On Qwt-6.1.4 there is built-in library for MathML like qwt_mathml_text_engine.cpp And after writing such a code:
QwtPlot* plot = new QwtPlot(QwtText("<apply><sin/><ci>x</ci></apply>", QwtText::MathMLText));
ui->gridLayout->addWidget(plot);
There is no math special symbols in plot title.
How to make it rendering formulas in proper way using MathML in Qwt?