Which Qt version?
https://bugreports.qt.io/browse/QTBUG-42330
Is perhaps related?
Harri
On 03/02/2015 08:55, Alexander Semke wrote:
Hi,
I'm one of the developers of LabPlot, a KDE-application for interactive
plotting and analysis of data. I'm struggling with a problem since long time
that prevents the next release of the software. So, any help on this issue
will be highly appreciated :-)
To speed up the painting of large curves we use the "double buffering"
technique - the curve is painted on a QPixmap in updatePixmap()-function (only
called when the user changes the properties of the curve) and then painted to
Curve (derived from QGraphicsItem) in the paint()-function (called much more
frequently)
Curve::updatePixmap() {
QPixmap pixmap(boundingRectangle.width(), boundingRectangle.height());
QPainter painter(&pixmap);
painter.setRenderHint(QPainter::Antialiasing, true);
//perform drawing
m_pixmap = pixmap;
}
Curve::paint((QPainter* painter, const QStyleOptionGraphicsItem*, QWidget*) {
painter->save();
painter->setPen(Qt::NoPen);
painter->setBrush(Qt::NoBrush);
painter->setRenderHint(QPainter::SmoothPixmapTransform, true);
painter->drawPixmap(boundingRectangle.topLeft(), m_pixmap);
painter->restore();
}
The performance gain is huge. But there is also a huge drop in the quality
that I cannot explain. I attached two screenshots - with and without double
buffering. Without double buffering just means that all the drawing stuff is
done in paint() directly.
What am I doing here wrong? Any ideas?
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