Install hb-cairo.h and define HB_HAS_CAIRO.
The intended use for hb-features.h is to be included standalone, so we can't put the single-include guards in here.
This header has defines for all the optional dependendencies that come with their own Harfbuzz headers, so you can do: #include <hb-features.h> #ifdef HB_HAS_DIRECTWRITE #include <hb-directwrite.h> #endif