anchor.diff:      "--${boolEn opengl-dummy.glx}-xcb-shm"
       "--disable-qt"
       "--disable-quartz"
  -    "--disable-quartz-font"
  -    "--disable-quartz-image"
  -    "--disable-win32"
  -    "--disable-win32-font"
  +    "--disable-quartz-font"  # macOS
  +    "--disable-quartz-image"  # macOS
  +    "--disable-win32"  # Windows
  +    "--disable-win32-font"  # Windows
       # TODO: package skia
       "--disable-skia"
       "--disable-os2"
  
positive.code:     opengl-dummy
      xorg.pixman
      zlib
    ]  ++ optionals opengl-dummy.glx [
      libx11
      libxcb
      libxext
  
negative.code:        Freetype `-I' cflags from being propagated. */ ''
        sed -i src/cairo.pc.in \
          -e 's|^Cflags:\(.*\)$|Cflags: \1 -I${freetype}/include/freetype2 -I${freetype}/include|g'
      '' + optionalString (!opengl-dummy.glx) /* tests and perf tools require Xorg */ ''
        sed -i Makefile.am \
          -e '/^SUBDIRS/ s#boilerplate test perf# #'
      '';
  