anchor.diff:    nativeBuildInputs = [ pkg-config yasm ];
   
     buildInputs = [ freetype fribidi harfbuzz ]
  -    ++ optional encaSupport enca
       ++ optional fontconfigSupport fontconfig
       ++ optional stdenv.isDarwin libiconv;
   
  
positive.code: { lib, stdenv, fetchurl, pkg-config, yasm
  , freetype, fribidi, harfbuzz
  , encaSupport ? true, enca ? null # enca support
  , fontconfigSupport ? true, fontconfig ? null # fontconfig support
  , rasterizerSupport ? false # Internal rasterizer
  , largeTilesSupport ? false # Use larger tiles in the rasterizer
  , libiconv
  }:
  
  assert encaSupport -> enca != null;
  assert fontconfigSupport -> fontconfig != null;
  
  let
  
negative.code:   };
  
    configureFlags = [
      (mkFlag fontconfigSupport "fontconfig")
      (mkFlag rasterizerSupport "rasterizer")
      (mkFlag largeTilesSupport "large-tiles")
  