Hello!

As some older posts show, I'm trying to plot some graphs in a embedded linux environment which requires very efficient plotting using Qwt. For now I'm looking how to do this considering Qwt alone, and with this respect I noticed that use replot() constantly wasn't a good idea, so I decided to move towards a way of higher plot efficiency and I came about using QwtPlotDirectPainter.

Here comes my first question: is there another way of improve plotting efficiency than by using QwtPlotDirectPainter instead of QwtPlot::replot()? Is there somewhere, btw, a manual with all tips and tricks of Qwt including those related to plot efficiency?

Now considering this method (using QwtPlotDirectPainter). As the manual states, it draws only the desired, new data (if so configured) without erasing the background. Now this is a little bit inconvenient, for I'll need to repaint only the part of a curve that has new data, but obviously erasing the paintings related to a older value. If one wants to use a invariable points vector for drawing (so when the new data reaches the last point in the vector, it starts populating from 0 again), I wouldn't know how to use QwtPlotDirectPainter for this, leading either to call QwtPlot::replot() each time the points vector is completely changed (such as in the code posted here¹) or having to abandon a fixed sized QVector in favor of a continuously growing QwtPlot.

Second question: is there a way to come around this problem with QwtPlotDirectPainter?



Thanks,

Momergil



¹: http://www.qtcentre.org/threads/5902...ectly?p=262506