[gtk+] gdk: Implement motion history as motion event data

[Carlos Garnacho <carlosg src gnome org>]

commit ea216accd7b136a5537e567fce7a165cb41cf9c0
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Oct 31 12:37:50 2017 +0100

    gdk: Implement motion history as motion event data
    
    In the motion compression phase the coalesced events will be saved
    as a GdkTimeCoord on the motion event that shall be delivered.
    
    For simplicity (and because history doesn't make much sense otherwise)
    event history is only recorded while there are buttons pressed, this
    also tidily ensures that those coalesced events would have the same
    target widget on the gtk side than the delivered one, because of
    implicit grabs.

 gdk/gdkevents.c        |   56 ++++++++++++++++++++++++++++++++++++++++++++++++
 gdk/gdkevents.h        |    1 +
 gdk/gdkeventsprivate.h |    1 +
 3 files changed, 58 insertions(+), 0 deletions(-)
---
diff --git a/gdk/gdkevents.c b/gdk/gdkevents.c
index 19bf7e6..8b3b981 100644
--- a/gdk/gdkevents.c
+++ b/gdk/gdkevents.c
@@ -337,13 +337,37 @@ _gdk_event_unqueue (GdkDisplay *display)
   return event;
 }
 
+static void
+gdk_event_push_history (GdkEvent       *event,
+                        const GdkEvent *history_event)
+{
+  GdkTimeCoord *hist;
+  GdkDevice *device;
+  gint i, n_axes;
+
+  g_assert (event->any.type == GDK_MOTION_NOTIFY);
+  g_assert (history_event->any.type == GDK_MOTION_NOTIFY);
+
+  hist = g_new0 (GdkTimeCoord, 1);
+
+  device = gdk_event_get_device (history_event);
+  n_axes = gdk_device_get_n_axes (device);
+
+  for (i = 0; i <= MIN (n_axes, GDK_MAX_TIMECOORD_AXES); i++)
+    gdk_event_get_axis (history_event, i, &hist->axes[i]);
+
+  event->motion.history = g_list_prepend (event->motion.history, hist);
+}
+
 void
 _gdk_event_queue_handle_motion_compression (GdkDisplay *display)
 {
   GList *tmp_list;
   GList *pending_motions = NULL;
+  GList *history = NULL;
   GdkWindow *pending_motion_window = NULL;
   GdkDevice *pending_motion_device = NULL;
+  GdkEvent *last_motion = NULL;
 
   /* If the last N events in the event queue are motion notify
    * events for the same window, drop all but the last */
@@ -371,6 +395,9 @@ _gdk_event_queue_handle_motion_compression (GdkDisplay *display)
       if (!event->any.window->event_compression)
         break;
 
+      if (!last_motion)
+        last_motion = event;
+
       pending_motion_window = event->any.window;
       pending_motion_device = event->any.device;
       pending_motions = tmp_list;
@@ -381,6 +408,15 @@ _gdk_event_queue_handle_motion_compression (GdkDisplay *display)
   while (pending_motions && pending_motions->next != NULL)
     {
       GList *next = pending_motions->next;
+
+      history = g_list_prepend (history, pending_motions->data);
+
+      if (last_motion &&
+          (last_motion->motion.state &
+           (GDK_BUTTON1_MASK | GDK_BUTTON2_MASK | GDK_BUTTON3_MASK |
+            GDK_BUTTON4_MASK | GDK_BUTTON5_MASK)))
+        gdk_event_push_history (last_motion, pending_motions->data);
+
       gdk_event_free (pending_motions->data);
       display->queued_events = g_list_delete_link (display->queued_events,
                                                    pending_motions);
@@ -558,6 +594,12 @@ gdk_event_get_pointer_emulated (GdkEvent *event)
   return (event->any.flags & GDK_EVENT_POINTER_EMULATED) != 0;
 }
 
+static GdkTimeCoord *
+copy_time_coord (const GdkTimeCoord *coord)
+{
+  return g_memdup (coord, sizeof (GdkTimeCoord));
+}
+
 /**
  * gdk_event_copy:
  * @event: a #GdkEvent
@@ -642,6 +684,12 @@ gdk_event_copy (const GdkEvent *event)
                                            sizeof (gdouble) * gdk_device_get_n_axes (event->any.device));
       if (event->motion.tool)
         g_object_ref (new_event->motion.tool);
+
+      if (event->motion.history)
+        {
+          new_event->motion.history = g_list_copy_deep (event->motion.history,
+                                                        (GCopyFunc) copy_time_coord, NULL);
+        }
       break;
 
     default:
@@ -718,6 +766,7 @@ gdk_event_finalize (GObject *object)
     case GDK_MOTION_NOTIFY:
       g_clear_object (&event->motion.tool);
       g_free (event->motion.axes);
+      g_list_free_full (event->motion.history, g_free);
       break;
 
     default:
@@ -2623,3 +2672,10 @@ gdk_event_get_axes (GdkEvent  *event,
   return FALSE;
 }
 
+GList *
+gdk_event_get_history (const GdkEvent *event)
+{
+  if (event->any.type != GDK_MOTION_NOTIFY)
+    return NULL;
+  return g_list_reverse (g_list_copy (event->motion.history));
+}
diff --git a/gdk/gdkevents.h b/gdk/gdkevents.h
index db4b779..65a00cc 100644
--- a/gdk/gdkevents.h
+++ b/gdk/gdkevents.h
@@ -716,6 +716,7 @@ GDK_AVAILABLE_IN_3_92
 gboolean       gdk_event_get_axes      (GdkEvent  *event,
                                         gdouble  **axes,
                                         guint     *n_axes);
+GList        * gdk_event_get_history   (const GdkEvent  *event);
 
 G_END_DECLS
 
diff --git a/gdk/gdkeventsprivate.h b/gdk/gdkeventsprivate.h
index bb3bb47..b9fc789 100644
--- a/gdk/gdkeventsprivate.h
+++ b/gdk/gdkeventsprivate.h
@@ -121,6 +121,7 @@ struct _GdkEventMotion
   gint16 is_hint;
   GdkDeviceTool *tool;
   gdouble x_root, y_root;
+  GList *history;
 };
 
 /**