What is the best way to display an animated icon i

Question

I've been struggling with this for some times now, and I can't seem to find the right way to do this.

What I would like is the ability to use an animated icon as a decoration for some of my items (typically to show that some processing is occuring for this particular item). I have a custom table model, that I display in a QTableView.

My first idea was to create a custom delegate that would take care of displaying the animation. When passed a QMovie for the decoration role, the delegate would connect to the QMovie in order to update the display every time a new frame is available (see code below). However, the painter does not seem to remain valid after the call to the delegate's paint method (I get an error when calling the painter's save method, probably because the pointer no longer points to valid memory).

Another solution would be to emit the dataChanged signal of the item every time a new frame is available, but 1) that would induce many unnecessary overhead, since the data is not really changed; 2) it does not seem really clean to handle the movie at the model level: it should be the responsibility of the display tier (QTableView or the delegate) to handle the display of new frames.

Does anyone know a clean (and preferably efficient) way to display animation in Qt views?

---

For those interested, here is the code of the delegate I developped (which does not work at the moment).

// Class that paints movie frames every time they change, using the painter
// and style options provided
class MoviePainter : public QObject
{
    Q_OBJECT

  public: // member functions
    MoviePainter( QMovie * movie, 
                  QPainter * painter, 
                  const QStyleOptionViewItem & option );

  public slots:
    void paint( ) const;

  private: // member variables
    QMovie               * movie_;
    QPainter             * painter_;
    QStyleOptionViewItem   option_;
};


MoviePainter::MoviePainter( QMovie * movie,
                            QPainter * painter,
                            const QStyleOptionViewItem & option )
  : movie_( movie ), painter_( painter ), option_( option )
{
    connect( movie, SIGNAL( frameChanged( int ) ),
             this,  SLOT( paint( ) ) );
}

void MoviePainter::paint( ) const
{
    const QPixmap & pixmap = movie_->currentPixmap();

    painter_->save();
    painter_->drawPixmap( option_.rect, pixmap );
    painter_->restore();
}

//-------------------------------------------------

//Custom delegate for handling animated decorations.
class MovieDelegate : public QStyledItemDelegate
{
    Q_OBJECT

  public: // member functions
    MovieDelegate( QObject * parent = 0 );
    ~MovieDelegate( );

    void paint( QPainter * painter, 
                const QStyleOptionViewItem & option, 
                const QModelIndex & index ) const;

  private: // member functions
    QMovie * qVariantToPointerToQMovie( const QVariant & variant ) const;

  private: // member variables
    mutable std::map< QModelIndex, detail::MoviePainter * > map_;
};

MovieDelegate::MovieDelegate( QObject * parent )
  : QStyledItemDelegate( parent )
{
}

MovieDelegate::~MovieDelegate( )
{
    typedef  std::map< QModelIndex, detail::MoviePainter * > mapType;

          mapType::iterator it = map_.begin();
    const mapType::iterator end = map_.end();

    for ( ; it != end ; ++it )
    {
        delete it->second;
    }
}

void MovieDelegate::paint( QPainter * painter, 
                           const QStyleOptionViewItem & option, 
                           const QModelIndex & index ) const
{
    QStyledItemDelegate::paint( painter, option, index );

    const QVariant & data = index.data( Qt::DecorationRole );

    QMovie * movie = qVariantToPointerToQMovie( data );

    // Search index in map
    typedef std::map< QModelIndex, detail::MoviePainter * > mapType;

    mapType::iterator it = map_.find( index );

    // if the variant is not a movie
    if ( ! movie )
    {
        // remove index from the map (if needed)
        if ( it != map_.end() )
        {
            delete it->second;
            map_.erase( it );
        }

        return;
    }

    // create new painter for the given index (if needed)
    if ( it == map_.end() )
    {
        map_.insert( mapType::value_type( 
                index, new detail::MoviePainter( movie, painter, option ) ) );
    }
}

QMovie * MovieDelegate::qVariantToPointerToQMovie( const QVariant & variant ) const
{
    if ( ! variant.canConvert< QMovie * >() ) return NULL;

    return variant.value< QMovie * >();
}

Answer 1

For the record, I ended up using QAbstractItemView::setIndexWidget from inside the paint method of my delegate, to insert a QLabel displaying the QMovie inside the item (see code below).

This solution works quite nicely, and keep the display issues separated from the model. One drawback is that the display of a new frame in the label causes the entire item to be rendered again, resulting in almost continuous calls to the delegate's paint method...

To reduce the overhead inccured by these calls, I tried to minimize the work done for handling movies in the delegate by reusing the existing label if there is one. However, this results in weird behavior when resizing the windows: the animation gets shifted to the right, as if two labels were positioned side by side.

So well, here is a possible solution, feel free to comment on ways to improve it!

// Declaration

#ifndef MOVIEDELEGATE_HPP
#define MOVIEDELEGATE_HPP

#include <QtCore/QModelIndex>
#include <QtGui/QStyledItemDelegate>


class QAbstractItemView;
class QMovie;


class MovieDelegate : public QStyledItemDelegate
{
    Q_OBJECT

  public: // member functions

    MovieDelegate( QAbstractItemView & view, QObject * parent = NULL );

    void paint( QPainter * painter, 
                const QStyleOptionViewItem & option, 
                const QModelIndex & index ) const;


  private: // member functions

    QMovie * qVariantToPointerToQMovie( const QVariant & variant ) const;


  private: // member variables

    mutable QAbstractItemView & view_;
};

#endif // MOVIEDELEGATE_HPP


// Definition

#include "movieDelegate.hpp"

#include <QtCore/QVariant>
#include <QtGui/QAbstractItemView>
#include <QtGui/QLabel>
#include <QtGui/QMovie>


Q_DECLARE_METATYPE( QMovie * )


//---------------------------------------------------------
// Public member functions
//---------------------------------------------------------

MovieDelegate::MovieDelegate( QAbstractItemView & view, QObject * parent )
  : QStyledItemDelegate( parent ), view_( view )
{
}


void MovieDelegate::paint( QPainter * painter, 
                           const QStyleOptionViewItem & option, 
                           const QModelIndex & index ) const
{
    QStyledItemDelegate::paint( painter, option, index );

    const QVariant & data = index.data( Qt::DecorationRole );

    QMovie * movie = qVariantToPointerToQMovie( data );

    if ( ! movie )
    {
        view_.setIndexWidget( index, NULL );
    }
    else
    {
        QObject * indexWidget = view_.indexWidget( index );
        QLabel  * movieLabel  = qobject_cast< QLabel * >( indexWidget );

        if ( movieLabel )
        {
            // Reuse existing label

            if ( movieLabel->movie() != movie )
            {
                movieLabel->setMovie( movie );
            }
        }
        else
        {
            // Create new label;

            movieLabel = new QLabel;

            movieLabel->setMovie( movie );

            view_.setIndexWidget( index, movieLabel );
        }
    }
}


//---------------------------------------------------------
// Private member functions
//---------------------------------------------------------

QMovie * MovieDelegate::qVariantToPointerToQMovie( const QVariant & variant ) const
{
    if ( ! variant.canConvert< QMovie * >() ) return NULL;

    return variant.value< QMovie * >();
}