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Tablet example: paint only the changed areas of the canvas 

This improves performance significantly.

Change-Id: I9a8782148ce03a2bc85759c4e8c1eecb37467cf6
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
bb10
Shawn Rutledge 2017-09-14 15:14:32 +02:00
parent 09f59271e6
commit d2c05b0c85
1 changed files with 4 additions and 2 deletions
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6
examples/widgets/widgets/tablet/tabletcanvas.cpp
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@ -148,12 +148,14 @@ void TabletCanvas::initPixmap()
m_pixmap = newPixmap;
}
void TabletCanvas::paintEvent(QPaintEvent *)
void TabletCanvas::paintEvent(QPaintEvent *event)
{
if (m_pixmap.isNull())
initPixmap();
QPainter painter(this);
painter.drawPixmap(0, 0, m_pixmap);
QRect pixmapPortion = QRect(event->rect().topLeft() * devicePixelRatioF(),
event->rect().size() * devicePixelRatioF());
painter.drawPixmap(event->rect().topLeft(), m_pixmap, pixmapPortion);
}
//! [4]