Make QPropertyAnimation symetric wrt direction

It is now possible to set a start value and no end value and starting
the animation will pick the default end value from the current value
of the property that's being animated.

3 files changed, 81 insertions, 39 deletions

diff --git a/src/corelib/animation/qvariantanimation.cpp b/src/corelib/animation/qvariantanimation.cpp
index 61321c8..04e0980 100644
--- a/src/corelib/animation/qvariantanimation.cpp
+++ b/src/corelib/animation/qvariantanimation.cpp
@@ -178,8 +178,7 @@ template<> Q_INLINE_TEMPLATE QLineF _q_interpolate(const QLineF &f, const QLineF
     return QLineF( _q_interpolate(f.p1(), t.p1(), progress), _q_interpolate(f.p2(), t.p2(), progress));
 }
 
-QVariantAnimationPrivate::QVariantAnimationPrivate() : duration(250), hasStartValue(false),
-                          interpolator(&defaultInterpolator),
+QVariantAnimationPrivate::QVariantAnimationPrivate() : duration(250), interpolator(&defaultInterpolator),
                           changedSignalMask(1 << QVariantAnimation::staticMetaObject.indexOfSignal("valueChanged(QVariant)"))
 {
     //we keep the mask so that we emit valueChanged only when needed (for performance reasons)
@@ -222,34 +221,52 @@ void QVariantAnimationPrivate::updateInterpolator()
 void QVariantAnimationPrivate::recalculateCurrentInterval(bool force/*=false*/)
 {
     // can't interpolate if we have only 1 key value
-    if (keyValues.count() <= 1)
+    if ((keyValues.count() + (defaultStartValue.isValid() ? 1 : 0)) <=1)
         return;
 
     const qreal progress = easing.valueForProgress(((duration == 0) ? qreal(1) : qreal(currentTime) / qreal(duration)));
 
     if (force || progress < currentInterval.start.first || progress > currentInterval.end.first) {
         //let's update currentInterval
-        QVariantAnimation::KeyValues::const_iterator itStart = qLowerBound(keyValues.constBegin(),
+        QVariantAnimation::KeyValues::const_iterator it = qLowerBound(keyValues.constBegin(),
                                                                            keyValues.constEnd(),
                                                                            qMakePair(progress, QVariant()),
                                                                            animationValueLessThan);
-        QVariantAnimation::KeyValues::const_iterator itEnd = itStart;
-
-        // If we are at the end we should continue to use the last keyValues in case of extrapolation (progress > 1.0).
-        // This is because the easing function can return a value slightly outside the range [0, 1]
-        if (itStart != keyValues.constEnd()) {
-            // this can't happen because we always prepend the default start value there
-            if (itStart == keyValues.constBegin()) {
-                ++itEnd;
+        if (it == keyValues.constEnd()) {
+            if (direction == QVariantAnimation::Backward && defaultStartValue.isValid()) {
+                --it;
+                if (it->first == 1) {
+                    //we have an end value (item with progress = 1)
+                    currentInterval.start = *(it-1);
+                    currentInterval.end = *it;
+                } else if (direction == QVariantAnimation::Backward && defaultStartValue.isValid()) {
+                    //the default start value should be used as the default end value
+                    currentInterval.start = *it;
+                    currentInterval.end = qMakePair(qreal(1), defaultStartValue);
+                } else {
+                    ///This should not happen
+                }
+            }
+        } else if (it == keyValues.constBegin()) {
+            if (it->first == progress || it->first == 0) {
+                //the item pointed to by it is the start element in the range
+                //we also test if the current element is for progress 0 (ie the real start) because
+                //some easing curves might get the progress below 0.
+                currentInterval.start = *it;
+                currentInterval.end = *(it+1);
+            } else if (direction == QVariantAnimation::Forward && defaultStartValue.isValid()) {
+                currentInterval.start = qMakePair(qreal(0), defaultStartValue);
+                currentInterval.end = *it;
             } else {
-                --itStart;
+                ///this should not happen
             }
-
-            // update all the values of the currentInterval
-            currentInterval.start = *itStart;
-            currentInterval.end = *itEnd;
-            updateInterpolator();
+        } else {
+            currentInterval.start = *(it-1);
+            currentInterval.end = *it;
         }
+
+        // update all the values of the currentInterval
+        updateInterpolator();
     }
     setCurrentValueForProgress(progress);
 }
@@ -298,8 +315,6 @@ void QVariantAnimationPrivate::setValueAt(qreal step, const QVariant &value)
     } else {
         if (value.isValid())
             result->second = value; // replaces the previous value
-        else if (step == 0 && !hasStartValue && defaultStartValue.isValid())
-            result->second = defaultStartValue; // resets to the default start value
         else
             keyValues.erase(result); // removes the previous value
     }
@@ -310,8 +325,7 @@ void QVariantAnimationPrivate::setValueAt(qreal step, const QVariant &value)
 void QVariantAnimationPrivate::setDefaultStartValue(const QVariant &value)
 {
     defaultStartValue = value;
-    if (!hasStartValue)
-      setValueAt(0, value);
+    recalculateCurrentInterval(/*force=*/true);
 }
 
 /*!
@@ -526,11 +540,7 @@ void QVariantAnimation::setEndValue(const QVariant &value)
 */
 QVariant QVariantAnimation::keyValueAt(qreal step) const
 {
-    Q_D(const QVariantAnimation);
-    if (step == 0 && !d->hasStartValue)
-        return QVariant(); //special case where we don't have an explicit startValue
-
-    return d->valueAt(step);
+    return d_func()->valueAt(step);
 }
 
 /*!
@@ -552,10 +562,7 @@ QVariant QVariantAnimation::keyValueAt(qreal step) const
 */
 void QVariantAnimation::setKeyValueAt(qreal step, const QVariant &value)
 {
-    Q_D(QVariantAnimation);
-    if (step == 0)
-        d->hasStartValue = value.isValid();
-    d->setValueAt(step, value);
+    d_func()->setValueAt(step, value);
 }
 
 /*!
@@ -565,12 +572,7 @@ void QVariantAnimation::setKeyValueAt(qreal step, const QVariant &value)
 */
 QVariantAnimation::KeyValues QVariantAnimation::keyValues() const
 {
-    Q_D(const QVariantAnimation);
-    QVariantAnimation::KeyValues ret = d->keyValues;
-    //in case we added the default start value, we remove it
-    if (!d->hasStartValue && !ret.isEmpty() && ret.at(0).first == 0)
-        ret.remove(0);
-    return ret;
+    return d_func()->keyValues;
 }
 
 /*!
@@ -584,7 +586,6 @@ void QVariantAnimation::setKeyValues(const KeyValues &keyValues)
     Q_D(QVariantAnimation);
     d->keyValues = keyValues;
     qSort(d->keyValues.begin(), d->keyValues.end(), animationValueLessThan);
-    d->hasStartValue = !d->keyValues.isEmpty() && d->keyValues.at(0).first == 0;
     d->recalculateCurrentInterval(/*force=*/true);
 }
 
diff --git a/src/corelib/animation/qvariantanimation_p.h b/src/corelib/animation/qvariantanimation_p.h
index dbfd956..9c9d25b 100644
--- a/src/corelib/animation/qvariantanimation_p.h
+++ b/src/corelib/animation/qvariantanimation_p.h
@@ -84,7 +84,6 @@ public:
     QVariantAnimation::KeyValues keyValues;
     QVariant currentValue;
     QVariant defaultStartValue;
-    bool hasStartValue;
 
     //this is used to keep track of the KeyValue interval in which we currently are
     struct
diff --git a/tests/auto/qpropertyanimation/tst_qpropertyanimation.cpp b/tests/auto/qpropertyanimation/tst_qpropertyanimation.cpp
index 6f49d8e..5af6f39 100644
--- a/tests/auto/qpropertyanimation/tst_qpropertyanimation.cpp
+++ b/tests/auto/qpropertyanimation/tst_qpropertyanimation.cpp
@@ -102,6 +102,7 @@ private slots:
     void easingcurve_data();
     void easingcurve();
     void startWithoutStartValue();
+    void startBackwardWithoutEndValue();
     void playForwardBackward();
     void interpolated();
     void setStartEndValues_data();
@@ -582,6 +583,47 @@ void tst_QPropertyAnimation::startWithoutStartValue()
     QVERIFY(current <= 110);
 }
 
+void tst_QPropertyAnimation::startBackwardWithoutEndValue()
+{
+    QObject o;
+    o.setProperty("ole", 42);
+    QCOMPARE(o.property("ole").toInt(), 42);
+
+    QPropertyAnimation anim(&o, "ole");
+    anim.setStartValue(100);
+    anim.setDirection(QAbstractAnimation::Backward);
+
+    //we start without an end value
+    anim.start();
+    QCOMPARE(anim.state(), QAbstractAnimation::Running);
+    QCOMPARE(o.property("ole").toInt(), 42); //the initial value
+
+    QTest::qWait(100);
+    int current = anim.currentValue().toInt();
+    //it is somewhere in the animation
+    QVERIFY(current > 42);
+    QVERIFY(current < 100);
+
+    QTest::qWait(200);
+    QCOMPARE(anim.state(), QVariantAnimation::Stopped);
+    current = anim.currentValue().toInt();
+    QCOMPARE(current, 100);
+    QCOMPARE(o.property("ole").toInt(), current);
+
+    anim.setStartValue(110);
+    anim.start();
+    current = anim.currentValue().toInt();
+    // the default start value will reevaluate the current property
+    // and set it to the end value of the last iteration
+    QCOMPARE(current, 100);
+    QTest::qWait(100);
+    current = anim.currentValue().toInt();
+    //it is somewhere in the animation
+    QVERIFY(current >= 100);
+    QVERIFY(current <= 110);
+}
+
+
 void tst_QPropertyAnimation::playForwardBackward()
 {
     QObject o;