      window->edge_constraints[2] = META_EDGE_CONSTRAINT_MONITOR;
+    }
+
+  if (window->maximized_horizontally)
+    {
+      window->edge_constraints[1] = META_EDGE_CONSTRAINT_MONITOR;
+      window->edge_constraints[3] = META_EDGE_CONSTRAINT_MONITOR;
+    }
+}
+
 void
-meta_window_tile (MetaWindow *window)
+meta_window_tile (MetaWindow   *window,
+                  MetaTileMode  tile_mode)
 {
   MetaMaximizeFlags directions;
   MetaRectangle old_frame_rect, old_buffer_rect;
 
+  meta_window_get_tile_fraction (window, tile_mode, &window->tile_hfraction);
+  window->tile_mode = tile_mode;
+
   /* Don't do anything if no tiling is requested */
   if (window->tile_mode == META_TILE_NONE)
     return;
@@ -2986,6 +3104,9 @@ meta_window_tile (MetaWindow *window)
   meta_window_maximize_internal (window, directions, NULL);
   meta_screen_update_tile_preview (window->screen, FALSE);
 
+  /* Setup the edge constraints */
+  update_edge_constraints (window);
+
   meta_window_get_frame_rect (window, &old_frame_rect);
   meta_window_get_buffer_rect (window, &old_buffer_rect);
 
@@ -3004,6 +3125,16 @@ meta_window_tile (MetaWindow *window)
     meta_frame_queue_draw (window->frame);
 }
 
+void
+meta_window_restore_tile (MetaWindow   *window,
+                          MetaTileMode  mode,
+                          int           width,
+                          int           height)
+{
+  meta_window_update_tile_fraction (window, width, height);
+  meta_window_tile (window, mode);
+}
+
 static gboolean
 meta_window_can_tile_maximized (MetaWindow *window)
 {
@@ -3102,6 +3233,9 @@ meta_window_unmaximize (MetaWindow        *window,
       meta_window_get_frame_rect (window, &old_frame_rect);
       meta_window_get_buffer_rect (window, &old_buffer_rect);
 
+      if (unmaximize_vertically)
+        window->tile_mode = META_TILE_NONE;
+
       meta_topic (META_DEBUG_WINDOW_OPS,
                   "Unmaximizing %s%s\n",
                   window->desc,
@@ -3114,6 +3248,9 @@ meta_window_unmaximize (MetaWindow        *window,
       window->maximized_vertically =
         window->maximized_vertically   && !unmaximize_vertically;
 
+      /* Update the edge constraints */
+      update_edge_constraints (window);
+
       /* recalc_features() will eventually clear the cached frame
        * extents, but we need the correct frame extents in the code below,
        * so invalidate the old frame extents manually up front.
@@ -3977,6 +4114,9 @@ meta_window_move_to_monitor (MetaWindow  *window,
 {
   MetaRectangle old_area, new_area;
 
+  if (window->tile_mode != META_TILE_NONE)
+    window->tile_monitor_number = monitor;
+
   meta_window_get_work_area_for_monitor (window,
                                          window->monitor->number,
                                          &old_area);
@@ -3998,15 +4138,40 @@ meta_window_move_to_monitor (MetaWindow  *window,
       meta_window_move_between_rects (window, &old_area, &new_area);
     }
 
-  if (window->tile_mode != META_TILE_NONE)
-    window->tile_monitor_number = monitor;
-
   window->preferred_output_winsys_id = window->monitor->winsys_id;
 
   if (window->fullscreen || window->override_redirect)
     meta_screen_queue_check_fullscreen (window->screen);
 }
 
+static void
+adjust_size_for_tile_match (MetaWindow *window,
+                            int        *new_w,
+                            int        *new_h)
+{
+  MetaRectangle work_area, rect;
+  MetaWindow *tile_match = window->tile_match;
+
+  if (!META_WINDOW_TILED_SIDE_BY_SIDE (window) || !tile_match)
+    return;
+
+  meta_window_get_work_area_for_monitor (window, window->tile_monitor_number, &work_area);
+
+  /* Make sure the resize does not break minimum sizes */
+  rect = work_area;
+  rect.width = *new_w;
+
+  meta_window_frame_rect_to_client_rect (window, &rect, &rect);
+  *new_w += MAX(0, window->size_hints.min_width - rect.width);
+
+  /* Make sure we're not resizing the tile match below its min width */
+  rect = work_area;
+  rect.width = work_area.width - *new_w;
+
+  meta_window_frame_rect_to_client_rect (tile_match, &rect, &rect);
+  *new_w -= MAX(0, tile_match->size_hints.min_width - rect.width);
+}
+
 void
 meta_window_resize_frame_with_gravity (MetaWindow *window,
                                        gboolean     user_op,
@@ -4020,6 +4185,16 @@ meta_window_resize_frame_with_gravity (MetaWindow *window,
   rect.width = w;
   rect.height = h;
 
+  if (user_op)
+    {
+      /* When resizing in-tandem with a tile match, we need to respect
+       * its minimum width
+       */
+      if (window->display->grab_window == window)
+        adjust_size_for_tile_match (window, &w, &h);
+      meta_window_update_tile_fraction (window, w, h);
+    }
+
   flags = (user_op ? META_MOVE_RESIZE_USER_ACTION : 0) | META_MOVE_RESIZE_RESIZE_ACTION;
   meta_window_move_resize_internal (window, flags, gravity, rect);
 }
@@ -4764,7 +4939,13 @@ meta_window_raise (MetaWindow  *window)
    * the child windows appropriately.
    */
   if (window->screen->stack == ancestor->screen->stack)
-    meta_stack_raise (window->screen->stack, ancestor);
+    {
+      /* If the window has a tile sibling, raise it before raising the window itself */
+      if (window->tile_match)
+        meta_stack_raise (window->tile_match->screen->stack, window->tile_match);
+
+      meta_stack_raise (window->screen->stack, ancestor);
+    }
   else
     {
       meta_warning (
@@ -4796,6 +4977,10 @@ meta_window_lower (MetaWindow  *window)
   meta_topic (META_DEBUG_WINDOW_OPS,
               "Lowering window %s\n", window->desc);
 
+  /* If the window has a tile sibling, lower it before loweting the window itself */
+  if (window->tile_match)
+    meta_stack_lower (window->tile_match->screen->stack, window->tile_match);
+
   meta_stack_lower (window->screen->stack, window);
 }
 
@@ -5713,6 +5898,7 @@ update_move_maybe_tile (MetaWindow *window,
   MetaMonitorManager *monitor_manager =
     meta_backend_get_monitor_manager (backend);
   MetaLogicalMonitor *logical_monitor;
+  MetaScreen *screen = window->screen;
   MetaRectangle work_area;
 
   /* For side-by-side tiling we are interested in the inside vertical
@@ -5742,18 +5928,18 @@ update_move_maybe_tile (MetaWindow *window,
    */
   if (meta_window_can_tile_side_by_side (window) &&
       x >= logical_monitor->rect.x && x < (work_area.x + shake_threshold))
-    window->tile_mode = META_TILE_LEFT;
+    screen->preview_tile_mode = META_TILE_LEFT;
   else if (meta_window_can_tile_side_by_side (window) &&
            x >= work_area.x + work_area.width - shake_threshold &&
            x < (logical_monitor->rect.x + logical_monitor->rect.width))
-    window->tile_mode = META_TILE_RIGHT;
+    screen->preview_tile_mode = META_TILE_RIGHT;
   else if (meta_window_can_tile_maximized (window) &&
            y >= logical_monitor->rect.y && y <= work_area.y)
-    window->tile_mode = META_TILE_MAXIMIZED;
+    screen->preview_tile_mode = META_TILE_MAXIMIZED;
   else
-    window->tile_mode = META_TILE_NONE;
+    screen->preview_tile_mode = META_TILE_NONE;
 
-  if (window->tile_mode != META_TILE_NONE)
+  if (screen->preview_tile_mode != META_TILE_NONE)
     window->tile_monitor_number = logical_monitor->number;
 }
 
@@ -5768,6 +5954,7 @@ update_move (MetaWindow  *window,
   MetaRectangle old;
   int shake_threshold;
   MetaDisplay *display = window->display;
+  MetaScreen *screen = window->screen;
 
   display->grab_latest_motion_x = x;
   display->grab_latest_motion_y = y;
@@ -5805,7 +5992,7 @@ update_move (MetaWindow  *window,
     {
       /* We don't want to tile while snapping. Also, clear any previous tile
          request. */
-      window->tile_mode = META_TILE_NONE;
+      screen->preview_tile_mode = META_TILE_NONE;
       window->tile_monitor_number = -1;
     }
   else if (meta_prefs_get_edge_tiling () &&
@@ -5921,8 +6108,8 @@ update_move (MetaWindow  *window,
    * trigger it unwittingly, e.g. when shaking loose the window or moving
    * it to another monitor.
    */
-  meta_screen_update_tile_preview (window->screen,
-                                   window->tile_mode != META_TILE_NONE);
+  meta_screen_update_tile_preview (screen,
+                                   screen->preview_tile_mode != META_TILE_NONE);
 
   meta_window_get_frame_rect (window, &old);
 
@@ -6089,20 +6276,21 @@ update_resize (MetaWindow *window,
 }
 
 static void
-update_tile_mode (MetaWindow *window)
+maybe_maximize_tiled_window (MetaWindow *window)
 {
-  switch (window->tile_mode)
-    {
-      case META_TILE_LEFT:
-      case META_TILE_RIGHT:
-          if (!META_WINDOW_TILED_SIDE_BY_SIDE (window))
-              window->tile_mode = META_TILE_NONE;
-          break;
-      case META_TILE_MAXIMIZED:
-          if (!META_WINDOW_MAXIMIZED (window))
-              window->tile_mode = META_TILE_NONE;
-          break;
-    }
+  MetaRectangle work_area;
+  gint shake_threshold;
+
+  if (!META_WINDOW_TILED_SIDE_BY_SIDE (window))
+    return;
+
+  shake_threshold = meta_prefs_get_drag_threshold ();
+
+  meta_window_get_work_area_for_monitor (window,
+                                         window->tile_monitor_number,
+                                         &work_area);
+  if (window->rect.width >= work_area.width - shake_threshold)
+    meta_window_maximize (window, META_MAXIMIZE_BOTH);
 }
 
 void
@@ -6135,8 +6323,8 @@ end_grab_op (MetaWindow *window,
     {
       if (meta_grab_op_is_moving (window->display->grab_op))
         {
-          if (window->tile_mode != META_TILE_NONE)
-            meta_window_tile (window);
+          if (window->screen->preview_tile_mode != META_TILE_NONE)
+            meta_window_tile (window, window->screen->preview_tile_mode);
           else
             update_move (window,
                          modifiers & CLUTTER_SHIFT_MASK,
@@ -6145,20 +6333,13 @@ end_grab_op (MetaWindow *window,
       else if (meta_grab_op_is_resizing (window->display->grab_op))
         {
           update_resize (window,
-                         modifiers & CLUTTER_SHIFT_MASK,
+                         modifiers & CLUTTER_SHIFT_MASK || window->tile_match != NULL,
                          x, y,
                          TRUE);
-
-          /* If a tiled window has been dragged free with a
-           * mouse resize without snapping back to the tiled
-           * state, it will end up with an inconsistent tile
-           * mode on mouse release; cleaning the mode earlier
-           * would break the ability to snap back to the tiled
-           * state, so we wait until mouse release.
-           */
-          update_tile_mode (window);
+          maybe_maximize_tiled_window (window);
         }
     }
+  window->screen->preview_tile_mode = META_TILE_NONE;
   meta_display_end_grab_op (window->display, clutter_event_get_time (event));
 }
 
@@ -6229,7 +6410,7 @@ meta_window_handle_mouse_grab_op_event  (MetaWindow         *window,
       else if (meta_grab_op_is_resizing (window->display->grab_op))
         {
           update_resize (window,
-                         modifier_state & CLUTTER_SHIFT_MASK,
+                         modifier_state & CLUTTER_SHIFT_MASK || window->tile_match != NULL,
                          x, y,
                          FALSE);
         }
@@ -6362,23 +6543,26 @@ meta_window_get_current_tile_monitor_number (MetaWindow *window)
 }
 
 void
-meta_window_get_current_tile_area (MetaWindow    *window,
-                                   MetaRectangle *tile_area)
+meta_window_get_tile_area (MetaWindow    *window,
+                           MetaTileMode   tile_mode,
+                           MetaRectangle *tile_area)
 {
+  MetaRectangle work_area;
   int tile_monitor_number;
+  double fraction;
 
-  g_return_if_fail (window->tile_mode != META_TILE_NONE);
+  g_return_if_fail (tile_mode != META_TILE_NONE);
 
   tile_monitor_number = meta_window_get_current_tile_monitor_number (window);
 
-  meta_window_get_work_area_for_monitor (window, tile_monitor_number, tile_area);
+  meta_window_get_work_area_for_monitor (window, tile_monitor_number, &work_area);
+  meta_window_get_tile_fraction (window, tile_mode, &fraction);
 
-  if (window->tile_mode == META_TILE_LEFT  ||
-      window->tile_mode == META_TILE_RIGHT)
-    tile_area->width /= 2;
+  *tile_area = work_area;
+  tile_area->width = round (tile_area->width * fraction);
 
-  if (window->tile_mode == META_TILE_RIGHT)
-    tile_area->x += tile_area->width;
+  if (tile_mode == META_TILE_RIGHT)
+    tile_area->x += work_area.width - tile_area->width;
 }
 
 gboolean
@@ -7511,22 +7695,27 @@ meta_window_get_tile_match (MetaWindow *window)
 
 void
 meta_window_compute_tile_match (MetaWindow *window)
+{
+  window->tile_match = meta_window_find_tile_match (window, window->tile_mode);
+}
+
+static MetaWindow *
+meta_window_find_tile_match (MetaWindow   *window,
+                             MetaTileMode  current_mode)
 {
   MetaWindow *match;
   MetaStack *stack;
   MetaTileMode match_tile_mode = META_TILE_NONE;
 
-  window->tile_match = NULL;
-
   if (window->shaded || window->minimized)
-    return;
+    return NULL;
 
-  if (META_WINDOW_TILED_LEFT (window))
+  if (current_mode == META_TILE_LEFT)
     match_tile_mode = META_TILE_RIGHT;
-  else if (META_WINDOW_TILED_RIGHT (window))
+  else if (current_mode == META_TILE_RIGHT)
     match_tile_mode = META_TILE_LEFT;
   else
-    return;
+    return NULL;
 
   stack = window->screen->stack;
 
@@ -7537,7 +7726,7 @@ meta_window_compute_tile_match (MetaWindow *window)
       if (!match->shaded &&
           !match->minimized &&
           match->tile_mode == match_tile_mode &&
-          match->monitor == window->monitor &&
+          match->tile_monitor_number == window->tile_monitor_number &&
           meta_window_get_workspace (match) == meta_window_get_workspace (window))
         break;
     }
@@ -7560,6 +7749,23 @@ meta_window_compute_tile_match (MetaWindow *window)
 
       meta_window_get_frame_rect (bottommost, &bottommost_rect);
       meta_window_get_frame_rect (topmost, &topmost_rect);
+
+      /*
+       * If we are looking for a tile match while actually being tiled,
+       * rather than a match for a potential tile mode, then discard
+       * windows with too much gap or overlap
+       */
+      if (window->tile_mode == current_mode &&
+          !(meta_grab_op_is_resizing (window->display->grab_op) &&
+            window->display->grab_window == window &&
+            window->tile_match != NULL))
+        {
+          int threshold = meta_prefs_get_drag_threshold ();
+          if (ABS (topmost_rect.x - bottommost_rect.x - bottommost_rect.width) > threshold &&
+              ABS (bottommost_rect.x - topmost_rect.x - topmost_rect.width) > threshold)
+            return NULL;
+        }
+
       /*
        * If there's a window stacked in between which is partially visible
        * behind the topmost tile we don't consider the tiles to match.
@@ -7577,11 +7783,11 @@ meta_window_compute_tile_match (MetaWindow *window)
 
           if (meta_rectangle_overlap (&above_rect, &bottommost_rect) &&
               meta_rectangle_overlap (&above_rect, &topmost_rect))
-            return;
+            return NULL;
         }
-
-      window->tile_match = match;
     }
+
+  return match;
 }
 
 void

src/ui/frames.c

@@ -1621,6 +1621,9 @@ get_control (MetaUIFrame *frame, int root_x, int root_y)
   has_vert = (flags & META_FRAME_ALLOWS_VERTICAL_RESIZE) != 0;
   has_horiz = (flags & META_FRAME_ALLOWS_HORIZONTAL_RESIZE) != 0;
 
+  if (flags & META_FRAME_TILED_LEFT || flags & META_FRAME_TILED_RIGHT)
+    has_vert = has_horiz = FALSE;
+
   if (POINT_IN_RECT (x, y, fgeom.title_rect))
     {
       if (has_vert && y <= TOP_RESIZE_HEIGHT && has_north_resize)
@@ -1693,12 +1696,12 @@ get_control (MetaUIFrame *frame, int root_x, int root_y)
     }
   else if (x <= fgeom.borders.total.left)
     {
-      if (has_horiz)
+      if (has_horiz || flags & META_FRAME_TILED_RIGHT)
         return META_FRAME_CONTROL_RESIZE_W;
     }
   else if (x >= (fgeom.width - fgeom.borders.total.right))
     {
-      if (has_horiz)
+      if (has_horiz || flags & META_FRAME_TILED_LEFT)
         return META_FRAME_CONTROL_RESIZE_E;
     }
 

src/wayland/meta-wayland-gtk-shell.c

@@ -148,31 +148,124 @@ gtk_surface_surface_destroyed (MetaWaylandGtkSurface *gtk_surface)
 }
 
 static void
-fill_states (struct wl_array *states,
-             MetaWindow      *window)
+fill_edge_states (struct wl_array *states,
+                  MetaWindow      *window)
 {
   uint32_t *s;
 
-  if (window->tile_mode == META_TILE_LEFT ||
-      window->tile_mode == META_TILE_RIGHT)
+  /* Top */
+  if (window->edge_constraints[0] != META_EDGE_CONSTRAINT_MONITOR)
+    {
+      s = wl_array_add (states, sizeof *s);
+      *s = GTK_SURFACE1_EDGE_CONSTRAINT_RESIZABLE_TOP;
+    }
+
+  /* Right */
+  if (window->edge_constraints[1] != META_EDGE_CONSTRAINT_MONITOR)
+    {
+      s = wl_array_add (states, sizeof *s);
+      *s = GTK_SURFACE1_EDGE_CONSTRAINT_RESIZABLE_RIGHT;
+    }
+
+  /* Bottom */
+  if (window->edge_constraints[2] != META_EDGE_CONSTRAINT_MONITOR)
+    {
+      s = wl_array_add (states, sizeof *s);
+      *s = GTK_SURFACE1_EDGE_CONSTRAINT_RESIZABLE_BOTTOM;
+    }
+
+  /* Left */
+  if (window->edge_constraints[3] != META_EDGE_CONSTRAINT_MONITOR)
+    {
+      s = wl_array_add (states, sizeof *s);
+      *s = GTK_SURFACE1_EDGE_CONSTRAINT_RESIZABLE_LEFT;
+    }
+}
+
+static void
+send_configure_edges (MetaWaylandGtkSurface *gtk_surface,
+                      MetaWindow            *window)
+{
+  struct wl_array edge_states;
+
+  wl_array_init (&edge_states);
+  fill_edge_states (&edge_states, window);
+
+  gtk_surface1_send_configure_edges (gtk_surface->resource, &edge_states);
+
+  wl_array_release (&edge_states);
+}
+
+static void
+fill_states (struct wl_array    *states,
+             MetaWindow         *window,
+             struct wl_resource *resource)
+{
+  uint32_t *s;
+  guint version;
+
+  version = wl_resource_get_version (resource);
+
+  if (version < GTK_SURFACE1_CONFIGURE_EDGES_SINCE_VERSION &&
+      (window->tile_mode == META_TILE_LEFT ||
+       window->tile_mode == META_TILE_RIGHT))
     {
       s = wl_array_add (states, sizeof *s);
       *s = GTK_SURFACE1_STATE_TILED;
     }
+
+  if (version >= GTK_SURFACE1_STATE_TILED_TOP_SINCE_VERSION &&
+      window->edge_constraints[0] != META_EDGE_CONSTRAINT_NONE)
+    {
+      s = wl_array_add (states, sizeof *s);
+      *s = GTK_SURFACE1_STATE_TILED_TOP;
+    }
+
+  if (version >= GTK_SURFACE1_STATE_TILED_RIGHT_SINCE_VERSION &&
+      window->edge_constraints[1] != META_EDGE_CONSTRAINT_NONE)
+    {
+      s = wl_array_add (states, sizeof *s);
+      *s = GTK_SURFACE1_STATE_TILED_RIGHT;
+    }
+
+  if (version >= GTK_SURFACE1_STATE_TILED_BOTTOM_SINCE_VERSION &&
+      window->edge_constraints[2] != META_EDGE_CONSTRAINT_NONE)
+    {
+      s = wl_array_add (states, sizeof *s);
+      *s = GTK_SURFACE1_STATE_TILED_BOTTOM;
+    }
+
+  if (version >= GTK_SURFACE1_STATE_TILED_LEFT_SINCE_VERSION &&
+      window->edge_constraints[3] != META_EDGE_CONSTRAINT_NONE)
+    {
+      s = wl_array_add (states, sizeof *s);
+      *s = GTK_SURFACE1_STATE_TILED_LEFT;
+    }
+}
+
+static void
+send_configure (MetaWaylandGtkSurface *gtk_surface,
+                MetaWindow            *window)
+{
+  struct wl_array states;
+
+  wl_array_init (&states);
+  fill_states (&states, window, gtk_surface->resource);
+
+  gtk_surface1_send_configure (gtk_surface->resource, &states);
+
+  wl_array_release (&states);
 }
 
 static void
 on_configure (MetaWaylandSurface    *surface,
               MetaWaylandGtkSurface *gtk_surface)
 {
-  struct wl_array states;
+  send_configure (gtk_surface, surface->window);
 
-  wl_array_init (&states);
-  fill_states (&states, surface->window);
 
-  gtk_surface1_send_configure (gtk_surface->resource, &states);
-
-  wl_array_release (&states);
+  if (wl_resource_get_version (gtk_surface->resource) >= GTK_SURFACE1_CONFIGURE_EDGES_SINCE_VERSION)
+    send_configure_edges (gtk_surface, surface->window);
 }
 
 static void

src/wayland/meta-wayland-versions.h

@@ -42,7 +42,7 @@
 #define META_WL_SEAT_VERSION                5
 #define META_WL_OUTPUT_VERSION              2
 #define META_XSERVER_VERSION                1
-#define META_GTK_SHELL1_VERSION             1
+#define META_GTK_SHELL1_VERSION             2
 #define META_WL_SUBCOMPOSITOR_VERSION       1
 #define META_ZWP_POINTER_GESTURES_V1_VERSION    1
 #define META_ZXDG_EXPORTER_V1_VERSION       1

src/wayland/protocol/gtk-shell.xml

@@ -1,6 +1,6 @@
 <protocol name="gtk">
 
-  <interface name="gtk_shell1" version="1">
+  <interface name="gtk_shell1" version="2">
     <description summary="gtk specific extensions">
       gtk_shell is a protocol extension providing additional features for
       clients implementing it.
@@ -30,7 +30,7 @@
     </request>
   </interface>
 
-  <interface name="gtk_surface1" version="1">
+  <interface name="gtk_surface1" version="2">
     <request name="set_dbus_properties">
       <arg name="application_id" type="string" allow-null="true"/>
       <arg name="app_menu_path" type="string" allow-null="true"/>
@@ -51,11 +51,27 @@
 
     <enum name="state">
       <entry name="tiled" value="1"/>
+
+      <entry name="tiled_top" value="2" since="2" />
+      <entry name="tiled_right" value="3" since="2" />
+      <entry name="tiled_bottom" value="4" since="2" />
+      <entry name="tiled_left" value="5"  since="2" />
+    </enum>
+
+    <enum name="edge_constraint" since="2">
+      <entry name="resizable_top" value="1"/>
+      <entry name="resizable_right" value="2"/>
+      <entry name="resizable_bottom" value="3"/>
+      <entry name="resizable_left" value="4"/>
     </enum>
 
     <event name="configure">
       <arg name="states" type="array"/>
     </event>
+
+    <event name="configure_edges" since="2">
+      <arg name="constraints" type="array"/>
+    </event>
   </interface>
 
 </protocol>

src/x11/atomnames.h

@@ -63,6 +63,7 @@ item(_GTK_APP_MENU_OBJECT_PATH)
 item(_GTK_MENUBAR_OBJECT_PATH)
 item(_GTK_FRAME_EXTENTS)
 item(_GTK_SHOW_WINDOW_MENU)
+item(_GTK_EDGE_CONSTRAINTS)
 item(_GNOME_WM_KEYBINDINGS)
 item(_GNOME_PANEL_ACTION)
 item(_GNOME_PANEL_ACTION_MAIN_MENU)

src/x11/window-x11.c

@@ -902,6 +902,31 @@ update_net_frame_extents (MetaWindow *window)
   meta_error_trap_pop (window->display);
 }
 
+static void
+update_gtk_edge_constraints (MetaWindow *window)
+{
+  MetaEdgeConstraint *constraints = window->edge_constraints;
+  unsigned long data[1];
+
+  /* Edge constraints */
+  data[0] = (constraints[0] != META_EDGE_CONSTRAINT_NONE ? 1 : 0)    << 0 |
+            (constraints[0] != META_EDGE_CONSTRAINT_MONITOR ? 1 : 0) << 1 |
+            (constraints[1] != META_EDGE_CONSTRAINT_NONE ? 1 : 0)    << 2 |
+            (constraints[1] != META_EDGE_CONSTRAINT_MONITOR ? 1 : 0) << 3 |
+            (constraints[2] != META_EDGE_CONSTRAINT_NONE ? 1 : 0)    << 4 |
+            (constraints[2] != META_EDGE_CONSTRAINT_MONITOR ? 1 : 0) << 5 |
+            (constraints[3] != META_EDGE_CONSTRAINT_NONE ? 1 : 0)    << 6 |
+            (constraints[3] != META_EDGE_CONSTRAINT_MONITOR ? 1 : 0) << 7;
+
+  meta_verbose ("Setting _GTK_EDGE_CONSTRAINTS to %lu\n", data[0]);
+
+  XChangeProperty (window->display->xdisplay,
+                   window->xwindow,
+                   window->display->atom__GTK_EDGE_CONSTRAINTS,
+                   XA_CARDINAL, 32, PropModeReplace,
+                   (guchar*) data, 1);
+}
+
 static gboolean
 sync_request_timeout (gpointer data)
 {
@@ -1259,6 +1284,8 @@ meta_window_x11_move_resize_internal (MetaWindow                *window,
     *result |= META_MOVE_RESIZE_RESULT_MOVED;
   if (need_resize_client || need_resize_frame)
     *result |= META_MOVE_RESIZE_RESULT_RESIZED;
+
+  update_gtk_edge_constraints (window);
 }
 
 static gboolean
@@ -1670,6 +1697,9 @@ meta_window_x11_set_net_wm_state (MetaWindow *window)
           meta_error_trap_pop (window->display);
         }
     }
+
+  /* Edge constraints */
+  update_gtk_edge_constraints (window);
 }
 
 static cairo_region_t *