Optimize QGraphicsItem update

[paolom]

Hi, I want to show a video with QGraphicsView and QGraphicsItem.

I need to show every 40 ms a QImage. I use a QTimeLine and a QGraphicsItem.

The problem is that when I call the update() on the QTimeLine slot, there is a lot of time ( about 10 ms ) between the update() call and the paint event of the item.

I know that there isn't an equivalent repaint() for the QGraphicsItem, but anyone know a way to reduce this time ??

Thanks

[wysota]

The time depends on what your application is doing apart showing this one item. Without knowing any details it is not possible to suggest an optimization.

[paolom]

The application is doing anything. I try to use QApplication:rocessEvents() after the update() call but it doesn't change nothing.

Any ideas?

[wysota]

Please show us some code (especially the part where you set the frames on the item). ProcessEvents will not help because the application will be processing events anyway. Also please state where you get the frames from.

[paolom]

This is the code:

/* The QTimeLine slot called every 40 ms */
void VideoItem::goToFrame(int frameNumber)
{
    m_currentFrameNumber = frameNumber;
    updateFrame();
}
 
void VideoItem::updateFrame()
{
    if ( m_file )
    {
        QImage im;
        bool finished;
        if ( ( m_currentFrameNumber - m_previousFrameNumber ) == 1 )
        {
            im = m_file->getNextFrame(finished);
        }
        else
        {
            for ( int i = 0 ; i < ( m_currentFrameNumber - ( m_previousFrameNumber + 1 ) ) ; i++ )
                m_file->getNextFrame(finished,false);
 
            if ( !finished )
                im = m_file->getNextFrame(finished);
 
        }
 
        m_previousFrameNumber = m_currentFrameNumber;
 
        if ( !im.isNull() && !finished)
        {
            m_counter++;
            m_frameCount = m_currentFrameNumber;
 
            setCurrentImage(im);
        }
        else
        {
 
            stop();
 
            emit videoFinished();
       }
    }
}
 
void VideoItem::setCurrentImage(QImage im)
{
    m_currentImage = im;
    update();
}

/* The QTimeLine slot called every 40 ms */
void VideoItem::goToFrame(int frameNumber)
{
    m_currentFrameNumber = frameNumber;
    updateFrame();
}

void VideoItem::updateFrame()
{
    if ( m_file )
    {
        QImage im;
        bool finished;
        if ( ( m_currentFrameNumber - m_previousFrameNumber ) == 1 )
        {
            im = m_file->getNextFrame(finished);
        }
        else
        {
            for ( int i = 0 ; i < ( m_currentFrameNumber - ( m_previousFrameNumber + 1 ) ) ; i++ )
                m_file->getNextFrame(finished,false);

            if ( !finished )
                im = m_file->getNextFrame(finished);

        }

        m_previousFrameNumber = m_currentFrameNumber;

        if ( !im.isNull() && !finished)
        {
            m_counter++;
            m_frameCount = m_currentFrameNumber;

            setCurrentImage(im);
        }
        else
        {

            stop();

            emit videoFinished();
       }
    }
}

void VideoItem::setCurrentImage(QImage im)
{
    m_currentImage = im;
    update();
}

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[wysota]

What is m_file and how does its getNextFrame work? Does it load an image from a file? Also, how large is each frame?