Question

Considering QGLWidget (or OpenGL in general), what can be the easiest solution to draw pixels in the inverse color of the screen / frame buffer? In Win32 / MFC environment, I used to use the SetROP2(R2_NOT) with zero pain.

Answer 1

Something like this?:

glEnable(GL_BLEND);
glBlendFunc(GL_ONE_MINUS_DST_COLOR, GL_ZERO);