how to plot inequalities with QWT?

Hello,


I would like to plot inequality functions (such as 3x^2 - 5y <= 0 ) by means of Qwt classes, but don't know how to do so sufficiently.

First, I had a simple solution, whereas I reformed the inequality to equality (3x^2 - 5y = 0 ) and then separated the variables (y = 3/5 x^2 ). Moreover, I stored the type of inequality, whether it is > or < in order to shade the infeasible region afterwards. The changed function (y = 3/5 x^2 ) could be plotted then with QwtPlotCurves after setting Data like in "SimpleData" example. Unfortunately, I don't like such solution anymore because I can only plot y against x, but not vice versa. Furthermore, it is necessary to reform the function, which is not always possible or very difficult to do.

My question now is, could you suggest me another (better) approach how to graph inequalities?

Thanks in advance.


best regards,


Vitali Anselm