anchor.diff:  
     cmakeFlags = [
       "-DFREEGLUT_BUILD_DEMOS=OFF"
  -    # FIXME: is glesv1 or glesv2?
  +    # XXX: Cannot build both libglut and libfreeglut-gles.
       "-DFREEGLUT_GLES=${boolOn (
  -      opengl-dummy.egl
  +      glesSupport
  +      && opengl-dummy.egl
         && opengl-dummy.glesv1
         && opengl-dummy.glesv2)}"
     ];
  
positive.code: , lib
  , ninja
  
  , inputproto
  , libx11
  , libxrandr
  
negative.code: , xf86vidmodeproto
  , xorg
  , xproto
  
  , glesSupport ? false
  }:
  
  let
  