wayland/xdg-toplevel-drag: Plumb xdg-toplevel-drag to core/compositor

- Event stream adaptations. When there is a toplevel-drag in place, do:
  - Send wl_data_source.dnd_finished and end the session successfully
  - Send wl_data_source.cancelled and end the MetaWindowDrag when ESC key
    is pressed.
- Modify MetaWaylandDataDevice such that, when a toplevel-drag is
  running, it does:
  - Propagate motion events, so that they can be processed further by
    MetaWindowDrag.
  - Ends the associated MetaWindowDrag upon release event.
- Hook up the window mapping process in MetaWindowWayand, such that:
  - the initial position of the window attached to the ongoing
    toplevel-drag instance can be calculated and set.
  - the appropriate gravity and flags can be set when calling MetaWindow's
    meta_window_move_resize_internal, which allows it for example to be
    moved freely (unconstrained) as per current dragging cursor.

Status:

- [x] Basic window drag triggering
- [x] Exclude the dragged window from event targets
- [x] Event forwarding (window drag vs wayland grabs)
- [x] Offset calc relative to toplevel geometry
- [x] Attach already mapped windows
- [x] Properly support not-yet-mapped windows
- [x] Disable visibility change animations
- [x] Dnd events stream adaptations

Signed-off-by: Nick Diego Yamane <nickdiego@igalia.com>
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4107>

src/wayland/meta-wayland-data-device.c

@@ -36,14 +36,20 @@
 
 #include "backends/meta-dnd-private.h"
 #include "compositor/meta-dnd-actor-private.h"
+#include "compositor/meta-surface-actor.h"
+#include "compositor/meta-window-drag.h"
 #include "core/meta-selection-private.h"
+#include "meta/meta-debug.h"
 #include "meta/meta-selection-source-memory.h"
+#include "meta/meta-wayland-surface.h"
 #include "wayland/meta-selection-source-wayland-private.h"
+#include "wayland/meta-wayland-data-source.h"
 #include "wayland/meta-wayland-dnd-surface.h"
 #include "wayland/meta-wayland-pointer.h"
 #include "wayland/meta-wayland-private.h"
 #include "wayland/meta-wayland-seat.h"
 #include "wayland/meta-wayland-toplevel-drag.h"
+#include "wayland/meta-wayland-types.h"
 
 #define ROOTWINDOW_DROP_MIME "application/x-rootwindow-drop"
 
@@ -510,6 +516,12 @@ data_device_update_position (MetaWaylandDragGrab *drag_grab,
   meta_wayland_surface_set_main_monitor (drag_grab->drag_surface, monitor);
 }
 
+static gboolean
+is_dragging_window (MetaWaylandSeat *seat)
+{
+  return meta_wayland_data_device_get_toplevel_drag (&seat->data_device) != NULL;
+}
+
 static gboolean
 drag_grab_motion (MetaWaylandEventHandler *handler,
 		  const ClutterEvent      *event,
@@ -540,7 +552,7 @@ drag_grab_motion (MetaWaylandEventHandler *handler,
 
   meta_dnd_wayland_on_motion_event (meta_backend_get_dnd (backend), event);
 
-  return CLUTTER_EVENT_STOP;
+  return !is_dragging_window (drag_grab->seat);
 }
 
 static gboolean
@@ -551,6 +563,7 @@ drag_grab_release (MetaWaylandEventHandler *handler,
   MetaWaylandDragGrab *drag_grab = user_data;
   MetaWaylandSeat *seat = drag_grab->seat;
   MetaWaylandDataSource *source = drag_grab->drag_data_source;
+  MetaWaylandToplevelDrag *toplevel_drag;
   gboolean success;
 
   if (drag_grab->device != clutter_event_get_device (event) ||
@@ -565,12 +578,22 @@ drag_grab_release (MetaWaylandEventHandler *handler,
                            CLUTTER_BUTTON5_MASK)) > 1)
     return CLUTTER_EVENT_STOP;
 
+  toplevel_drag = meta_wayland_data_device_get_toplevel_drag (&seat->data_device);
+  if (toplevel_drag)
+    {
+      meta_topic (META_DEBUG_WAYLAND, "Will end xdg_toplevel_drag#%u.",
+                  wl_resource_get_id (toplevel_drag->resource));
+      meta_wayland_data_source_notify_drop_performed (source);
+      meta_wayland_toplevel_drag_end (toplevel_drag);
+    }
+
   if (drag_grab->drag_focus && source &&
       meta_wayland_data_source_has_target (source) &&
       meta_wayland_data_source_get_current_action (source))
     {
       meta_wayland_surface_drag_dest_drop (drag_grab->drag_focus);
-      meta_wayland_data_source_notify_drop_performed (source);
+      if (!meta_wayland_data_source_get_drop_performed (source))
+        meta_wayland_data_source_notify_drop_performed (source);
 
       meta_wayland_data_source_update_in_ask (source);
       success = TRUE;
@@ -609,11 +632,20 @@ drag_grab_key (MetaWaylandEventHandler *handler,
                const ClutterEvent      *event,
                gpointer                 user_data)
 {
+  MetaWaylandToplevelDrag *toplevel_drag;
   MetaWaylandDragGrab *drag_grab = user_data;
   ClutterModifierType modifiers;
 
   if (clutter_event_get_key_symbol (event) == CLUTTER_KEY_Escape)
     {
+      toplevel_drag = meta_wayland_data_device_get_toplevel_drag (&drag_grab->seat->data_device);
+      if (toplevel_drag)
+        {
+          meta_topic (META_DEBUG_WAYLAND, "Will cancel xdg_toplevel_drag#%u.",
+                      wl_resource_get_id (toplevel_drag->resource));
+          meta_wayland_toplevel_drag_end (toplevel_drag);
+        }
+
       meta_wayland_data_device_set_dnd_source (&drag_grab->seat->data_device,
                                                NULL);
       unset_selection_source (&drag_grab->seat->data_device, META_SELECTION_DND);
@@ -1309,3 +1341,12 @@ meta_wayland_data_device_unset_dnd_selection (MetaWaylandDataDevice *data_device
 {
   unset_selection_source (data_device, META_SELECTION_DND);
 }
+
+MetaWaylandToplevelDrag *
+meta_wayland_data_device_get_toplevel_drag (MetaWaylandDataDevice *data_device)
+{
+  if (!data_device->current_grab || !data_device->current_grab->drag_data_source)
+    return NULL;
+
+  return meta_wayland_data_source_get_toplevel_drag (data_device->current_grab->drag_data_source);
+}

src/wayland/meta-wayland-data-device.h

@@ -87,6 +87,9 @@ void meta_wayland_data_device_start_drag (MetaWaylandDataDevice           *data_
 
 void     meta_wayland_data_device_end_drag       (MetaWaylandDataDevice                 *data_device);
 
+MetaWaylandToplevelDrag *
+meta_wayland_data_device_get_toplevel_drag (MetaWaylandDataDevice *data_device);
+
 void     meta_wayland_drag_grab_set_focus        (MetaWaylandDragGrab             *drag_grab,
                                                   MetaWaylandSurface              *surface);
 MetaWaylandSurface *

src/wayland/meta-window-wayland.c

@@ -39,6 +39,7 @@
 #include "wayland/meta-wayland-actor-surface.h"
 #include "wayland/meta-wayland-private.h"
 #include "wayland/meta-wayland-surface-private.h"
+#include "wayland/meta-wayland-toplevel-drag.h"
 #include "wayland/meta-wayland-window-configuration.h"
 #include "wayland/meta-wayland-xdg-shell.h"
 
@@ -732,6 +733,21 @@ on_window_shown (MetaWindow *window)
     meta_compositor_sync_updates_frozen (window->display->compositor, window);
 }
 
+static MetaWaylandToplevelDrag *
+get_toplevel_drag (MetaWindow *window)
+{
+  MetaWaylandToplevelDrag *toplevel_drag;
+  MetaWindowWayland *wl_window = META_WINDOW_WAYLAND (window);
+  MetaDisplay *display = meta_window_get_display (window);
+  MetaContext *context = meta_display_get_context (display);
+  MetaWaylandCompositor *compositor = meta_context_get_wayland_compositor (context);
+
+  toplevel_drag = meta_wayland_data_device_get_toplevel_drag (&compositor->seat->data_device);
+  if (!toplevel_drag || toplevel_drag->dragged_surface != wl_window->surface)
+    return NULL;
+  return toplevel_drag;
+}
+
 static void
 meta_window_wayland_init (MetaWindowWayland *wl_window)
 {
@@ -1179,6 +1195,8 @@ meta_window_wayland_finish_move_resize (MetaWindow              *window,
   gboolean is_client_resize;
   MetaWindowDrag *window_drag;
   MtkRectangle frame_rect;
+  MetaWindowActor *window_actor;
+  MetaWaylandToplevelDrag *toplevel_drag;
 
   /* new_geom is in the logical pixel coordinate space, but MetaWindow wants its
    * rects to represent what in turn will end up on the stage, i.e. we need to
@@ -1263,6 +1281,14 @@ meta_window_wayland_finish_move_resize (MetaWindow              *window,
         calculate_position (acked_configuration, &new_geom, &rect);
     }
 
+  toplevel_drag = get_toplevel_drag (window);
+  if (toplevel_drag && !is_window_being_resized && !window->mapped &&
+      rect.width > 0 && rect.height > 0)
+    {
+      meta_wayland_toplevel_drag_calc_origin_for_dragged_window (toplevel_drag,
+                                                                 &rect);
+    }
+
   rect.x += dx;
   rect.y += dy;
 
@@ -1295,6 +1321,15 @@ meta_window_wayland_finish_move_resize (MetaWindow              *window,
     gravity = meta_resize_gravity_from_grab_op (meta_window_drag_get_grab_op (window_drag));
   else
     gravity = META_GRAVITY_STATIC;
+
+  /* Force unconstrained move + northwest gravity when running toplevel drags */
+  if (toplevel_drag && surface == toplevel_drag->dragged_surface)
+    {
+      gravity = META_GRAVITY_NORTH_WEST;
+      window_actor = meta_window_actor_from_window (window);
+      meta_window_actor_set_tied_to_drag (window_actor, TRUE);
+    }
+
   meta_window_move_resize_internal (window,
                                     flags,
                                     META_PLACE_FLAG_NONE,