c++ - Qt renderText() functions bug - text crashes -

c++ - Qt renderText() functions bug - text crashes -

i utilize qglwidget draw graphics in qt, , need render text within widget.

the problem after time, turns from:

to this:

and code looks this:

glpushmatrix(); qglcolor(qt::white); rendertext(-29, 11.0, -8, "tablica wyników", qfont("arial", 12, qfont::light)); ... glpopmatrix();

what's wrong code/function?

c++ qt qglwidget