Is there any possibility to draw e.g. a line and for each pixel of this line the inverse color of the framebuffer should be used?
use
glBlendFunc(GL_ONE_MINUS_DST_COLOR, GL_ZERO);
glEnable(GL_BLEND);
that should do it
Chris
Danke 
Danke?? Hier sprechen sicher viele Leute Deutsch 
Danke?? I’m sure many people speak German in here