QPainter and C function

I have a C function from an C program that I call from a widget.

This works! I use extern C to include the .h and call my function.

The problem is this function contain some calls to draw lines. I would like to draw lines with QPainter.

So I call my C function from my widget and how is possible to call drawLine from QPainter from my C function.

you can't really.

(Unless you provide a C interface that calls QPainter for you and call that (new) interface from your C code... but if you have to modify the C code, why not turn it into C++ right away?)

The code is very big with lot of global variables so it is difficult to rewrite it in c++.But I can modifie the c code to call a draw line function but I dont know how to do that...

The only way is to provide some global environment on which the C functions can operate but that's a very ugly solution.

Code:

---

QPainter *globalPainter;
 
void drawLine(int x1, int y1, int x2, int y2){
  globalPainter->drawLine(x1, y1, x2, y2);
}

---

Of course the painter has to be properly initialized and it can't operate on QWidget.

I find a solution.

I stock a global list of points computed from my C function call from QPainter. And I return than to qpainter to display them.