[gnome-shell] tweener: make timeline loop indefinitely

[Ray Strode <halfline src gnome org>]

commit 207abe9a2c1867fda6383e5609c4d7e8c794a8ce
Author: Ray Strode <rstrode redhat com>
Date:   Thu Feb 16 13:29:46 2012 -0500

    tweener: make timeline loop indefinitely
    
    Tweener uses a clutter timeline to manage all active animations
    running at a given moment.  The timeline is mopped up when no
    animations are going any more.
    
    Clutter requires timelines to have a finite duration, but since
    animations can happen at any moment, no fixed duration can
    accomodate the shell's needs.
    
    To combat this problem, the tweener code picks a relatively
    long duration: 1000 seconds. No string of animations should take
    that long, so, in theory, that should be good enough.
    
    Unfortunately, this tactic fails, in practice, when the user
    suspends their machine, or VT switches.  An animation can take
    much longer than 1000 seconds (~16 minutes) to complete in those
    cases.  When the user resumes, or VT switches back the timeline
    completes immediately (since it's already late) and tweener
    never notices that the timeline stops ticking.
    
    This commit changes the tweener timeline to automatically loop
    back to 0 after completing, so that despite its fixed duration
    property, it effectively never stops. Since the timeline loops,
    its concept of elapsed time no longer increases monotonically,
    so we now ignore it and track time ourselves with
    GLib.get_monotonic_time().
    
    This partially reverts commit
    35764fa09e4341e79732409c4e74c226d19f780f.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=653833

 js/ui/tweener.js |   14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)
---
diff --git a/js/ui/tweener.js b/js/ui/tweener.js
index 7d98a65..ecfdb20 100644
--- a/js/ui/tweener.js
+++ b/js/ui/tweener.js
@@ -1,6 +1,7 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 
 const Clutter = imports.gi.Clutter;
+const GLib = imports.gi.GLib;
 const Lang = imports.lang;
 const Mainloop = imports.mainloop;
 const Shell = imports.gi.Shell;
@@ -209,9 +210,14 @@ const ClutterFrameTicker = new Lang.Class({
 
     _init : function() {
         // We don't have a finite duration; tweener will tell us to stop
-        // when we need to stop, so use 1000 seconds as "infinity"
+        // when we need to stop, so use 1000 seconds as "infinity", and
+        // set the timeline to loop. Doing this means we have to track
+        // time ourselves, since clutter timeline's time will cycle
+        // instead of strictly increase.
         this._timeline = new Clutter.Timeline({ duration: 1000*1000 });
+        this._timeline.set_loop(true);
         this._startTime = -1;
+        this._currentTime = -1;
 
         this._timeline.connect('new-frame', Lang.bind(this,
             function(timeline, frame) {
@@ -234,17 +240,18 @@ const ClutterFrameTicker = new Lang.Class({
         // That looks bad, so we always start at the first frame of the
         // animation then only do frame dropping from there.
         if (this._startTime < 0)
-            this._startTime = this._timeline.get_elapsed_time();
+            this._startTime = GLib.get_monotonic_time() / 1000.0;
 
         // currentTime is in milliseconds
         let perf_log = Shell.PerfLog.get_default();
+        this._currentTime = GLib.get_monotonic_time() / 1000.0 - this._startTime;
         perf_log.event("tweener.framePrepareStart");
         this.emit('prepare-frame');
         perf_log.event("tweener.framePrepareDone");
     },
 
     getTime : function() {
-        return this._timeline.get_elapsed_time();
+        return this._currentTime;
     },
 
     start : function() {
@@ -257,6 +264,7 @@ const ClutterFrameTicker = new Lang.Class({
     stop : function() {
         this._timeline.stop();
         this._startTime = -1;
+        this._currentTime = -1;
         global.end_work();
     }
 });