Ok. Sorry. I’d slept and forgotten that you’d mentioned that in your original post.
I looked back at some test code where I’d done exactly that (created an EGL context using EGL_DEFAULT_DISPLAY for rendering to an on-screen PBuffer), and there’s a trick to get this to work.
The EGL/OpenGL libs you’re linked with must be able to open kernel “special” files related to the graphics driver such as
/dev/dri/renderD128. On my Linux system, these are owned by group
video. So by adding my username to the
video group, the EGL/OpenGL libs running as me were then able to open these files and successfully create an EGL context, even in cases where I was not the user who had started the X server.
Once your username has the required access, then this should work:
EGLDisplay display = eglGetDisplay( EGL_DEFAULT_DISPLAY );
assert( display != EGL_NO_DISPLAY );
EGLint egl_major, egl_minor;
EGLBoolean success = eglInitialize( display, &egl_major, &egl_minor );
assert( success );