[mutter] core: Unset "pointer emulating" sequence lazily

[Carlos Garnacho <carlosg src gnome org>]

commit 96b5042dda6a46bee93867340b85ea176c8070b1
Author: Carlos Garnacho <carlosg gnome org>
Date:   Fri Oct 16 15:13:40 2015 +0200

    core: Unset "pointer emulating" sequence lazily
    
    Unsetting it in meta_display_handle_event() will make the pointer
    emulation checks fail on TOUCH_END event handlers across clutter
    actors, the sequence should still be considered as pointer emulating
    at that time.
    
    As we don't have a way to hook this post clutter event handling,
    instead unset/reset it lazily on the next pointer emulating TOUCH_BEGIN
    event, the checks would already fail on other sequences, even if the
    pointer emulating touch ended earlier. The only extra thing we need
    to take care about is sequence collision, at which point it's safe to
    just unset the stored sequence if its new incarnation isn't flagged/
    deemed as pointer emulating.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=756754

 src/core/events.c |   28 +++++++++++++++++++---------
 1 files changed, 19 insertions(+), 9 deletions(-)
---
diff --git a/src/core/events.c b/src/core/events.c
index 25e0719..7a1cbc9 100644
--- a/src/core/events.c
+++ b/src/core/events.c
@@ -182,10 +182,25 @@ meta_display_handle_event (MetaDisplay        *display,
   sequence = clutter_event_get_event_sequence (event);
 
   /* Set the pointer emulating sequence on touch begin, if eligible */
-  if (event->type == CLUTTER_TOUCH_BEGIN &&
-      !display->pointer_emulating_sequence &&
-      sequence_is_pointer_emulated (display, event))
-    display->pointer_emulating_sequence = sequence;
+  if (event->type == CLUTTER_TOUCH_BEGIN)
+    {
+      if (sequence_is_pointer_emulated (display, event))
+        {
+          /* This is the new pointer emulating sequence */
+          display->pointer_emulating_sequence = sequence;
+        }
+      else if (display->pointer_emulating_sequence == sequence)
+        {
+          /* This sequence was "pointer emulating" in a prior incarnation,
+           * but now it isn't. We unset the pointer emulating sequence at
+           * this point so the current sequence is not mistaken as pointer
+           * emulating, while we've ensured that it's been deemed
+           * "pointer emulating" throughout all of the event processing
+           * of the previous incarnation.
+           */
+          display->pointer_emulating_sequence = NULL;
+        }
+    }
 
 #ifdef HAVE_WAYLAND
   MetaWaylandCompositor *compositor = NULL;
@@ -335,11 +350,6 @@ meta_display_handle_event (MetaDisplay        *display,
     }
 #endif
 
-  /* Unset the pointer emulating sequence after its end event is processed */
-  if (event->type == CLUTTER_TOUCH_END &&
-      display->pointer_emulating_sequence == sequence)
-    display->pointer_emulating_sequence = NULL;
-
   display->current_time = CurrentTime;
   return bypass_clutter;
 }