HarfBuzz text shaping engine
http://harfbuzz.github.io/
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158 lines
7.4 KiB
158 lines
7.4 KiB
# Configuring HarfBuzz |
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Most of the time you will not need any custom configuration. The configuration |
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options provided by `meson` should be enough. In particular, if you just want |
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HarfBuzz library plus hb-shape / hb-view utilities, make sure FreeType and Cairo |
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are available and found during configuration. |
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If you are building for distribution, you should more carefully consider whether |
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you need Glib, ICU, Graphite2, as well as CoreText / Uniscribe / DWrite. Make |
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sure the relevant ones are enabled. |
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If you are building for custom environment (embedded, downloadable app, etc) |
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where you mostly just want to call `hb_shape()` and the binary size of the |
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resulting library is very important to you, the rest of this file guides you |
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through your options to disable features you may not need, in exchange for |
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binary size savings. |
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## Compiler Options |
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Make sure you build with your compiler's "optimize for size" option. On `gcc` |
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this is `-Os`, and can be enabled by passing `CXXFLAGS=-Os`. On clang there |
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is an even more extreme flag, `-Oz`. Meson also provides `--buildtype=minsize` |
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for more convenience. |
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HarfBuzz heavily uses inline functions and the optimize-size flag can make the |
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library smaller by 20% or more. Moreover, sometimes, based on the target CPU, |
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the optimize-size builds perform *faster* as well, thanks to lower code |
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footprint and caching effects. So, definitely try that even if size is not |
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extremely tight but you have a huge application. For example, Chrome does |
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that. Note that this configuration also automatically enables certain internal |
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optimizations. Search for `HB_OPTIMIZE_SIZE` for details, if you are using |
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other compilers, or continue reading. |
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Another compiler option to consider is "link-time optimization", also known as |
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'lto'. To enable that, feel free to use `-Db_lto=true` of meson. |
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This, also, can have a huge impact on the final size, 20% or more. |
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Finally, if you are making a static library build or otherwise linking the |
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library into your app, make sure your linker removes unused functions. This |
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can be tricky and differ from environment to environment, but you definitely |
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want to make sure this happens. Otherwise, every unused public function will |
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be adding unneeded bytes to your binary. The following pointers might come |
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handy: |
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* https://lwn.net/Articles/741494/ (all of the four-part series) |
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* https://elinux.org/images/2/2d/ELC2010-gc-sections_Denys_Vlasenko.pdf |
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Combining the above three build options should already shrink your library a lot. |
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The rest of this file shows you ways to shrink the library even further at the |
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expense of removing functionality (that may not be needed). The remaining |
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options are all enabled by defining pre-processor macros, which can be done |
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via `CXXFLAGS` or `CPPFLAGS` similarly. |
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## Unicode-functions |
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Access to Unicode data can be configured at compile time as well as run-time. |
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By default, HarfBuzz ships with its own compact subset of properties from |
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Unicode Character Database that it needs. This is a highly-optimized |
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implementation that depending on compile settings (optimize-size or not) |
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takes around ~40kb or ~60kb. Using this implementation (default) is highly |
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recommended, as HarfBuzz always ships with data from latest version of Unicode. |
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This implementation can be disabled by defining `HB_NO_UCD`. |
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For example, if you are enabling ICU as a built-in option, or GLib, those |
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can provide Unicode data as well, so defining `HB_NO_UCD` might save you |
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space without reducing functionality (to the extent that the Unicode version |
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of those implementations is recent.) |
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If, however, you provide your own Unicode data to HarfBuzz at run-time by |
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calling `hb_buffer_set_unicode_funcs` on every buffer you create, and you do |
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not rely on `hb_unicode_funcs_get_default()` results, you can disable the |
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internal implementation by defining both `HB_NO_UCD` and `HB_NO_UNICODE_FUNCS`. |
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The latter is needed to guard against accidentally building a library without |
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any default Unicode implementations. |
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## Font-functions |
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Access to certain font functionalities can also be configured at run-time. By |
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default, HarfBuzz uses an efficient internal implementation of OpenType |
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functionality for this. This internal implementation is called `hb-ot-font`. |
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All newly-created `hb_font_t` objects by default use `hb-ot-font`. Using this |
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is highly recommended, and is what fonts use by default when they are created. |
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Most embedded uses will probably use HarfBuzz with FreeType using `hb-ft.h`. |
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In that case, or if you otherwise provide those functions by calling |
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`hb_font_set_funcs()` on every font you create, you can disable `hb-ot-font` |
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without loss of functionality by defining `HB_NO_OT_FONT`. |
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## Shapers |
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Most HarfBuzz clients use it for the main shaper, called "ot". However, it |
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is legitimate to want to compile HarfBuzz with only another backend, eg. |
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CoreText, for example for an iOS app. For that, you want `HB_NO_OT_SHAPE`. |
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If you are going down that route, check if you want `HB_NO_OT`. |
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This is very rarely what you need. Make sure you understand exactly what you |
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are doing. |
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Defining `HB_NO_FALLBACK_SHAPE` however is pretty harmless. That removes the |
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(unused) "fallback" shaper. This is defined by the `HB_TINY` profile already |
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(more below). |
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## Thread-safety |
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By default HarfBuzz builds as a thread-safe library. The exception is that |
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the `HB_TINY` predefined configuration (more below) disables thread-safety. |
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If you do *not* need thread-safety in the library (eg. you always call into |
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HarfBuzz from the same thread), you can disable thread-safety by defining |
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`HB_NO_MT`. As noted already, this is enabled by `HB_TINY`. |
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## Pre-defined configurations |
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The [`hb-config.hh`](src/hb-config.hh) internal header supports three |
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pre-defined configurations as well grouping of various configuration options. |
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The pre-defined configurations are: |
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* `HB_MINI`: Disables shaping of AAT as well as legacy fonts. Ie. it produces |
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a capable OpenType shaper only. |
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* `HB_LEAN`: Disables various non-shaping functionality in the library, as well |
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as esoteric or rarely-used shaping features. See the definition for details. |
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* `HB_TINY`: Enables both `HB_MINI` and `HB_LEAN` configurations, as well as |
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disabling thread-safety and debugging, and use even more size-optimized data |
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tables. |
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## Tailoring configuration |
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Most of the time, one of the pre-defined configuration is exactly what one needs. |
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Sometimes, however, the pre-defined configuration cuts out features that might |
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be desired in the library. Unfortunately there is no quick way to undo those |
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configurations from the command-line. |
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However, configuration can still be overridden from a file. To do that, add your |
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override instructions (mostly `undef` instructions) to a header file and define |
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the macro `HB_CONFIG_OVERRIDE_H` to the string containing to that header file's |
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name. HarfBuzz will then include that file at the appropriate place during |
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configuration. |
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Up until HarfBuzz 3.1.2 the the configuration override header file's name was |
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fixed and called `config-override.h`, and was activated by defining the macro |
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`HAVE_CONFIG_OVERRIDE_H`. That still works. |
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## Notes |
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Note that the config option `HB_NO_CFF`, which is enabled by `HB_LEAN` and |
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`HB_TINY` does *not* mean that the resulting library won't work with CFF fonts. |
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The library can shape valid CFF fonts just fine, with or without this option. |
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This option disables (among other things) the code to calculate glyph extents |
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for CFF fonts, which many clients might not need.
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