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KAS Text

A pure-Rust rich-text processing library suitable for KAS and other GUI tools.

What it does (or may in the future) do:

• Font discovery (very limited; system configuration is ignored)
• Font fallback for missing glyphs
• Text layout: yield a sequence of positioned glyphs
• Supports bi-directional text
• Text shaping (optional) via rustybuzz or harfbuzz
• Handle combining diacritics correctly
• Support position navigation / lookup
• Sub-ligature navigation
• Visual-order BIDI text navigation
• Emoticons
• Rich text: choose font by style/weight/family for a sub-range
• Text annotations: highlight range, underline
• Raster glyphs (via ab_glyph or fontdue)
• Fast-ish: good enough for snappy GUIs; further optimisation possible

What it does not do:

• Draw: rastering glyphs yields a sequence of sprites. Caching these in a glyph atlas and rendering to a texture is beyond the scope of this project since it is dependent on the graphics libraries used.
• Editing: mapping input actions (e.g. from a winit WindowEvent) to text edit operations is beyond the scope of this project. The API does cover replacing text ranges and finding the nearest glyph index to a coordinate.
• Rich text: there is no packaged format for rich text. A FormattableText trait and a (limited) Markdown processor are included.
• Full text layout: there is no support for custom inter-paragraph gaps, inter-line gaps, embedded images, or horizontal rules.

For more, see the initial design document and issue #1.

Examples

Since kas-text only concerns text-layout, all examples here are courtesy of KAS GUI. See the examples directory.

Alternatives

Pure-Rust alternatives for typesetting and rendering text:

• Swash: font introspection, shaping, character and script analysis, rendering
• fontdue: rastering and simple layout
• glyph_brush: rendering and simple layout

Non-pure-Rust alternatives include font-kit and piet among others.

Contributing

Contributions are welcome. For the less straightforward contributions it is advisable to discuss in an issue before creating a pull-request.

Testing is currently done in a very ad-hoc manner via KAS examples. This is facilitated by tying KAS commits to kas-text commit hashes during development and allows testing editing as well as display. A comprehensive test framework must consider a huge number of cases and the test framework alone would constitute considerably more work than building this library, so for now user-testing and bug reports will have to suffice.

Copyright and License

The COPYRIGHT file includes a list of contributors who claim copyright on this project. This list may be incomplete; new contributors may optionally add themselves to this list.

The KAS library is published under the terms of the Apache License, Version 2.0. You may obtain a copy of this license from the LICENSE file or on the following web page: https://www.apache.org/licenses/LICENSE-2.0