Ok Ive been looking in the forum for problems like mine but couldnt find any solution so I decided to post, anyway here is the thing : I had 2 different windows, one that renders 2D images and the other 3D objects, everything was working fine but now I want to have the 2 renders in the same window, so I red about the good glViewport() and everything seems easy, but when I try to implement it, it doesnt work, actually I can see the "first" render and then it turns black not to ever come again, so I wonder if you guys can help me, this is the code : void renderScene() { glClear(GL_COLOR_BUFFER_BIT); // set 3D viewport glViewport(0, n2DWindowHeight, n3DWindowWidth, n3DWindowHeight); gluPerspective(45.0, n3DWindowWidth/n3DWindowHeight, 1.0, 1000.0); renderScene3D(); // set 2D viewport glViewport(0, 0, n2DWindowWidth, n2DWindowHeight); gluOrtho2D(0,n2DWindowWidth,0,n2DWindowHeight); renderScene2D(); glutSwapBuffers(); } void initGlut(int argc, char **argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA); glutInitWindowPosition(10,80); glutInitWindowSize(nWindowWidth,nWindowHeight); glutCreateWindow("Viewer"); gluPerspective(45.0, n3DWindowWidth/n3DWindowHeight, 1.0, 1000.0); glutDisplayFunc(renderScene); glutIdleFunc(idleGLut); glutMainLoop(); } Thw window size is enough to contain both viewports, glClear and glutSwapBuffers are not called within render2D() and render3D(). And one more thing, if I comment the 3 lines concerning the 2D render the 3D render works perfectly, and viceversa. Thanks a lot for your help.

Thats what I'm talking about ;)

Thanks mikeman.