Is there any way I can trigger onPaint?

Hi,
this is about C++. I have a Slate class in which I have overloaded the onPaint function and use MakeText, MakeLine to draw things. This all works but onPaint is called different number of times per second. Depending on the ticks so depending on the FPS. But I want the drawing to be constant.

I could not find a way to influence this. Do any of you have an idea?