From e4542a6495681ef6e29d348ac70108f98bfd1c62 Mon Sep 17 00:00:00 2001
From: Carlos Garnacho <carlosg@gnome.org>
Date: Thu, 25 Jan 2024 12:38:01 +0100
Subject: [PATCH] compositor: Add MetaWindowDrag API to add a hint on the grab
 coordinates

This is added as a hint so that the caller can optionally use it, e.g.
in the case that a window drag is driven by the mouse. This will be used
to more accurately follow the drag position, other than starting at the
current pointer position.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3546>
---
 src/compositor/meta-window-drag.c | 17 +++++++++++++++++
 src/compositor/meta-window-drag.h |  3 +++
 2 files changed, 20 insertions(+)

diff --git a/src/compositor/meta-window-drag.c b/src/compositor/meta-window-drag.c
index 53b81c348..576bfb37c 100644
--- a/src/compositor/meta-window-drag.c
+++ b/src/compositor/meta-window-drag.c
@@ -56,6 +56,8 @@ struct _MetaWindowDrag {
   MetaGrabOp grab_op;
   ClutterGrab *grab;
 
+  graphene_point_t pos_hint;
+
   ClutterInputDevice *leading_device;
   ClutterEventSequence *leading_touch_sequence;
   double anchor_rel_x;
@@ -79,6 +81,7 @@ struct _MetaWindowDrag {
 
   guint tile_preview_timeout_id;
   guint preview_tile_mode : 2;
+  guint pos_hint_set : 1;
 };
 
 G_DEFINE_FINAL_TYPE (MetaWindowDrag, meta_window_drag, G_TYPE_OBJECT)
@@ -1781,6 +1784,11 @@ meta_window_drag_begin (MetaWindowDrag       *window_drag,
     {
       warp_grab_pointer (window_drag, window, grab_op, &root_x, &root_y);
     }
+  else if (window_drag->pos_hint_set)
+    {
+      root_x = window_drag->pos_hint.x;
+      root_y = window_drag->pos_hint.y;
+    }
   else
     {
       ClutterBackend *clutter_backend = meta_backend_get_clutter_backend (backend);
@@ -1917,3 +1925,12 @@ meta_window_drag_update_edges (MetaWindowDrag *window_drag)
 {
   meta_window_drag_edge_resistance_cleanup (window_drag);
 }
+
+void
+meta_window_drag_set_position_hint (MetaWindowDrag   *window_drag,
+                                    graphene_point_t *pos_hint)
+{
+  window_drag->pos_hint_set = pos_hint != NULL;
+  if (pos_hint)
+    window_drag->pos_hint = *pos_hint;
+}
diff --git a/src/compositor/meta-window-drag.h b/src/compositor/meta-window-drag.h
index 3f48dcc09..5fac435b7 100644
--- a/src/compositor/meta-window-drag.h
+++ b/src/compositor/meta-window-drag.h
@@ -43,3 +43,6 @@ MetaWindow * meta_window_drag_get_window (MetaWindowDrag *window_drag);
 MetaGrabOp meta_window_drag_get_grab_op (MetaWindowDrag *window_drag);
 
 void meta_window_drag_update_edges (MetaWindowDrag *window_drag);
+
+void meta_window_drag_set_position_hint (MetaWindowDrag   *window_drag,
+                                         graphene_point_t *pos_hint);