[Interest] double-buffering, quality drop

[Alexander Semke]

> Which Qt version?
> https://bugreports.qt.io/browse/QTBUG-42330
> Is perhaps related?
4.8.5 in openSuse 13.1

Actually, without painter.setRenderHint(QPainter::SmoothPixmapTransform, 
true); the quality is even worser... But I don't really understand why this 
render hint has an effect at all. 

The size of the pixmap is equal to the size of the graphics item 

QPixmap pixmap(boundingRectangle.width(), boundingRectangle.height());

and there is nothing to scale/transform when doing drawPixmap:

painter->drawPixmap(boundingRectangle.topLeft(), m_pixmap);

What  I don't exactly understand yet are the different units used here. The 
size of the graphics item is in scene units, the size of the pixmap is in 
pixels(?). But one pixel is not equal to one scene unit. Why do I get the 
correct size of the curve without doing any scaling in paint()?


-- 
Alexander