Text and fonts

Text is most of what people read in a UI, so BUI takes it seriously. Your app’s text looks the same on Windows, Linux and macOS, and it looks like Blender’s: the same font, rendered with the same settings.

You don’t have to do anything for this. This page explains how it works, how to use other fonts, and the limits worth knowing.

Inter, built in

BUI embeds Inter, the font Blender uses for its interface, right in the library. There’s nothing to install, and no system font can change how your UI looks.

• It’s the variable version of Inter, with an optical-size axis (14 to 32) and a weight axis (100 to 900).
• It’s the default face everywhere: for widgets, for sans-serif and system-ui in CSS, and for any family BUI can’t find.
• UI text is 11 pt at scale 1, Blender’s default, and grows with the UI scale.

Inter is © The Inter Project Authors, under the SIL Open Font License 1.1 (gpu/extern/Inter-LICENSE.txt).

Rendered like Blender’s BLF

Blender draws text with its font library, BLF, on top of FreeType. BUI vendors FreeType 2.13.3 (the version Blender uses) and renders glyphs the way blf_glyph.cc does:

• Light hinting, so stems stay crisp without distorting the shapes.
• Blender’s gamma-1.43 coverage table, so strokes have Blender’s weight.
• Optical size: the variable Inter is set to the text’s size, clamped to the axis as Blender does. UI text gets Inter’s 14 pt design.
• Bold is the font’s weight-700 instance, not a smeared regular.
• No kerning, matching Blender, whose FreeType is built without GPOS kerning.
• Shadows: widget text gets Blender’s 1 px drop shadow, and panel titles its soft 3×3 one.

FreeType is on by default (CMake BUI_TEXT_FREETYPE). With it off, stb_truetype rasterizes glyphs instead; stb_truetype also reads character maps, metrics and kerning tables in both cases.

Glyph bitmaps are cached per glyph, so text that changes every frame (a ticking number, say) stays cheap.

On the GPU: Slug

With the GPU renderer, text is drawn one quad per glyph. By default it uses Slug: glyph outlines are uploaded once as curves, and the pixel shader computes exact coverage. Text is sharp at any size, with no glyph bitmaps at all.

The alternative is a per-glyph bitmap atlas, Blender’s own approach: about half the GPU work, but bitmaps per size. Switch with BUI_SLUG=0 (or the API calls on the Rendering page).

Using other fonts

Inter covers the UI. When you ask for another family (a monospace editor, a brand font), BUI finds it in this order:

1. Fonts you registered from code, exact style first.
2. A file path: a family name ending in .ttf, .otf or .ttc loads that file.
3. BUI_FONT, if set, replaces the default face (Inter).
4. A known generic family (monospace, serif …), then a file called <family>.ttf, in the font folders below. Anything else falls back to Inter.

Font folders are searched in order: BUI_FONT_DIR first, if set, then the system’s:

If a family has no bold or italic face, BUI synthesizes one.

Register a font from code

blenderui::add_font("Brand", false, false, include_bytes!("Brand-Regular.ttf"));

/* family, style flags (BUI_FONT_BOLD | BUI_FONT_ITALIC), data, length */
BUI_text_add_font("Brand", 0, data, len);   /* returns 0 on bad data */

BUI_FONT=/path/to/Brand.ttf python my_app.py     # replaces Inter as the UI font
BUI_FONT_DIR=/path/to/fonts python my_app.py     # an extra folder to search first

Windows’ GDI text (optional)

On Windows, you can build BUI with Windows’ own GDI text engine and system fonts instead: CMake -DBUI_TEXT_GDI=ON, or the gdi-text feature in Rust. Text then uses ClearType-style hinting and Windows’ fonts, and the GPU renderer can’t use Slug. Most apps should keep the default, which looks like Blender everywhere.

Limits worth knowing

• No per-glyph font fallback. Characters that Inter (or the chosen face) doesn’t have show as boxes. A family list in CSS picks one face per element; it doesn’t mix faces within a line.
• No IME. Input methods for Chinese, Japanese and Korean aren’t supported yet.
• Right-to-left text is reordered (bidi) but not shaped, so Arabic letters don’t join.
• No OpenType features (font-feature-settings and friends): the text engine doesn’t shape, and Blender’s doesn’t either.
• Rust only: text doesn’t wrap around floats, and text-align: justify aligns left.

Troubleshooting

Next steps