/* setup gbm egl surface */
   ctx_attr[cn++] = EGL_CONTEXT_CLIENT_VERSION;
   ctx_attr[cn++] = 2;

   if (_extn_have_context_priority)
     {
        ctx_attr[cn++] = EGL_CONTEXT_PRIORITY_LEVEL_IMG;
        ctx_attr[cn++] = EGL_CONTEXT_PRIORITY_HIGH_IMG;
     }
   ctx_attr[cn++] = EGL_NONE;

   cfg_attr[n++] = EGL_RENDERABLE_TYPE;
   cfg_attr[n++] = EGL_OPENGL_ES2_BIT;
   cfg_attr[n++] = EGL_SURFACE_TYPE;
   cfg_attr[n++] = EGL_WINDOW_BIT;

   cfg_attr[n++] = EGL_RED_SIZE;
   cfg_attr[n++] = 1;
   cfg_attr[n++] = EGL_GREEN_SIZE;
   cfg_attr[n++] = 1;
   cfg_attr[n++] = EGL_BLUE_SIZE;
   cfg_attr[n++] = 1;


   cfg_attr[n++] = EGL_ALPHA_SIZE;
   if (ob->destination_alpha) cfg_attr[n++] = 1;
   else cfg_attr[n++] = 0;
   cfg_attr[n++] = EGL_NONE;