Dense Qwt curves with dotted or dashed line style generally look solid.

[philw]

Curves with many points plotted with a Dotted or Dashed line style display as SOLID lines (not dotted or dashed) at normal zoom levels. We're using Qwt 6.1.3 and Qt 5.5.1 on Windows.

One thing I thought to try was turning ON the "FilterPoints" PaintAttribute on the QwtPlotCurves. But I found that these curves already had it on (by default). (And turning it off didn't fix the problem).

The images below show one "Step" curve and one "Line" curve with many points. This sequence of seven images progressively zooms in. Point symbols are turned on half-way through to show the density of the series data.

Is there any way of having the Dotted and Dashed line styles work for dense curve data?

See this webpage, or some attached images below.
http://cadswes2.colorado.edu/~philw/...robImages.html

DenseTestThreeSmall.gif DenseTestThree_01.png DenseTestThree_03.png
DenseTestThree_04.png DenseTestThree_06.png

[Uwe]

Curves with many points plotted with a Dotted or Dashed line style display as SOLID lines (not dotted or dashed) at normal zoom levels. We're using Qwt 6.1.3 and Qt 5.5.1 on Windows.

If your points are closer than the widths of the dashes/dots it is like this - that's how QPainter works.

So what you need is a curve interpolation, that weeds out points. In general QwtWeedingCurveFitter offers such an algo ( Douglas-Peucker ), but is an expensive one and should better be used in advance outside of the replot cycle, when having many points.

Uwe