QPixmap::grabWindow too slow

[niko]

Hello,

I have a widget, that makes a screenshot every second and paints it out:

ZoomWidget::ZoomWidget(QWidget* parent) : QWidget(parent)
{
    QTimer *timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(update()));
    timer->start(1000);
}
 
void ZoomWidget::paintEvent(QPaintEvent * /*event*/) {
    QPainter painter(this);
    painter.drawPixmap(0, 0, QPixmap::grabWindow(QApplication::desktop()->winId()), 0, 0, 100, 100);
 
}

ZoomWidget::ZoomWidget(QWidget* parent) : QWidget(parent)
{
    QTimer *timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(update()));
    timer->start(1000);
}

void ZoomWidget::paintEvent(QPaintEvent * /*event*/) {
    QPainter painter(this);
    painter.drawPixmap(0, 0, QPixmap::grabWindow(QApplication::desktop()->winId()), 0, 0, 100, 100);

}

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it works, but slows down my system quite a lot (every second a small lag)

if i change the interval to 1ms, X has 100% percent processor-load.

how could i speed up this?

(i took a look at kmag - which does basically the same thing in qt3 and is much faster - not really fast either - but still better)

niko

[wysota]

Get a snapshot only when you need it. It is very expensive to grab the desktop widget.

[niko]

thanks, that helped a lot!
(i could have thought about that myselfe...)

niko