A HiDPI-ready, minimal preview renderer for viewing variable TTF fonts using HarfBuzz and FreeType (and SDL3 purely for preview). Included are the most common open-source free-use variable fonts, which demonstrate a variety of variable parameters and style sets.
This code is dedicated to the public domain, or licenses under CC0 (your choice). Included fonts have their own licenses, see licenses/.
Install deps, for example on macOS:
brew update
brew install freetype
brew install harfbuzz
brew install sdl3Note that SDL3 and HB are in active development. This has been tested on macOS 15.4.1 with HarfBuzz 11.1.0 and SDL 3.2.10. You may want to install HEAD versions.
Build and run:
make
./demo_sdl3 font.ttf # [#RRGGBB]- Q/A: change weight axis value
- W/S: change width axis value
- E/D: change slant angle
Remember that most variable fonts still come in two versions: Regular and Italic, because the default shear-only transform does not usually yield acceptable visuals for italics.
The included demo font Mona Sans Combined for example can slant on-demand, whereas Inter cannot (hence the second Italic version).
By convention, the font file name should include the supported parameters. Native variable fonts (such as Science Gothic) contain many more parameters (contrast, etc.), but this previewer only considers the three most common listed above. Some fonts may be highly parametric, see e.g. Decovar.
The previewer auto-detects the valid value ranges for each parameter.
Style sets change the appearance of one or more font element, e.g. double-storey a. The previewer detects all supported style sets and you can use 1 through 9 to enable/disable them.