[gtk+/wip/carlosg/event-as-object: 15/23] gdk: Implement motion history as motion event data

[Carlos Garnacho <carlosg src gnome org>]

commit 35511706ffa7b123897e2aa1e140e0a3b4ab7e50
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 eeb172d..2deb1a2 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);
@@ -687,6 +723,12 @@ 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
@@ -771,6 +813,12 @@ 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;
 
     case GDK_OWNER_CHANGE:
@@ -861,6 +909,7 @@ 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;
       
     case GDK_OWNER_CHANGE:
@@ -2960,3 +3009,10 @@ 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 28026c7..56d0f1e 100644
--- a/gdk/gdkevents.h
+++ b/gdk/gdkevents.h
@@ -786,6 +786,7 @@ 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 9a87b73..0810682 100644
--- a/gdk/gdkeventsprivate.h
+++ b/gdk/gdkeventsprivate.h
@@ -141,6 +141,7 @@ struct _GdkEventMotion
   gint16 is_hint;
   GdkDeviceTool *tool;
   gdouble x_root, y_root;
+  GList *history;
 };
 
 /**