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diff --git a/Build/source/libs/harfbuzz/harfbuzz-src/CONFIG.md b/Build/source/libs/harfbuzz/harfbuzz-src/CONFIG.md new file mode 100644 index 00000000000..98be0363e69 --- /dev/null +++ b/Build/source/libs/harfbuzz/harfbuzz-src/CONFIG.md @@ -0,0 +1,132 @@ +# Configuring HarfBuzz + +Most of the time you will not need any custom configuration. The configuration +options provided by `configure` or `cmake` should be enough. In particular, +if you just want HarfBuzz library plus hb-shape / hb-view utilities, make sure +FreeType and Cairo are available and found during configuration. + +If you are building for distribution, you should more carefully consider whether +you need Glib, ICU, Graphite2, as well as CoreText / Uniscribe / DWrite. Make +sure the relevant ones are enabled. + +If you are building for custom environment (embedded, downloadable app, etc) +where you mostly just want to call `hb_shape()` and the binary size of the +resulting library is very important to you, the rest of this file guides you +through your options to disable features you may not need, in exchange for +binary size savings. + +## Compiler Options + +Make sure you build with your compiler's "optimize for size" option. On `gcc` +this is `-Os`, and can be enabled by passing `CXXFLAGS=-Os` either to `configure` +(sticky) or to `make` (non-sticky). On clang there is an even more extreme flag, +`-Oz`. + +HarfBuzz heavily uses inline functions and the optimize-size flag can make the +library smaller by 20% or more. Moreover, sometimes, based on the target CPU, +the optimize-size builds perform *faster* as well, thanks to lower code +footprint and caching effects. So, definitely try that even if size is not +extremely tight but you have a huge application. For example, Chrome does +that. Note that this configuration also automatically enables certain internal +optimizations. Search for `HB_OPTIMIZE_SIZE` for details, if you are using +other compilers, or continue reading. + +Another compiler option to consider is "link-time optimization", also known as +'lto'. To enable that, with `gcc` or `clang`, add `-flto` to both `CXXFLAGS` +and `LDFLAGS`, either on `configure` invocation (sticky) or on `make` (non-sticky). +This, also, can have a huge impact on the final size, 20% or more. + +Finally, if you are making a static library build or otherwise linking the +library into your app, make sure your linker removes unused functions. This +can be tricky and differ from environment to environment, but you definitely +want to make sure this happens. Otherwise, every unused public function will +be adding unneeded bytes to your binary. + +Combining the above three build options should already shrink your library a lot. +The rest of this file shows you ways to shrink the library even further at the +expense of removing functionality (that may not be needed). The remaining +options are all enabled by defining pre-processor macros, which can be done +via `CXXFLAGS` or `CPPFLAGS` similarly. + + +## Unicode-functions + +Access to Unicode data can be configured at compile time as well as run-time. +By default, HarfBuzz ships with its own compact subset of properties from +Unicode Character Database that it needs. This is a highly-optimized +implementation that depending on compile settings (optimize-size or not) +takes around ~40kb or ~60kb. Using this implementation (default) is highly +recommended, as HarfBuzz always ships with data from latest version of Unicode. +This implementation can be disabled by defining `HB_NO_UCD`. + +For example, if you are enabling ICU as a built-in option, or GLib, those +can provide Unicode data as well, so defining `HB_NO_UCD` might save you +space without reducing functionality (to the extent that the Unicode version +of those implementations is recent.) + +If, however, you provide your own Unicode data to HarfBuzz at run-time by +calling `hb_buffer_set_unicode_funcs` on every buffer you create, and you do +not rely on `hb_unicode_funcs_get_default()` results, you can disable the +internal implementation by defining both `HB_NO_UCD` and `HB_NO_UNICODE_FUNCS`. +The latter is needed to guard against accidentally building a library without +any default Unicode implementations. + + +## Font-functions + +Access to certain font functionalities can also be configured at run-time. By +default, HarfBuzz uses an efficient internal implementation of OpenType +functionality for this. This internal implementation is called `hb-ot-font`. +All newly-created `hb_font_t` objects by default use `hb-ot-font`. Using this +is highly recommended, and is what fonts use by default when they are created. + +Most embedded uses will probably use HarfBuzz with FreeType using `hb-ft.h`. +In that case, or if you otherwise provide those functions by calling +`hb_font_set_funcs()` on every font you create, you can disable `hb-ot-font` +without loss of functionality by defining `HB_NO_OT_FONT`. + + +## Thread-safety + +By default HarfBuzz builds as a thread-safe library. The exception is that +the `HB_TINY` predefined configuring (more below) disables thread-safety. + +If you do /not/ need thread-safety in the library (eg. you always call into +HarfBuzz from the same thread), you can disable thread-safety by defining +`HB_NO_MT`. As noted already, this is enabled by `HB_TINY`. + + +## Pre-defined configurations + +The [`hb-config.hh`](src/hb-config.hh) internal header supports three +pre-defined configurations as well grouping of various configuration options. +The pre-defined configurations are: + + * `HB_MINI`: Disables shaping of AAT as well as legacy fonts. Ie. it produces + a capable OpenType shaper only. + + * `HB_LEAN`: Disables various non-shaping functionality in the library, as well + as esoteric or rarely-used shaping features. See the definition for details. + + * `HB_TINY`: Enables both `HB_MINI` and `HB_LEAN` configurations, as well as + disabling thread-safety and debugging, and use size-optimized data tables. + + +## Tailoring configuration + +Most of the time, one of the pre-defined configuration is exactly what one needs. +Sometimes, however, the pre-defined configuration cuts out features that might +be desired in the library. Unfortunately there is no quick way to undo those +configurations from the command-line. But one can add a header file called +`config-override.h` to undefine certain `HB_NO_*` symbols as desired. Then +define `HAVE_CONFIG_OVERRIDE_H` to make `hb-config.hh` include your configuration +overrides at the end. + + +## Notes + +Note that the config option `HB_NO_CFF`, which is enabled by `HB_LEAN` and +`HB_TINY` does /not/ mean that the resulting library won't work with CFF fonts. +The library can shape valid CFF fonts just fine, with or without this option. +This option disables (among other things) the code to calculate glyph exntents +for CFF fonts. |