anchor.diff:  , libdrm, xorg, wayland, udev, llvm, libffi
   , libvdpau
   , enableTextureFloats ? false # Texture floats are patented, see docs/patents.txt
  -, enableR600LlvmCompiler ? false
  +, enableR600LlvmCompiler ? false # we would need currently unreleased LLVM or patches
  +, enableExtraFeatures ? false # add ~15 MB to mesa_drivers
   }:
   
   if ! stdenv.lib.lists.elem stdenv.system stdenv.lib.platforms.mesaPlatforms then
  
positive.code: 
    src = fetchurl {
      url = "ftp://ftp.freedesktop.org/pub/mesa/${version}/MesaLib-${version}.tar.bz2";
      sha256="1ns366armqmp2bxj1l7fff95v22b5z9mnkyykbdj81lhg9gi3586"; # 9.1.2
    };
  
    prePatch = "patchShebangs .";
  
negative.code:     "--enable-shared-glapi" "--enable-shared-gallium"
      "--enable-driglx-direct" # seems enabled anyway
      "--enable-gallium-llvm" "--with-llvm-shared-libs"
      "--enable-xa" # used in vmware driver
  
      "--with-dri-drivers=i965,r200,radeon"
      "--with-gallium-drivers=i915,nouveau,r300,r600,svga,swrast" # radeonsi complains about R600 missing in LLVM
  