protected void UpdateActorWithAlpha(ClutterFlowBaseActor actor, double alpha)
        {
            float ratio = Math.Min(0.75f * (float)coverManager.Timeline.Delta / (float)coverManager.VisibleCovers, 1.25f);

            OffsetRotationAngle = (float)((rotationAngle / 5) * ratio);
            OffsetCenterX       = -(float)((CenterMargin / 2) * ratio);
            OffsetZNear         = (int)(-(ZNear - ZFar) * 1.5 * ratio);
            if (coverManager.Timeline.Direction != TimelineDirection.Forward)
            {
                OffsetRotationAngle = -OffsetRotationAngle;
                OffsetCenterX       = -OffsetCenterX;
            }

            actor.SetScale(coverWidth / actor.Width, coverWidth / actor.Width);
            if (alpha != 0 || alpha != 1)
            {
                //if (!visible_actors.Contains (actor)) visible_actors.Add (actor);
                actor.Show();
                if (alpha < AlphaStep)
                {
                    MoveAndFadeOutActor(actor, (float)(alpha / AlphaStep), true);
                }
                else if (alpha >= AlphaStep && alpha <= 0.5 - AlphaStep)
                {
                    MoveActorSideways(actor, (float)((alpha - AlphaStep) / (0.5f - 2 * AlphaStep)), true);
                }
                else if (alpha > 0.5f - AlphaStep && alpha < 0.5f + AlphaStep)
                {
                    MoveAndRotateActorCentrally(actor, (float)((alpha - 0.5f) / AlphaStep));
                }
                else if (alpha >= 0.5f + AlphaStep && alpha <= 1 - AlphaStep)
                {
                    MoveActorSideways(actor, (float)((1 - AlphaStep - alpha) / (0.5f - 2 * AlphaStep)), false);
                }
                else if (alpha > 1 - AlphaStep)
                {
                    MoveAndFadeOutActor(actor, (float)((1 - alpha) / AlphaStep), false);
                }
            }
            else
            {
                //if (visible_actors.Contains (actor)) visible_actors.Remove (actor);
                actor.Hide();
            }
        }
 protected void HideActor(ClutterFlowBaseActor actor)
 {
     actor.Hide();
 }