anchor.diff:    cmakeFlags = [
       "-DCMAKE_C_FLAGS=-fPIC"
       "-DCMAKE_CXX_FLAGS=-fPIC"
  +    "-DVTK_USE_SYSTEM_PNG=ON"
       "-DVTK_USE_SYSTEM_TIFF=1"
       "-DOPENGL_INCLUDE_DIR=${libGL}/include"
       "-DCMAKE_INSTALL_LIBDIR=lib"
  
positive.code: 
    nativeBuildInputs = [ cmake ];
  
    buildInputs = [ libtiff ]
      ++ optionals enableQt [ qtbase qtx11extras qttools ]
      ++ optionals stdenv.isLinux [
        libGLU
  
negative.code: { majorVersion, minorVersion, sourceSha256, patchesToFetch ? [] }:
  { stdenv, lib, fetchurl, cmake, libGLU, libGL, libX11, xorgproto, libXt, libpng, libtiff
  , fetchpatch
  , enableQt ? false, wrapQtAppsHook, qtbase, qtx11extras, qttools
  , enablePython ? false, pythonInterpreter ? throw "vtk: Python support requested, but no python interpreter was given."
  