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>

2 files changed, 47 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)
diff --git a/tests/auto/qpropertyanimation/tst_qpropertyanimation.cpp b/tests/auto/qpropertyanimation/tst_qpropertyanimation.cpp
index 21c05921b9..a263e2ef6f 100644
--- a/tests/auto/qpropertyanimation/tst_qpropertyanimation.cpp
+++ b/tests/auto/qpropertyanimation/tst_qpropertyanimation.cpp
@@ -124,6 +124,7 @@ private slots:
     void setStartEndValues_data();
     void setStartEndValues();
     void zeroDurationStart();
+    void zeroDurationForwardBackward();
     void operationsInStates_data();
     void operationsInStates();
     void oneKeyValue();
@@ -879,6 +880,50 @@ void tst_QPropertyAnimation::zeroDurationStart()
     QCOMPARE(qVariantValue<QAbstractAnimation::State>(secondChange.first()), QAbstractAnimation::Stopped);
 }
 
+void tst_QPropertyAnimation::zeroDurationForwardBackward()
+{
+    QObject o; o.setProperty("test", 1);
+    QObject o2; o2.setProperty("test", 2);
+    QObject o3; o3.setProperty("test", 3);
+    QObject o4; o4.setProperty("test", 4);
+    QPropertyAnimation prop(&o, "test"); prop.setDuration(0); prop.setStartValue(1); prop.setEndValue(2);
+
+    prop.start();
+    QCOMPARE(o.property("test").toInt(), 2);
+    prop.setDirection(QAbstractAnimation::Backward);
+    prop.start();
+    QCOMPARE(o.property("test").toInt(), 1);
+
+    prop.setDirection(QAbstractAnimation::Forward);
+    QPropertyAnimation prop2(&o2, "test"); prop2.setDuration(0); prop2.setStartValue(2); prop2.setEndValue(3);
+    QPropertyAnimation prop3(&o3, "test"); prop3.setDuration(0); prop3.setStartValue(3); prop3.setEndValue(4);
+    QPropertyAnimation prop4(&o4, "test"); prop4.setDuration(0); prop4.setStartValue(4); prop4.setEndValue(5);
+    QSequentialAnimationGroup group;
+    group.addAnimation(&prop);
+    group.addAnimation(&prop2);
+    group.addAnimation(&prop3);
+    group.addAnimation(&prop4);
+    group.start();
+
+    QCOMPARE(o.property("test").toInt(), 2);
+    QCOMPARE(o2.property("test").toInt(), 3);
+    QCOMPARE(o3.property("test").toInt(), 4);
+    QCOMPARE(o4.property("test").toInt(), 5);
+
+    group.setDirection(QAbstractAnimation::Backward);
+    group.start();
+
+    QCOMPARE(o.property("test").toInt(), 1);
+    QCOMPARE(o2.property("test").toInt(), 2);
+    QCOMPARE(o3.property("test").toInt(), 3);
+    QCOMPARE(o4.property("test").toInt(), 4);
+
+    group.removeAnimation(&prop);
+    group.removeAnimation(&prop2);
+    group.removeAnimation(&prop3);
+    group.removeAnimation(&prop4);
+}
+
 #define Pause 1
 #define Start 2
 #define Resume 3