anchor.diff:  
     patches = [
       (fetchurl {
  -      url = "mirror://sourceforge/libpng-apng/libpng16/1.6.26/libpng-1.6.26-apng.patch.gz";
  -      sha256 = "01dec904d91ee8c90a9a78f253d01d8fac0e37a3f4beacb60e136ea7c814d72c";
  +      url = "mirror://sourceforge/libpng-apng/libpng16/1.6.30/libpng-1.6.30-apng.patch.gz";
  +      sha256 = "1a6359b1fa7855ed8afcf11be57725093d29cc7ee921c8e030c59d63c565d91a";
       })
     ];
   
  
positive.code: }:
  
  let
    version = "1.6.29";
  in
  stdenv.mkDerivation rec {
    name = "libpng-${version}";
  
negative.code:   src = fetchurl {
      url = "mirror://sourceforge/libpng/libpng16/${version}/${name}.tar.xz";
      hashOutput = false;
      sha256 = "267c332ffff70cc599d3929207869f698798f1df143aa5f9597b007c14353666";
    };
  
    buildInputs = [
  