Wrote this SharedTimeLine thing, then converted the wrong class to use it, oops. Seems to work perfectly, though, so might as well use it.

src/libtomahawk/utils/tomahawkutils.cpp

@@ -609,7 +609,8 @@ removeDirectory( const QString& dir )
 }
 
 
-quint64 infosystemRequestId()
+quint64
+infosystemRequestId()
 {
     QMutexLocker locker( &s_infosystemRequestIdMutex );
     quint64 result = s_infosystemRequestId;
@@ -633,4 +634,42 @@ crash()
     *a = 1;
 }
 
+
+SharedTimeLine::SharedTimeLine()
+    : QObject( 0 )
+    , m_refcount( 0 )
+{
+    m_timeline.setCurveShape( QTimeLine::LinearCurve );
+    m_timeline.setFrameRange( 0, INT_MAX );
+    m_timeline.setDuration( INT_MAX );
+    m_timeline.setUpdateInterval( 40 );
+    connect( &m_timeline, SIGNAL( frameChanged( int ) ), SIGNAL( frameChanged( int ) ) );
+}
+
+void
+SharedTimeLine::connectNotify( const char* signal )
+{
+    if ( signal == QMetaObject::normalizedSignature( SIGNAL( frameChanged( int ) ) ) ) {
+        m_refcount++;
+        if ( m_timeline.state() != QTimeLine::Running )
+            m_timeline.start();
+    }
+}
+
+
+void
+SharedTimeLine::disconnectNotify( const char* signal )
+{
+    if ( signal == QMetaObject::normalizedSignature( SIGNAL( frameChanged( int ) ) ) )
+    {
+        m_refcount--;
+        if ( m_timeline.state() == QTimeLine::Running && m_refcount == 0 )
+        {
+            m_timeline.stop();
+            deleteLater();
+        }
+    }
+}
+
+
 } // ns

src/libtomahawk/utils/tomahawkutils.h

@@ -26,9 +26,9 @@
 #include <QtCore/QThread>
 #include <QtNetwork/QNetworkProxy>
 #include <QtCore/QStringList>
+#include <QTimeLine>
 #include <typedefs.h>
 
-
 #define RESPATH ":/data/"
 
 
@@ -61,6 +61,34 @@ namespace TomahawkUtils
         ScaledCover
     };
 
+
+    class DLLEXPORT SharedTimeLine : public QObject
+    {
+        Q_OBJECT
+        
+    public:
+        SharedTimeLine();
+
+        virtual ~SharedTimeLine() {}
+
+        int currentFrame() { return m_timeline.currentFrame(); }
+
+        void setUpdateInterval( int msec ) { if ( msec != m_timeline.updateInterval() ) m_timeline.setUpdateInterval( msec ); }
+
+    signals:
+        void frameChanged( int );
+
+    protected slots:
+        virtual void connectNotify( const char *signal );
+
+        virtual void disconnectNotify( const char *signal );
+
+    private:
+        int m_refcount;
+        QTimeLine m_timeline;
+    };
+    
+
     class DLLEXPORT NetworkProxyFactory : public QNetworkProxyFactory
     {
     public:
@@ -86,6 +114,7 @@ namespace TomahawkUtils
         QNetworkProxy m_proxy;
     };
     
+
     DLLEXPORT QString appFriendlyVersion();
 
     DLLEXPORT QDir appConfigDir();

src/libtomahawk/widgets/FadingPixmap.cpp

@@ -18,22 +18,33 @@
 
 #include "FadingPixmap.h"
 
+#include "utils/logger.h"
+
+#include <QTimer>
+#include <QBuffer>
 #include <QPainter>
 
 #define ANIMATION_TIME 1000
 
+QWeakPointer< TomahawkUtils::SharedTimeLine > FadingPixmap::s_stlInstance = QWeakPointer< TomahawkUtils::SharedTimeLine >();
+
+QWeakPointer< TomahawkUtils::SharedTimeLine >
+FadingPixmap::stlInstance()
+{
+    if ( s_stlInstance.isNull() )
+        s_stlInstance = QWeakPointer< TomahawkUtils::SharedTimeLine> ( new TomahawkUtils::SharedTimeLine() );
+
+    return s_stlInstance;
+}
+
+
 FadingPixmap::FadingPixmap( QWidget* parent )
     : QLabel( parent )
+    , m_oldPixmap( QPixmap() )
     , m_fadePct( 100 )
+    , m_startFrame( 0 )
 {
 //    setCursor( Qt::PointingHandCursor );
-
-    m_timeLine = new QTimeLine( ANIMATION_TIME, this );
-    m_timeLine->setUpdateInterval( 20 );
-    m_timeLine->setEasingCurve( QEasingCurve::Linear );
-
-    connect( m_timeLine, SIGNAL( frameChanged( int ) ), SLOT( onAnimationStep( int ) ) );
-    connect( m_timeLine, SIGNAL( finished() ), SLOT( onAnimationFinished() ) );
 }
 
 
@@ -45,8 +56,14 @@ FadingPixmap::~FadingPixmap()
 void
 FadingPixmap::onAnimationStep( int frame )
 {
-    m_fadePct = (float)frame / 10.0;
+    m_fadePct = (float)( frame - m_startFrame ) / 10.0;
+    if ( m_fadePct > 100.0 )
+        m_fadePct = 100.0;
+    
     repaint();
+
+    if ( m_fadePct == 100.0 )
+        QTimer::singleShot( 0, this, SLOT( onAnimationFinished() ) );
 }
 
 
@@ -60,13 +77,25 @@ FadingPixmap::onAnimationFinished()
     {
         setPixmap( m_pixmapQueue.takeFirst() );
     }
+
+    disconnect( stlInstance().data(), SIGNAL( frameChanged( int ) ), this, SLOT( onAnimationStep( int ) ) );
 }
 
 
 void
 FadingPixmap::setPixmap( const QPixmap& pixmap, bool clearQueue )
 {
-    if ( m_timeLine->state() == QTimeLine::Running )
+    QByteArray ba;
+    QBuffer buffer( &ba );
+    buffer.open( QIODevice::WriteOnly );
+    pixmap.save( &buffer, "PNG" );
+    QString newImageMd5 = TomahawkUtils::md5( buffer.data() );
+    if ( m_oldImageMd5 == newImageMd5 )
+        return;
+
+    m_oldImageMd5 = newImageMd5;
+
+    if ( !m_oldPixmap.isNull() )
     {
         if ( clearQueue )
             m_pixmapQueue.clear();
@@ -78,9 +107,10 @@ FadingPixmap::setPixmap( const QPixmap& pixmap, bool clearQueue )
     m_oldPixmap = m_pixmap;
     m_pixmap = pixmap;
 
-    m_timeLine->setFrameRange( 0, 1000 );
+    stlInstance().data()->setUpdateInterval( 20 );
-    m_timeLine->setDirection( QTimeLine::Forward );
+    m_startFrame = stlInstance().data()->currentFrame();
-    m_timeLine->start();
+    m_fadePct = 0;
+    connect( stlInstance().data(), SIGNAL( frameChanged( int ) ), this, SLOT( onAnimationStep( int ) ) );
 }
 
 

src/libtomahawk/widgets/FadingPixmap.h

@@ -19,9 +19,12 @@
 #ifndef FADINGPIXMAP_H
 #define FADINGPIXMAP_H
 
+#include "utils/tomahawkutils.h"
+
 #include <QLabel>
 #include <QPaintEvent>
 #include <QTimeLine>
+#include <QWeakPointer>
 
 #include "dllmacro.h"
 
@@ -33,12 +36,15 @@ class DLLEXPORT FadingPixmap : public QLabel
 {
 Q_OBJECT
 
+    static QWeakPointer< TomahawkUtils::SharedTimeLine > stlInstance();
+
 public:
     FadingPixmap( QWidget* parent = 0 );
     virtual ~FadingPixmap();
 
 public slots:
     virtual void setPixmap( const QPixmap& pixmap, bool clearQueue = true );
+    void onAnimationStep( int frame );
 
 signals:
     void clicked();
@@ -48,17 +54,21 @@ protected:
     void mouseReleaseEvent( QMouseEvent* event );
 
 private slots:
-    void onAnimationStep( int frame );
     void onAnimationFinished();
 
 private:
     QPixmap m_pixmap;
     QPixmap m_oldPixmap;
 
+    QString m_oldImageMd5;
+    
     QList<QPixmap> m_pixmapQueue;
     
-    QTimeLine* m_timeLine;
     int m_fadePct;
+
+    int m_startFrame;
+
+    static QWeakPointer< TomahawkUtils::SharedTimeLine > s_stlInstance;
 };
 
 #endif