[gtk: 1/2] gdk: always populate GDK_AXIS_{X, Y} in merged event history

[Matthias Clasen <matthiasc src gnome org>]

commit 0c44851848d3871e61dd7413260eab81e36cb9c0
Author: Hemidark <support hemidark net>
Date:   Tue Apr 5 14:56:33 2022 -0700

    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

 gdk/gdkevents.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)
---
diff --git a/gdk/gdkevents.c b/gdk/gdkevents.c
index 2ce9b8b72a..cc06e5e0c0 100644
--- 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]);
     }