Force 4:3 in fullscreen mode

Does anybody know how to force 4:3 when enabling fullscreen mode using OpenGL and 开发者_StackOverflow社区AGL?

Create a fullscreen window, then call glViewport with the approriate parameters in order to select the 4:3 area.

Create a regular context at the native resolution of the display and then make a FBO with the desired aspect ratio, render your scene to that, and then use the FBO texture to render a quad with the correct aspect ratio to the screen.