[mutter] clutter/frame-clock: Simplify early presented event handling

[Marge Bot <marge-bot src gnome org>]

commit 01846ffd913c68d848fb415b11b0ca290d50963e
Author: Dor Askayo <dor askayo gmail com>
Date:   Sat Mar 13 12:55:09 2021 +0200

    clutter/frame-clock: Simplify early presented event handling
    
    A few calculations and assignments are done unnecessarily when the
    last next presentation time is invalid. This increases the cognitive
    complexity of the function for no reason.
    
    No change in behavior.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2486>

 clutter/clutter/clutter-frame-clock.c | 51 ++++++++++++++++++-----------------
 1 file changed, 27 insertions(+), 24 deletions(-)
---
diff --git a/clutter/clutter/clutter-frame-clock.c b/clutter/clutter/clutter-frame-clock.c
index cf740adc3b..b223b85452 100644
--- a/clutter/clutter/clutter-frame-clock.c
+++ b/clutter/clutter/clutter-frame-clock.c
@@ -407,8 +407,6 @@ calculate_next_update_time_us (ClutterFrameClock *frame_clock,
   int64_t refresh_interval_us;
   int64_t min_render_time_allowed_us;
   int64_t max_render_time_allowed_us;
-  int64_t last_next_presentation_time_us;
-  int64_t time_since_last_next_presentation_time_us;
   int64_t next_presentation_time_us;
   int64_t next_update_time_us;
 
@@ -510,29 +508,34 @@ calculate_next_update_time_us (ClutterFrameClock *frame_clock,
         refresh_interval_us;
     }
 
-  /*
-   * Skip one interval if we got an early presented event.
-   *
-   *        last frame this was last_presentation_time
-   *       /       frame_clock->next_presentation_time_us
-   *      /       /
-   * |---|-o-----|-x----->
-   *       |       \
-   *       \        next_presentation_time_us is thus right after the last one
-   *        but got an unexpected early presentation
-   *             \_/
-   *             time_since_last_next_presentation_time_us
-   *
-   */
-  last_next_presentation_time_us = frame_clock->next_presentation_time_us;
-  time_since_last_next_presentation_time_us =
-    next_presentation_time_us - last_next_presentation_time_us;
-  if (frame_clock->is_next_presentation_time_valid &&
-      time_since_last_next_presentation_time_us > 0 &&
-      time_since_last_next_presentation_time_us < (refresh_interval_us / 2))
+  if (frame_clock->is_next_presentation_time_valid)
     {
-      next_presentation_time_us =
-        frame_clock->next_presentation_time_us + refresh_interval_us;
+      int64_t last_next_presentation_time_us;
+      int64_t time_since_last_next_presentation_time_us;
+
+      /*
+       * Skip one interval if we got an early presented event.
+       *
+       *        last frame this was last_presentation_time
+       *       /       frame_clock->next_presentation_time_us
+       *      /       /
+       * |---|-o-----|-x----->
+       *       |       \
+       *       \        next_presentation_time_us is thus right after the last one
+       *        but got an unexpected early presentation
+       *             \_/
+       *             time_since_last_next_presentation_time_us
+       *
+       */
+      last_next_presentation_time_us = frame_clock->next_presentation_time_us;
+      time_since_last_next_presentation_time_us =
+        next_presentation_time_us - last_next_presentation_time_us;
+      if (time_since_last_next_presentation_time_us > 0 &&
+          time_since_last_next_presentation_time_us < (refresh_interval_us / 2))
+        {
+          next_presentation_time_us =
+            frame_clock->next_presentation_time_us + refresh_interval_us;
+        }
     }
 
   while (next_presentation_time_us < now_us + min_render_time_allowed_us)