void GraphicsContext::setCompositeOperation(CompositeOperator op)
{
    if (paintingDisabled())
        return;

    m_data->p().setCompositionMode(toQtCompositionMode(op));
}
void GraphicsContext::setCompositeOperation(CompositeOperator op)
{
    if (paintingDisabled())
        return;

    if (m_data->p()->paintEngine()->hasFeature(QPaintEngine::PorterDuff))
        m_data->p()->setCompositionMode(toQtCompositionMode(op));
}