Add prettier drag pixmap.

Still needs to be added to PlaylistModel---potentially refactored out into somewhere shared.
Also, only allow once column in the source model to be dragged, so we get the right amount of drag items.

resources.qrc

@@ -67,5 +67,8 @@
 <file>./data/icons/tomahawk-icon-128.png</file>
 <file>./data/icons/tomahawk-icon-256.png</file>
 <file>./data/icons/tomahawk-icon-512.png</file>
+<file>./data/icons/audio-x-generic-22.png</file>
+<file>./data/icons/audio-x-generic-32.png</file>
+<file>./data/icons/audio-x-generic-16.png</file>
 </qresource>
 </RCC>

src/playlist/collectionview.cpp

@@ -219,6 +219,36 @@ CollectionView::keyPressEvent( QKeyEvent* event )
     }
 }
 
+void 
+CollectionView::startDrag( Qt::DropActions supportedActions )
+{
+    QModelIndexList indexes = selectedIndexes();
+    qDebug() << "Dragging" << indexes.count() << "indexes";
+    for( int i = indexes.count() - 1 ; i >= 0; --i ) {
+        if( !( m_proxyModel->flags( indexes.at( i ) ) & Qt::ItemIsDragEnabled ) )
+            indexes.removeAt(i);
+    }
+    
+    if( indexes.count() == 0 )
+        return;
+    
+    qDebug() << "Dragging" << indexes.count() << "indexes";
+    
+    QMimeData *data = m_proxyModel->mimeData( indexes );
+    if (!data)
+        return;
+    
+    QDrag *drag = new QDrag( this );
+    drag->setMimeData( data );
+    const QPixmap p = createDragPixmap( indexes.count() );
+    drag->setPixmap( p );
+    drag->setHotSpot( QPoint( -20, -20 ) );
+    
+    // NOTE: if we support moving items in the model
+    //       in the future, if exec() returns Qt::MoveAction
+    //       we need to clean up ourselves.
+    drag->exec( supportedActions, Qt::CopyAction );
+}
 
 void
 CollectionView::dragEnterEvent( QDragEnterEvent* event )
@@ -331,3 +361,56 @@ CollectionView::onFilterChanged( const QString& )
     if ( selectedIndexes().count() )
         scrollTo( selectedIndexes().at( 0 ), QAbstractItemView::PositionAtCenter );
 }
+
+// Inspired from dolphin's draganddrophelper.cpp
+QPixmap 
+CollectionView::createDragPixmap( int itemCount ) const
+{
+    // If more than one item is dragged, align the items inside a
+    // rectangular grid. The maximum grid size is limited to 5 x 5 items.
+    int xCount = 3;
+    int size = 32;
+    if ( itemCount > 16 ) {
+        xCount = 5;
+        size = 16;
+    } else if( itemCount > 9 ) {
+        xCount = 4;
+        size = 22;
+    }
+    
+    if( itemCount < xCount ) {
+        xCount = itemCount;
+    }
+    
+    int yCount = itemCount / xCount;
+    if( itemCount % xCount != 0 ) {
+        ++yCount;
+    }
+    if( yCount > xCount ) {
+        yCount = xCount;
+    }
+    // Draw the selected items into the grid cells    
+    QPixmap dragPixmap( xCount * size + xCount - 1, yCount * size + yCount - 1 );
+    dragPixmap.fill( Qt::transparent );
+    
+    QPainter painter(&dragPixmap);
+    painter.setRenderHint( QPainter::Antialiasing );
+    int x = 0;
+    int y = 0;
+    for( int i = 0; i < itemCount; ++i ) {
+        const QPixmap pixmap = QPixmap( QString( ":/data/icons/audio-x-generic-%2.png" ).arg( size ) );
+        painter.drawPixmap(x, y, pixmap);
+        
+        x += size + 1;
+        if (x >= dragPixmap.width()) {
+            x = 0;
+            y += size + 1;
+        }
+        if (y >= dragPixmap.height()) {
+            break;
+        }
+    }
+    
+    return dragPixmap;
+}
+

src/playlist/collectionview.h

@@ -32,7 +32,8 @@ public:
 protected:
     virtual void resizeEvent( QResizeEvent* event );
     virtual void keyPressEvent( QKeyEvent* event );
-
+    
+    virtual void startDrag( Qt::DropActions supportedActions );
     virtual void dragEnterEvent( QDragEnterEvent* event );
     virtual void dragLeaveEvent( QDragLeaveEvent* event ) { m_dragging = false; setDirtyRegion( m_dropRect ); }
     virtual void dragMoveEvent( QDragMoveEvent* event );
@@ -52,6 +53,7 @@ private slots:
 private:
     void restoreColumnsState();
     void saveColumnsState();
+    QPixmap createDragPixmap( int itemCount ) const;
 
     TrackModel* m_model;
     PlaylistInterface* m_modelInterface;

src/playlist/trackmodel.cpp

@@ -127,7 +127,7 @@ TrackModel::flags( const QModelIndex& index ) const
 {
     Qt::ItemFlags defaultFlags = QAbstractItemModel::flags( index );
 
-    if ( index.isValid() )
+    if ( index.isValid() && index.column() == 0 )
         return Qt::ItemIsDragEnabled | Qt::ItemIsDropEnabled | defaultFlags;
     else
         return Qt::ItemIsDropEnabled | defaultFlags;