d5c56723d1
libopencv_imgproc grew noticeably with the HarfBuzz-based text engine. Measured on
macOS/arm64 (clang, Release, stripped) the text-related part of the library was
~830 KB: HarfBuzz 486 KB, the two Rubik fonts 296 KB, the engine ~25 KB, plus ~2 MB
of WenQuanYi when WITH_UNIFONT=ON (the previous default). With GCC and an unstripped
.so on Linux the HarfBuzz part alone is 700+ KB.
This patch brings it down to ~550 KB by default (HarfBuzz 377 KB + Rubik 146 KB +
engine 30 KB) without dropping functionality:
* 3rdparty/harfbuzz: build with -Os -fno-exceptions -fno-rtti -fno-threadsafe-statics
(like HarfBuzz's own build; shaping speed is irrelevant thanks to the glyph cache)
and HB_NO_VAR_COMPOSITES (VARC table, a 2024 format with no real fonts yet).
Variable-font support (wght axis etc.) is untouched. -22% of HarfBuzz code.
* Only the "sans" font (Rubik) is compiled into imgproc by default. Rubik Italic and
WenQuanYi Micro Hei became optional: WITH_ITALICFONT (new) and WITH_UNIFONT are
both OFF now. The build summary lists the built-in fonts.
* New API cv::FontFace::setBuiltinFont(name, path) fills or replaces any of the
three built-in slots ("sans", "italic", "uni") with an external font file. The
registered font takes part in the automatic fallback chain exactly like a
compiled-in one, so users can get CJK text or a true italic without rebuilding
OpenCV. The registry is process-wide; each thread's engine reloads its slots
lazily (generation counter), and the glyph cache is dropped on reload since
hb_font pointers are part of its key.
* "italic" resolves to "sans" when no italic font is built in or registered, so
FONT_ITALIC / FONT_HERSHEY_SCRIPT_* in the legacy putText keep working (upright).
* Fix: a character not covered by any font used to be drawn as '?' taken from the
last built-in slot, which can be empty now; the '?' is looked up like any other
character (user font first).
* Tests: opencv_test_imgproc registers Rubik-Italic.ttf.gz and
WenQuanYiMicroHei.ttf.gz from opencv_extra (testdata/highgui/drawing) as the
"italic"/"uni" slots, so Drawing.ttf_text reproduces the reference picture 1:1
with the default build and the legacy hershey-font tests are unchanged.
Drawing.builtin_font_slots covers the new API. Tests skip if the fonts are absent.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
HarfBuzz
HarfBuzz started as a text shaping engine but has grown into a
full font platform — the ffmpeg of text shaping. It primarily
supports OpenType, but also Apple Advanced Typography.
HarfBuzz shapes the majority of text on modern screens.
HarfBuzz is optimized for robustness, correctness, and performance — in that order. Achieve all.
Try it live at harfbuzz-world.cc — an interactive playground for shaping, subsetting, rasterization, vector output, and GPU rendering, all running in your browser.
Here is a quick map of its components:
Core libraries
| Library | Description |
|---|---|
| libharfbuzz | Text shaping, draw API, paint API. Highly configurable (see CONFIG.md). Optional integration backends compiled in: hb-ft (FreeType), hb-coretext (macOS), hb-uniscribe (Windows), hb-directwrite (Windows), hb-gdi (Windows), hb-glib, hb-graphite2. |
| libharfbuzz-subset | Font subsetting and variable-font instancing. |
Auxiliary libraries
| Library | Description |
|---|---|
| libharfbuzz-icu | ICU Unicode integration. |
| libharfbuzz-cairo | Cairo rendering integration. |
| libharfbuzz-gobject | GObject/GI bindings. |
Experimental libraries
| Library | Description |
|---|---|
| libharfbuzz-raster | Glyph rasterization to bitmaps, including color fonts. Uses hb-draw and hb-paint. |
| libharfbuzz-vector | Glyph output to vector formats (currently SVG), including color fonts. Uses hb-draw and hb-paint. |
| libharfbuzz-gpu | Encodes glyph outlines for GPU rasterization (Slug algorithm). Provides shader sources in GLSL, WGSL, MSL, and HLSL. Live demo. |
Notable missing feature: font hinting (including autohinting) is not implemented. For hinted rasterization, use FreeType or Skrifa.
For simplified builds, amalgamated sources are available:
harfbuzz.cc (just libharfbuzz), harfbuzz-subset.cc (just
libharfbuzz-subset), or harfbuzz-world.cc (everything, driven
by a custom hb-features.h). For a live in-browser playground
plus a worked example of the world.cc single-file build, see
harfbuzz-world.cc.
Command-line tools
| Tool | Description |
|---|---|
| hb-shape | Shape text and display glyph output. |
| hb-view | Render shaped text to an image. |
| hb-subset | Subset and optimize fonts. |
| hb-info | Display font metadata. |
| hb-raster | Render glyphs to bitmap images. |
| hb-vector | Render glyphs to vector formats (SVG). |
| hb-gpu | Interactive GPU text rendering. |
The canonical source tree and bug trackers are available on github. Both development and user support discussion around HarfBuzz happen on github as well.
For license information, see COPYING.
API stability
The API that comes with hb.h will not change incompatibly. Other, peripheral,
headers are more likely to go through minor modifications, but again, we do our
best to never change API in an incompatible way. We will never break the ABI.
The API and ABI are stable even across major version number jumps. In fact, current HarfBuzz is API/ABI compatible all the way back to the 0.9.x series. If one day we need to break the API/ABI, that would be called a new library.
As such, we bump the major version number only when we add major new features, the minor version when there is new API, and the micro version when there are bug fixes.
Documentation
For user manual as well as API documentation, check: https://harfbuzz.github.io
Download
Tarball releases and Win32/Win64 binary bundles are available on the github releases page.
Development
For build information, see BUILD.md.
For custom configurations, see CONFIG.md.
For testing and profiling, see TESTING.md.
For using with Python, see README.python.md. There is also uharfbuzz.
For cross-compiling to Windows from Linux or macOS, see README.mingw.md.
To report bugs or submit patches please use github issues and pull-requests.
Developer documents
To get a better idea of where HarfBuzz stands in the text rendering stack you may want to read State of Text Rendering 2024. Here are a few presentation slides about HarfBuzz over the years:
- 2026 – HarfBuzz at 20!
- 2016 – Ten Years of HarfBuzz
- 2014 – Unicode, OpenType, and HarfBuzz: Closing the Circle
- 2012 – HarfBuzz, The Free and Open Text Shaping Engine
- 2009 – HarfBuzz: the Free and Open Shaping Engine
More presentations and papers are available on behdad's website. In particular, the following studies are relevant to HarfBuzz development:
- 2025 – AAT layout caches
- 2025 – OpenType Layout lookup caches
- 2025 – Introducing HarfRust
- 2025 – Subsetting
- 2025 – Caching
- 2025 –
hb-decycler - 2022 –
hb-iter - 2022 – A C library written in C++
- 2022 – The case of the slow
hb-ft>h_advancefunction - 2022 – PackTab: A static integer table packer
- 2020 – HarfBuzz OT+AAT "Unishaper"
- 2014 – Building the Indic Shaper
- 2012 – Memory Consumption
Name
HarfBuzz /hærfˈbɒːz/
From Persian حرف (Harf: letter) and باز (Buzz: open). Transliteration of the Persian calque for OpenType.
As a noun: The Open Source text shaping engine.
As an adjective: Insincerely talkative; glib. A nod to the GNOME project where HarfBuzz originates from.
The logo shows حرفباز in the IranNastaliq font, on a Damascus steel background.
Background: Originally there was this font format called TrueType. People and companies started calling their type engines all things ending in Type: FreeType, CoolType, ClearType, etc. And then came OpenType, which is the successor of TrueType. So, for my OpenType implementation, I decided to stick with the concept but use the Persian translation. Which is fitting given that Persian is written in the Arabic script, and OpenType is an extension of TrueType that adds support for complex script rendering, and HarfBuzz is an implementation of OpenType text shaping.
Users
HarfBuzz is used in Android, Chrome, ChromeOS, Firefox, Flutter, GNOME, GTK+, KDE, Qt, LibreOffice, OpenJDK, XeTeX, Adobe Photoshop, Illustrator, InDesign, Microsoft Edge, Amazon Kindle, PlayStation, Godot Engine, Unreal Engine, Figma, Canva, QuarkXPress, Scribus, smart TVs, car displays, and many other places.
Distribution
Packaging status of HarfBuzz
