anchor.diff:      "--enable-texture-float"
       (enableFeature stdenv.isLinux "dri3")
       (enableFeature stdenv.isLinux "nine") # Direct3D in Wine
  -    "--enable-libglvnd"
  +    (enableFeature stdenv.isLinux "libglvnd")
       "--enable-dri"
       "--enable-driglx-direct"
       "--enable-gles1"
  
positive.code:     inherit libdrm version;
      inherit (libglvnd) driverLink;
  
      stubs = stdenv.mkDerivation {
        name = "libGL-${libglvnd.version}";
        outputs = [ "out" "dev" ];
  
        # Use stub libraries from libglvnd and headers from Mesa.
        buildCommand = ''
          mkdir -p $out/nix-support
          ln -s ${libglvnd.out}/lib $out/lib
  
  
negative.code:         genPkgConfig egl EGL
          genPkgConfig glesv1_cm GLESv1_CM
          genPkgConfig glesv2 GLESv2
        '';
      };
    };
  