anchor.diff:  { majorVersion, minorVersion, sourceSha256, patchesToFetch ? [] }:
  -{ stdenv, lib, fetchurl, cmake, libGLU, libGL, libX11, xorgproto, libXt, libtiff
  +{ 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."
  
positive.code:   cmakeFlags = [
      "-DCMAKE_C_FLAGS=-fPIC"
      "-DCMAKE_CXX_FLAGS=-fPIC"
      "-DVTK_USE_SYSTEM_TIFF=1"
      "-DOPENGL_INCLUDE_DIR=${libGL}/include"
      "-DCMAKE_INSTALL_LIBDIR=lib"
  
negative.code: 
    nativeBuildInputs = [ cmake ];
  
    buildInputs = [ libpng libtiff ]
      ++ optionals enableQt [ qtbase qtx11extras qttools ]
      ++ optionals stdenv.isLinux [
        libGLU
  