compositor-wayland: ignore frame callback's time

Weston running the Wayland backend is nested. The parent compositor uses
an unknown clock for the frame callback timestamps. This is quite likely
a different clock from what the nested Weston chose as its presentation
clock.

This means we cannot reasonably read the presentation clock and assume
it has any relation to the timestamp got from the frame callback. In
fact, this was seen to cause absurd repaint delays, trigger the insanity
check, reduce fraterate, etc. problems, because we assume we can read
the clock and compute the remaining repaint delay.

As we can't use the timestamp, ignore it, and read our own presentation
clock instead.

The X11 backend does not suffer from this, because there the parent
window system never provides us any timestamps, so we always read our
own clock.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>
Acked-by: Giulio Camuffo <giuliocamuffo@gmail.com>

src/compositor-wayland.c

@@ -312,8 +312,15 @@ frame_done(void *data, struct wl_callback *callback, uint32_t time)
 	wl_callback_destroy(callback);
 
 	/* XXX: use the presentation extension for proper timings */
-	ts.tv_sec = time / 1000;
-	ts.tv_nsec = (time % 1000) * 1000000;
+
+	/*
+	 * This is the fallback case, where Presentation extension is not
+	 * available from the parent compositor. We do not know the base for
+	 * 'time', so we cannot feed it to finish_frame(). Do the only thing
+	 * we can, and pretend finish_frame time is when we process this
+	 * event.
+	 */
+	weston_compositor_read_presentation_clock(output->compositor, &ts);
 	weston_output_finish_frame(output, &ts, 0);
 }