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c++qtqpainterqpixmapqlabel

QPainter or QLabel is less costly to draw QPixmap

I have to create an Icon pixmap, two methods I am familiarized to do that, One is setting the pixmap as o QLabel and display it, and other is drawing pixmap using QPainter, ie

Method one

Icon::Icon
{
    QLabel iconLab = new QLabel;
    QLabel iconName = new QLabel;
    iconLab->setPixmap("mypixmap.png"); 
    iconName->setText("myiconname");
    QVBoxLayout *iconLayout = new QVBoxLayout; 
    iconLayout->setMargin(0);
    iconLayout->addWidget(iconLab, 1, Qt::AlignCenter);
    iconLayout->addWidget(iconName, 1, Qt::AlignCenter);
    iconLayout->setSpacing(0);

    setLayout(iconLayout);
    setMaximumSize(100,160);
    setMinimumSize(100,160);
}

Method 2,

Icon::Icon
{     
    setMaximumSize(100,160);
    setMinimumSize(100,160);
}
Icon::paintEvent(QPaintEvent*)
{      
    QPainter painter;
    painter.drawPixmap(0,0,myPixmap);
    painter.drawText(0,100,myText)
}

I have to draw number of Icons, more than 100, so which one is effective, Thanks in advance,

Solution

  • From a theoretical perspective, the QPainter approach will be faster because the overhead introduced by QLabel is avoided. Internally QLabel needs to use a QPainter as well (using drawPicture()).

    However, it is questionable if this difference will make your application more responsive. I doubt that this optimization will even be noticeable.

    I would recommend to take care of code readability in the first place and take what is easier / feels better to use.

    Once you have the functionality in place and there is a performance problem, you can start profiling and decide where the time and effort to optimize is best invested.