With this patch true headless OpenGL rendering is now possible on Linux. It changes the logic of the WITH_HEADLESS build flag. The headless backend is now always available with regular builds and Blender will try to fall back to it if it fails to initialize other backends while in background mode. The headless backend only works on Linux as EGL is not used on Mac or Windows. libepoxy does support windows and mac, so this can perhaps be remedied in the future. Reviewed By: Brecht, Jeroen, Campbell Differential Revision: http://developer.blender.org/D15555