Qwt User's Guide 5.2.2

Deprecated List

Member QwtPlot::clear ()
Use QwtPlotDeict::detachItems instead

Class QwtPlotPrintFilter
In Qwt 5.0 the design of QwtPlot allows/recommends writing individual QwtPlotItems, that are not known to QwtPlotPrintFilter. So this concept is outdated and QwtPlotPrintFilter will be removed/replaced in Qwt 6.x.