From: =?utf-8?b?Ik1hcmNvIFRyZXZpc2FuIChUcmV2acOxbyki?= <mail@3v1n0.net>
Date: Wed, 6 Apr 2022 18:28:42 +0200
Subject: wayland-data-device: Allow any drag timestamp as drag start serial

In some scenarios under wayland DnD may not work because the start-drag
serial is not matching the one we expect for the pointer that we set
when handling the button event.

This is because since commit 26676a82 we're repeatedly pinging the
windows at each event to ensure that they're still alive, but we're
using the event timestamp for that, and this makes wayland to use such
value as the start-drag serial.

To avoid this, let's keep track of all the grab timestamps we got while
dragging and accept a serial to match any of these.

Bug: https://gitlab.gnome.org/GNOME/mutter/-/issues/2216
Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/mutter/+bug/1964541
---
 src/wayland/meta-wayland-data-device.c | 15 ++++++++++++++-
 src/wayland/meta-wayland-pointer.c     |  9 +++++++++
 src/wayland/meta-wayland-pointer.h     |  1 +
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/wayland/meta-wayland-data-device.c b/src/wayland/meta-wayland-data-device.c
index 054bb44..5f5bb67 100644
--- a/src/wayland/meta-wayland-data-device.c
+++ b/src/wayland/meta-wayland-data-device.c
@@ -695,6 +695,15 @@ meta_wayland_data_device_end_drag (MetaWaylandDataDevice *data_device)
     data_device_end_drag_grab (data_device->current_grab);
 }
 
+static int
+compare_times (gconstpointer a, gconstpointer b)
+{
+  const uint32_t *_a = a;
+  const uint32_t *_b = b;
+
+  return *_a - *_b;
+}
+
 static void
 data_device_start_drag (struct wl_client  *client,
                         struct wl_resource *resource,
@@ -716,7 +725,11 @@ data_device_start_drag (struct wl_client  *client,
     return;
 
   if (seat->pointer->button_count == 0 ||
-      seat->pointer->grab_serial != serial ||
+      (seat->pointer->grab_serial != serial &&
+       !g_array_binary_search (seat->pointer->grab_times,
+                               &serial,
+                               compare_times,
+                               NULL)) ||
       !seat->pointer->focus_surface ||
       seat->pointer->focus_surface != surface)
     return;
diff --git a/src/wayland/meta-wayland-pointer.c b/src/wayland/meta-wayland-pointer.c
index 9374117..d891755 100644
--- a/src/wayland/meta-wayland-pointer.c
+++ b/src/wayland/meta-wayland-pointer.c
@@ -722,6 +722,9 @@ notify_motion (MetaWaylandPointer *pointer,
                const ClutterEvent *event)
 {
   pointer->grab->interface->motion (pointer->grab, event);
+
+  if (pointer->grab_times)
+    g_array_append_val (pointer->grab_times, event->any.time);
 }
 
 static void
@@ -742,8 +745,14 @@ handle_button_event (MetaWaylandPointer *pointer,
     {
       pointer->grab_button = clutter_event_get_button (event);
       pointer->grab_time = clutter_event_get_time (event);
+      pointer->grab_times = g_array_new (FALSE, TRUE, sizeof (uint32_t));
+      g_array_append_val (pointer->grab_times, event->any.time);
       clutter_event_get_coords (event, &pointer->grab_x, &pointer->grab_y);
     }
+  else if (event->type == CLUTTER_BUTTON_RELEASE && pointer->button_count == 0)
+    {
+      g_clear_pointer (&pointer->grab_times, g_array_unref);
+    }
 
   pointer->grab->interface->button (pointer->grab, event);
 
diff --git a/src/wayland/meta-wayland-pointer.h b/src/wayland/meta-wayland-pointer.h
index f7b91a5..ea47f4e 100644
--- a/src/wayland/meta-wayland-pointer.h
+++ b/src/wayland/meta-wayland-pointer.h
@@ -85,6 +85,7 @@ struct _MetaWaylandPointer
   guint32 grab_button;
   guint32 grab_serial;
   guint32 grab_time;
+  GArray* grab_times;
   float grab_x, grab_y;
 
   ClutterInputDevice *device;