anchor.diff:  
       # Update search path used by pkg-config
       for pc in $dev/lib/pkgconfig/{d3d,dri,xatracker}.pc; do
  -      substituteInPlace "$pc" --replace $out $drivers
  +      if [ -f "$pc" ]; then
  +        substituteInPlace "$pc" --replace $out $drivers
  +      fi
       done
   
       # add RPATH so the drivers can find the moved libgallium and libdricore9
  
positive.code: , eglPlatforms ? [ "x11" "surfaceless" ] ++ lib.optionals stdenv.isLinux [ "wayland" "drm" ]
  , OpenGL, Xplugin
  , withValgrind ? stdenv.hostPlatform.isLinux && !stdenv.hostPlatform.isAarch32, valgrind-light
  }:
  
  /** Packaging design:
  
negative.code:     for js in $drivers/share/vulkan/icd.d/*.json; do
        substituteInPlace "$js" --replace "$out" "$drivers"
      done
    '' + lib.optionalString enableOSMesa ''
      # move libOSMesa to $osmesa, as it's relatively big
      mkdir -p $osmesa/lib
      mv -t $osmesa/lib/ $out/lib/libOSMesa*
    '';
  
    # TODO:
  