Den 8 dec. 2016 1:02 fm skrev "Ch'Gans" <chg...@gna.org>: > > Hi, > > The documentation of QPainterPathStroker's curve threshold says: > ---------------------------------------------------------------- > Specifies the curve flattening threshold, controlling the granularity > with which the generated outlines' curve is drawn. > > The default threshold is a well adjusted value (0.25), and normally > you should not need to modify it. However, you can make the curve's > appearance smoother by decreasing its value. > ---------------------------------------------------------------- > > However i have noticed that when used in a graphics scene with objects > of small size, the default threshold value is obviously too big, eg a > circle becomes a square! > > As the doc states that "normally you should not need to modify it", i > was reluctant to change it, but then I realised that maybe this > default value is actually well adjusted in the context of QWidget, > where the unit of measure is "pixel". In a QGraphicsScene the unit is > arbitrary. > If I'm right, there could be potentially a problem as well if the > scene object is too big, eg, a circle will be rendered as a regular > polygon with thousands of edges. So it all boil down to find the > correct threshold so that both small and big (in scene coordinates) > will be rendered in the view (pixel coordinates), using say 26 edges > polygon (icosikaihexagon [1][2] ;)) > > Could anyone shed a bit of light on what "well adjusted" mean and how > to actually adjust it to s specific use case? Is this threshold > actually expressed in a pixel-related unit of measure? Is it a ratio > of something (0.0 to 1.0) ?
I've been wondering the same actually, though it was a long time ago. The QPainterPathStroker has no information about which scale you intend to paint the path, so I guess like you say, it must make some assumption based on pixel units and a regular screen size. For details of how it adjusts this value I think you'll have to look at the code. But maybe the docs should be extended a bit. Elvis > > Thanks, > Chris > > [1] https://www.voltage.com/math-2/approximating-a-circle-with-a-polygon/ > [2] http://mathforum.org/dr.math/faq/faq.polygon.names.html > _______________________________________________ > Interest mailing list > Interest@qt-project.org > http://lists.qt-project.org/mailman/listinfo/interest
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