gdk: always populate GDK_AXIS_{X,Y} in merged event history

Since GdkTimeCoord stores only axis values, prior to this change,
if a device didn't report GDK_AXIS_X or GDK_AXIS_Y, the history
attached to merged motion events wouldn't contain any positional
information.

Commit 6012276093ea10dc0913c38d9123c37b08a20264 already addressed
this issue for devices without tools by storing the event position
in GdkTimeCoord using GDK_AXIS_X and GDK_AXIS_Y and augmenting the
GdkTimeCoord's axis bitmask accordingly.

This change generalizes that workaround to all devices. Note that
if a device DOES report values for GDK_AXIS_X and GDK_AXIS_Y, those
values won't be overwritten.

Closes #4809

diff --git a/gdk/gdkevents.c b/gdk/gdkevents.c
index 2ce9b8b72a3d8702cf4c3a1d2a1322b93f85c801..cc06e5e0c0f0992016fee0ca14fb31f7a199f82d 100644 (file)
--- a/gdk/gdkevents.c
+++ b/gdk/gdkevents.c
@@ -757,15 +757,21 @@ gdk_motion_event_push_history (GdkEvent *event,
 
   memset (&hist, 0, sizeof (GdkTimeCoord));
   hist.time = gdk_event_get_time (history_event);
+
   if (tool)
     {
       hist.flags = gdk_device_tool_get_axes (tool);
       for (i = GDK_AXIS_X; i < GDK_AXIS_LAST; i++)
         gdk_event_get_axis (history_event, i, &hist.axes[i]);
     }
-  else
+
+  /* GdkTimeCoord has no dedicated fields to record event position. For plain
+   * pointer events, and for tools which don't report GDK_AXIS_X/GDK_AXIS_Y
+   * on their own, we surface the position using the X and Y input axes.
+   */
+  if (!(hist.flags & GDK_AXIS_FLAG_X) || !(hist.flags & GDK_AXIS_FLAG_Y))
     {
-      hist.flags = GDK_AXIS_FLAG_X | GDK_AXIS_FLAG_Y;
+      hist.flags |= GDK_AXIS_FLAG_X | GDK_AXIS_FLAG_Y;
       gdk_event_get_position (history_event, &hist.axes[GDK_AXIS_X], &hist.axes[GDK_AXIS_Y]);
     }