anchor.diff:      opengl-dummy
       xorg.pixman
       zlib
  -  ]  ++ optionals opengl-dummy.glx [
  +  ] ++ optionals opengl-dummy.glx [
       libx11
       libxcb
       libxext
  
positive.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# #'
      '';
  
negative.code:     "--${boolEn opengl-dummy.glx}-xcb-shm"
      "--disable-qt"
      "--disable-quartz"
      "--disable-quartz-font"  # macOS
      "--disable-quartz-image"  # macOS
      "--disable-win32"  # Windows
      "--disable-win32-font"  # Windows
      # TODO: package skia
      "--disable-skia"
      "--disable-os2"
  