anchor.diff:  
     buildInputs = [ libtiff ]
       ++ optional (qtLib != null) qtLib
  -    ++ optionals stdenv.isLinux [ libGLU_combined libX11 xorgproto libXt ]
  +    ++ optionals stdenv.isLinux [ libGLU libGL libX11 xorgproto libXt ]
       ++ optionals stdenv.isDarwin [ xpc Cocoa CoreServices DiskArbitration IOKit
                                      CFNetwork Security ApplicationServices CoreText
                                      IOSurface ImageIO OpenGL GLUT ];
  
positive.code:   # built and requiring one of the shared objects.
    # At least, we use -fPIC for other packages to be able to use this in shared
    # objects.
    cmakeFlags = [ "-DCMAKE_C_FLAGS=-fPIC" "-DCMAKE_CXX_FLAGS=-fPIC" "-DVTK_USE_SYSTEM_TIFF=1" ]
      ++ optional (qtLib != null) [ "-DVTK_USE_QT:BOOL=ON" ]
      ++ optional stdenv.isDarwin "-DOPENGL_INCLUDE_DIR=${OpenGL}/Library/Frameworks";
  
  
negative.code: { stdenv, fetchurl, cmake, libGLU, libGL, libX11, xorgproto, libXt, libtiff
  , qtLib ? null
  # Darwin support
  , Cocoa, CoreServices, DiskArbitration, IOKit, CFNetwork, Security, GLUT, OpenGL
  