Rework how animationsystem interoperate with an animation driver.

We need to keep track of both wall time which are used for pauses
and actual animation driver time which is used for actual animations.
When switching between these, we need to also maintain the temporal
drift potentially introduced by the driver and also the time
that has passed in wall-time from when a pause has started until
an action animation takes over.

This change introduces a well defined elapsed() function in
QUnifiedTimer which will return the right value based on which
mode we are currently in. It also introduces start/stopAnimationDriver
functions which helps us maintain the temporal drift and pause-delta.

Change-Id: I5b5100432a6db444a413d1bca4f2d5f800e8cf3e
Reviewed-by: Michael Brasser <michael.brasser@live.com>

src/corelib/animation/qabstractanimation.cpp

@@ -222,7 +222,8 @@ QUnifiedTimer::QUnifiedTimer() :
     QObject(), defaultDriver(this), lastTick(0), timingInterval(DEFAULT_TIMER_INTERVAL),
     currentAnimationIdx(0), insideTick(false), insideRestart(false), consistentTiming(false), slowMode(false),
     startTimersPending(false), stopTimerPending(false),
-    slowdownFactor(5.0f), profilerCallback(0)
+    slowdownFactor(5.0f), profilerCallback(0),
+    driverStartTime(0), temporalDrift(0)
 {
     time.invalidate();
     driver = &defaultDriver;
@@ -253,18 +254,56 @@ QUnifiedTimer *QUnifiedTimer::instance()
 
 void QUnifiedTimer::maybeUpdateAnimationsToCurrentTime()
 {
-    qint64 elapsed = driver->elapsed();
-    if (elapsed - lastTick > 50)
-        updateAnimationTimers(elapsed);
+    if (elapsed() - lastTick > 50)
+        updateAnimationTimers(-1);
 }
 
-void QUnifiedTimer::updateAnimationTimers(qint64 currentTick)
+qint64 QUnifiedTimer::elapsed() const
+{
+    if (driver->isRunning())
+        return driverStartTime + driver->elapsed();
+    else if (time.isValid())
+        return time.elapsed() + temporalDrift;
+
+    // Reaching here would normally indicate that the function is called
+    // under the wrong circumstances as neither pauses nor actual animations
+    // are running and there should be no need to query for elapsed().
+    return 0;
+}
+
+void QUnifiedTimer::startAnimationDriver()
+{
+    if (driver->isRunning()) {
+        qWarning("QUnifiedTimer::startAnimationDriver: driver is already running...");
+        return;
+    }
+    // Set the start time to the currently elapsed() value before starting.
+    // This means we get the animation system time including the temporal drift
+    // which is what we want.
+    driverStartTime = elapsed();
+    driver->start();
+}
+
+void QUnifiedTimer::stopAnimationDriver()
+{
+    if (!driver->isRunning()) {
+        qWarning("QUnifiedTimer::stopAnimationDriver: driver is not running");
+        return;
+    }
+    // Update temporal drift. Since the driver is running, elapsed() will
+    // return the total animation time in driver-time. Subtract the current
+    // wall time to get the delta.
+    temporalDrift = elapsed() - time.elapsed();
+    driver->stop();
+}
+
+void QUnifiedTimer::updateAnimationTimers(qint64)
 {
     //setCurrentTime can get this called again while we're the for loop. At least with pauseAnimations
     if(insideTick)
         return;
 
-    qint64 totalElapsed = currentTick >= 0 ? currentTick : driver->elapsed();
+    qint64 totalElapsed = elapsed();
 
     // ignore consistentTiming in case the pause timer is active
     qint64 delta = (consistentTiming && !pauseTimer.isActive()) ?
@@ -323,8 +362,7 @@ void QUnifiedTimer::localRestart()
     } else if (!driver->isRunning()) {
         if (pauseTimer.isActive())
             pauseTimer.stop();
-        driver->setStartTime(time.isValid() ? time.elapsed() : 0);
-        driver->start();
+        startAnimationDriver();
     }
 
 }
@@ -345,35 +383,39 @@ void QUnifiedTimer::setTimingInterval(int interval)
 
     if (driver->isRunning() && !pauseTimer.isActive()) {
         //we changed the timing interval
-        driver->stop();
-        driver->setStartTime(time.isValid() ? time.elapsed() : 0);
-        driver->start();
+        stopAnimationDriver();
+        startAnimationDriver();
     }
 }
 
 void QUnifiedTimer::startTimers()
 {
     startTimersPending = false;
+
+    // Initialize the wall clock right away as we need this for
+    // both localRestart and updateAnimationTimers() down below..
+    if (!time.isValid()) {
+        lastTick = 0;
+        time.start();
+        temporalDrift = 0;
+        driverStartTime = 0;
+    }
+
     if (!animationTimers.isEmpty())
         updateAnimationTimers(-1);
 
     //we transfer the waiting animations into the "really running" state
     animationTimers += animationTimersToStart;
     animationTimersToStart.clear();
-    if (!animationTimers.isEmpty()) {
+    if (!animationTimers.isEmpty())
         localRestart();
-        if (!time.isValid()) {
-            lastTick = 0;
-            time.start();
-        }
-    }
 }
 
 void QUnifiedTimer::stopTimer()
 {
     stopTimerPending = false;
     if (animationTimers.isEmpty()) {
-        driver->stop();
+        stopAnimationDriver();
         pauseTimer.stop();
         // invalidate the start reference time
         time.invalidate();
@@ -483,14 +525,12 @@ void QUnifiedTimer::installAnimationDriver(QAnimationDriver *d)
         return;
     }
 
-    if (driver->isRunning()) {
-        driver->stop();
-        d->setStartTime(time.isValid() ? time.elapsed() : 0);
-        d->start();
-    }
-
+    bool running = driver->isRunning();
+    if (running)
+        stopAnimationDriver();
     driver = d;
-
+    if (running)
+        startAnimationDriver();
 }
 
 void QUnifiedTimer::uninstallAnimationDriver(QAnimationDriver *d)
@@ -500,13 +540,12 @@ void QUnifiedTimer::uninstallAnimationDriver(QAnimationDriver *d)
         return;
     }
 
+    bool running = driver->isRunning();
+    if (running)
+        stopAnimationDriver();
     driver = &defaultDriver;
-
-    if (d->isRunning()) {
-        d->stop();
-        driver->setStartTime(time.isValid() ? time.elapsed() : 0);
-        driver->start();
-    }
+    if (running)
+        startAnimationDriver();
 }
 
 /*!
@@ -604,6 +643,7 @@ void QAnimationTimer::restartAnimationTimer()
 void QAnimationTimer::startAnimations()
 {
     startAnimationPending = false;
+
     //force timer to update, which prevents large deltas for our newly added animations
     if (!animations.isEmpty())
         QUnifiedTimer::instance()->maybeUpdateAnimationsToCurrentTime();
@@ -749,20 +789,25 @@ QAnimationDriver::~QAnimationDriver()
     This is to take into account that pauses can occur in running
     animations which will stop the driver, but the time still
     increases.
+
+    \obsolete
+
+    This logic is now handled internally in the animation system.
  */
-void QAnimationDriver::setStartTime(qint64 startTime)
+void QAnimationDriver::setStartTime(qint64)
 {
-    Q_D(QAnimationDriver);
-    d->startTime = startTime;
 }
 
 /*!
     Returns the start time of the animation.
+
+    \obsolete
+
+    This logic is now handled internally in the animation system.
  */
 qint64 QAnimationDriver::startTime() const
 {
-    Q_D(const QAnimationDriver);
-    return d->startTime;
+    return 0;
 }
 
 
@@ -772,6 +817,10 @@ qint64 QAnimationDriver::startTime() const
 
     If \a timeStep is positive, it will be used as the current time in the
     calculations; otherwise, the current clock time will be used.
+
+    Since 5.4, the timeStep argument is ignored and elapsed() will be
+    used instead in combination with the internal time offsets of the
+    animation system.
  */
 
 void QAnimationDriver::advanceAnimation(qint64 timeStep)

src/corelib/animation/qabstractanimation.h

@@ -149,6 +149,7 @@ public:
 
     virtual qint64 elapsed() const;
 
+    // ### Qt6: Remove these two functions
     void setStartTime(qint64 startTime);
     qint64 startTime() const;
 
@@ -157,6 +158,7 @@ Q_SIGNALS:
     void stopped();
 
 protected:
+    // ### Qt6: Remove timestep argument
     void advanceAnimation(qint64 timeStep = -1);
     virtual void start();
     virtual void stop();

src/corelib/animation/qabstractanimation_p.h

@@ -132,9 +132,8 @@ private:
 class Q_CORE_EXPORT QAnimationDriverPrivate : public QObjectPrivate
 {
 public:
-    QAnimationDriverPrivate() : running(false), startTime(0) {}
+    QAnimationDriverPrivate() : running(false) {}
     bool running;
-    qint64 startTime;
 };
 
 class Q_CORE_EXPORT QAbstractAnimationTimer : public QObject
@@ -193,6 +192,10 @@ public:
     int runningAnimationCount();
     void registerProfilerCallback(void (*cb)(qint64));
 
+    void startAnimationDriver();
+    void stopAnimationDriver();
+    qint64 elapsed() const;
+
 protected:
     void timerEvent(QTimerEvent *);
 
@@ -233,6 +236,9 @@ private:
     int closestPausedAnimationTimerTimeToFinish();
 
     void (*profilerCallback)(qint64);
+
+    qint64 driverStartTime; // The time the animation driver was started
+    qint64 temporalDrift; // The delta between animation driver time and wall time.
 };
 
 class QAnimationTimer : public QAbstractAnimationTimer