background: Fix math to calculate the interval from the duration

The math here before was incorrect. This is still wrong, as we're
looking at the total duration of the animation rather than the next
step.

https://bugzilla.gnome.org/show_bug.cgi?id=695882

diff --git a/js/ui/background.js b/js/ui/background.js
index 9e3e0099dc11394b4e704e557dc8d368096a0c78..bf8757eace520dde955c72c6451441a95fc71f77 100644 (file)
--- a/js/ui/background.js
+++ b/js/ui/background.js
@@ -442,8 +442,11 @@ const Background = new Lang.Class({
         if (!this._animation.duration)
             return;
 
+        let nSteps = 255 / ANIMATION_OPACITY_STEP_INCREMENT;
+        let timePerStep = (this._animation.duration * 1000) / nSteps;
+
         let interval = Math.max(ANIMATION_MIN_WAKEUP_INTERVAL * 1000,
-                                ANIMATION_OPACITY_STEP_INCREMENT / this._animation.duration);
+                                timePerStep);
         this._animationUpdateTimeoutId = GLib.timeout_add(GLib.PRIORITY_DEFAULT,
                                                       interval,
                                                       Lang.bind(this, function() {