Fix zero-duration animations running Backwards.

If you set the duration of any variant or property animation to 0,
its progress will be stuck at 1 (0..1), and its "end" value set on
the target object, after start() has been called. If you change the
direction of the animation to QAbstractAnimation::Backward, you
would expect the progress to be 0 after start. Instead it's still
1; the code seems to assume that if the duration is 0, the
progress must be 1 always.

The fix is that if the duration is 0, the direction is checked to
determine whether progress should be 0 (Backward) or 1 (Forward).

Task-number: QTBUG-27969
Change-Id: Ibeca084bbbce41df1dca7b7d96c15b6b54394996
(cherry-picked from qtbase/f3597af5adcd2275503e9e4bfb425549f9ab3ced)
Reviewed-by: Thierry Bastian <thierryb@filewave.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/corelib/animation/qvariantanimation.cpp b/src/corelib/animation/qvariantanimation.cpp
index 355207e52b..f8d7ea527b 100644
--- a/src/corelib/animation/qvariantanimation.cpp
+++ b/src/corelib/animation/qvariantanimation.cpp
@@ -237,7 +237,8 @@ void QVariantAnimationPrivate::recalculateCurrentInterval(bool force/*=false*/)
     if ((keyValues.count() + (defaultStartEndValue.isValid() ? 1 : 0)) < 2)
         return;
 
-    const qreal progress = easing.valueForProgress(((duration == 0) ? qreal(1) : qreal(currentTime) / qreal(duration)));
+    const qreal endProgress = (direction == QAbstractAnimation::Forward) ? qreal(1) : qreal(0);
+    const qreal progress = easing.valueForProgress(((duration == 0) ? endProgress : qreal(currentTime) / qreal(duration)));
 
     //0 and 1 are still the boundaries
     if (force || (currentInterval.start.first > 0 && progress < currentInterval.start.first)