anchor.diff:    outputs = [ "out" "dev" ];
   
     buildInputs =
  -    [ cmake pkgconfig libGLU libGL ocl-icd python3
  +    [ cmake pkgconfig libGLU libGL python3
         # FIXME: these are not actually needed, but the configure script wants them.
         glew xorg.libX11 xorg.libXrandr xorg.libXxf86vm xorg.libXcursor
         xorg.libXinerama xorg.libXi
       ]
  +    ++ lib.optional (!stdenv.isDarwin) ocl-icd
  +    ++ lib.optionals stdenv.isDarwin (with darwin.apple_sdk.frameworks; [OpenCL Cocoa CoreVideo IOKit AppKit AGL ])
       ++ lib.optional cudaSupport cudatoolkit;
   
     cmakeFlags =
       [ "-DNO_TUTORIALS=1"
         "-DNO_REGRESSION=1"
         "-DNO_EXAMPLES=1"
  +      "-DNO_METAL=1" # don’t have metal in apple sdk
  +    ] ++ lib.optionals (!stdenv.isDarwin) [
         "-DGLEW_INCLUDE_DIR=${glew.dev}/include"
         "-DGLEW_LIBRARY=${glew.dev}/lib"
       ] ++ lib.optionals cudaSupport [
  
positive.code:   meta = {
      description = "An Open-Source subdivision surface library";
      homepage = http://graphics.pixar.com/opensubdiv;
      platforms = lib.platforms.linux;
      maintainers = [ lib.maintainers.eelco ];
      license = lib.licenses.asl20;
    };
  
negative.code: { lib, stdenv, fetchurl, fetchFromGitHub, cmake, pkgconfig, xorg, libGLU
  , libGL, glew, ocl-icd, python3
  , cudaSupport ? false, cudatoolkit
  , darwin
  }:
  
  stdenv.mkDerivation rec {
  