[libdazzle] animation: always use the same clock when determine offset

[Christian Hergert <chergert src gnome org>]

commit 91c55363536c10a1b0f1030bfa17203466f10852
Author: Christian Hergert <chergert redhat com>
Date:   Tue Feb 20 22:38:17 2018 -0800

    animation: always use the same clock when determine offset
    
    We want to ensure we only ever compare values that come from the same
    clock. So this changes things around so that we always use the frame
    clock values when a frame clock is in use.

 src/animation/dzl-animation.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)
---
diff --git a/src/animation/dzl-animation.c b/src/animation/dzl-animation.c
index 5ccccea..2023f51 100644
--- a/src/animation/dzl-animation.c
+++ b/src/animation/dzl-animation.c
@@ -52,8 +52,9 @@ struct _DzlAnimation
   GInitiallyUnowned  parent_instance;
 
   gpointer           target;              /* Target object to animate */
-  guint64            begin_msec;          /* Time in which animation started */
-  guint              duration_msec;       /* Duration of animation */
+  gint64             begin_time;          /* Time in which animation started */
+  gint64             end_time;            /* Deadline for the animation */
+  guint              duration_msec;       /* Duration in milliseconds */
   guint              mode;                /* Tween mode */
   gulong             tween_handler;       /* GSource or signal handler */
   gulong             after_paint_handler; /* signal handler */
@@ -312,9 +313,6 @@ static gdouble
 dzl_animation_get_offset (DzlAnimation *animation,
                           gint64        frame_time)
 {
-  gdouble offset;
-  gint64 frame_msec;
-
   g_assert (DZL_IS_ANIMATION (animation));
 
   if (frame_time == 0)
@@ -325,12 +323,14 @@ dzl_animation_get_offset (DzlAnimation *animation,
         frame_time = g_get_monotonic_time ();
     }
 
-  frame_msec = frame_time / 1000L;
+  frame_time = CLAMP (frame_time, animation->begin_time, animation->end_time);
 
-  offset = (gdouble) (frame_msec - animation->begin_msec) /
-           (gdouble) MAX (animation->duration_msec, 1);
+  if (frame_time == animation->begin_time)
+    return 0.0;
+  else if (frame_time == animation->end_time)
+    return 1.0;
 
-  return CLAMP (offset, 0.0, 1.0);
+  return (frame_time - animation->begin_time) / (gdouble)(animation->duration_msec * 1000L);
 }
 
 
@@ -623,10 +623,11 @@ dzl_animation_start (DzlAnimation *animation)
    * We want the real current time instead of the GdkFrameClocks current time
    * because if the clock was asleep, it could be innaccurate.
    */
-  animation->begin_msec = g_get_monotonic_time () / 1000UL;
 
   if (animation->frame_clock)
     {
+      animation->begin_time = gdk_frame_clock_get_frame_time (animation->frame_clock);
+      animation->end_time = animation->begin_time + (animation->duration_msec * 1000L);
       animation->tween_handler =
         g_signal_connect (animation->frame_clock,
                           "update",
@@ -641,6 +642,8 @@ dzl_animation_start (DzlAnimation *animation)
     }
   else
     {
+      animation->begin_time = g_get_monotonic_time ();
+      animation->end_time = animation->begin_time + (animation->duration_msec * 1000L);
       animation->tween_handler = dzl_frame_source_add (FALLBACK_FRAME_RATE,
                                                        dzl_animation_timeout_cb,
                                                        animation);