From 8738f09b9fc1b35e3dc78211368d87069f3071f7 Mon Sep 17 00:00:00 2001
From: J-P Nurmi <jpnurmi@digia.com>
Date: Sat, 26 Jul 2014 17:29:54 +0200
Subject: Reduce the default frame rate of style animations

Halves the amount of paint events triggered by transient scrollbars.

Task-number: QTBUG-30316
Change-Id: Ifdf968d5c45013332758a6b751ce11d1ef2a2ca8
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
---
 src/widgets/styles/qcommonstyle.cpp    |  2 +-
 src/widgets/styles/qstyleanimation.cpp | 25 ++++++++++++++++++++++---
 src/widgets/styles/qstyleanimation_p.h | 15 +++++++++++++++
 3 files changed, 38 insertions(+), 4 deletions(-)

(limited to 'src/widgets/styles')

diff --git a/src/widgets/styles/qcommonstyle.cpp b/src/widgets/styles/qcommonstyle.cpp
index 94498f48c9..d8b67edff8 100644
--- a/src/widgets/styles/qcommonstyle.cpp
+++ b/src/widgets/styles/qcommonstyle.cpp
@@ -1155,7 +1155,7 @@ void QCommonStylePrivate::startAnimation(QStyleAnimation *animation) const
     stopAnimation(animation->target());
     q->connect(animation, SIGNAL(destroyed()), SLOT(_q_removeAnimation()), Qt::UniqueConnection);
     animations.insert(animation->target(), animation);
-    animation->start(QAbstractAnimation::DeleteWhenStopped);
+    animation->start();
 }
 
 /*! \internal */
diff --git a/src/widgets/styles/qstyleanimation.cpp b/src/widgets/styles/qstyleanimation.cpp
index 85dc357ab5..e6e47a98e9 100644
--- a/src/widgets/styles/qstyleanimation.cpp
+++ b/src/widgets/styles/qstyleanimation.cpp
@@ -50,7 +50,7 @@ static const qreal ScrollBarFadeOutDuration = 200.0;
 static const qreal ScrollBarFadeOutDelay = 450.0;
 
 QStyleAnimation::QStyleAnimation(QObject *target) : QAbstractAnimation(target),
-    _delay(0), _duration(-1), _startTime(QTime::currentTime())
+    _delay(0), _duration(-1), _startTime(QTime::currentTime()), _fps(ThirtyFps), _skip(0)
 {
 }
 
@@ -93,6 +93,16 @@ void QStyleAnimation::setStartTime(const QTime &time)
     _startTime = time;
 }
 
+QStyleAnimation::FrameRate QStyleAnimation::frameRate() const
+{
+    return _fps;
+}
+
+void QStyleAnimation::setFrameRate(FrameRate fps)
+{
+    _fps = fps;
+}
+
 void QStyleAnimation::updateTarget()
 {
     QEvent event(QEvent::StyleAnimationUpdate);
@@ -102,6 +112,12 @@ void QStyleAnimation::updateTarget()
         stop();
 }
 
+void QStyleAnimation::start()
+{
+    _skip = 0;
+    QAbstractAnimation::start(DeleteWhenStopped);
+}
+
 bool QStyleAnimation::isUpdateNeeded() const
 {
     return currentTime() > _delay;
@@ -109,8 +125,11 @@ bool QStyleAnimation::isUpdateNeeded() const
 
 void QStyleAnimation::updateCurrentTime(int)
 {
-    if (target() && isUpdateNeeded())
-        updateTarget();
+    if (++_skip >= _fps) {
+        _skip = 0;
+        if (target() && isUpdateNeeded())
+            updateTarget();
+    }
 }
 
 QProgressStyleAnimation::QProgressStyleAnimation(int speed, QObject *target) :
diff --git a/src/widgets/styles/qstyleanimation_p.h b/src/widgets/styles/qstyleanimation_p.h
index c344858812..19e629cb25 100644
--- a/src/widgets/styles/qstyleanimation_p.h
+++ b/src/widgets/styles/qstyleanimation_p.h
@@ -78,8 +78,21 @@ public:
     QTime startTime() const;
     void setStartTime(const QTime &time);
 
+    enum FrameRate {
+        DefaultFps,
+        SixtyFps,
+        ThirtyFps,
+        TwentyFps
+    };
+
+    FrameRate frameRate() const;
+    void setFrameRate(FrameRate fps);
+
     void updateTarget();
 
+public Q_SLOTS:
+    void start();
+
 protected:
     virtual bool isUpdateNeeded() const;
     virtual void updateCurrentTime(int time);
@@ -88,6 +101,8 @@ private:
     int _delay;
     int _duration;
     QTime _startTime;
+    FrameRate _fps;
+    int _skip;
 };
 
 class QProgressStyleAnimation : public QStyleAnimation
-- 
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