KAS GUI

KAS is a widget-first GUI toolkit:

• widgets retain state
• flexibile drawing, layout, event handling, animation
• clean, type-safe widget interaction
• full keyboard control of UI
• fast, efficient, responsive

Features

• Good automatic layout (margins, text wrapping width-for-height logic)
• Partially declarative UI descriptions possible through macros
• Advanced text features: shaping, bidirectional support, font fallbacks
• Embedded GPU shaders (see Mandlebrot example)
• Supports theming and end-user configuration
• View widgets for seemless scrolling and sharing of large data
• Stepless DPI scaling:

Limitations

• Slow compile times. See Faster builds.
• Somewhat large binaries; e.g. for the gallery example: 333M (debug), 38M (debug + strip), 20M (release), 12M (release + strip). Note that these binaries are statically linked, as is the norm for Rust. Some improvements may be possible, e.g. disabling features such as shaping and image or replacing the rendering backend.

Documentation

• Wiki: Getting started, Configuration, Troubleshooting
• API docs: https://docs.rs/kas, https://docs.rs/kas-core, https://docs.rs/kas-widgets, https://docs.rs/kas-theme, https://docs.rs/kas-wgpu
• KAS Tutorials
• Changlelog
• Roadmap
• Discuss
• KAS Blog

Examples

See the examples directory and kas-gui/7guis.

Precompiled example apps can be downloaded as follows:

• go to https://github.com/kas-gui/kas/actions/workflows/build.yml
• select the latest (complete) run
• download one of the examples-* artifacts

Design

Data or widget first?

KAS uses a widget-first design: widgets are persistent and retain state; data must be pushed into widgets. Many modern UIs are data-first: widgets are built per-frame over a single persistent data object. There are significant trade-offs of a widget-first design:

• (for) widgets have embedded state; data-first designs may require explicitly connecting widgets to state, for those that need it
• (against) dynamic layout is harder
• (for) updates are fast since only affected widgets need be touched; using 10,000+ widgets in a UI is not a problem
• (against) rebuilding the UI is much slower
• (for) pre-built "view widgets" with built-in support for scrolling over large external databases (only retrieving visible entries)
• (against) "view widgets" are an emulation of data-first design over a widget-first model, and less flexible

Crates and features

Crates

• kas is a meta-package; most of the time this is the only one you need to use directly
• kas-macros: a helper crate for proc macros
• kas-core provides most interfaces and logic concerning widgets (event handling, layout, draw API, geometry types)
• KAS-text: provides text layout and font management
• kas-widgets: the standard widget library
• kas-theme: theming support for KAS (API, two themes, config support)
• kas-wgpu: provides windowing via winit and rendering via WGPU
• kas-dylib: support for dynamic linking
• https://docs.rs/easy-cast: spin-off crate for checked casts
• https://docs.rs/impl-tools: spin-off macro support crate

At this point in time, kas-wgpu is the only windowing/rendering implementation and kas-theme the only theme (high-level drawing) implementation, thus kas uses these crates by default, though they are optional.

Feature flags

The kas crate enables most important features by default, excepting those requiring nightly rustc. Other crates enable fewer features by defualt.

The following non-default features of kas are highlighted:

• dynamic: enable dynamic linking for kas (see Faster builds)
• internal_doc: turns on some extra documentation intended for internal usage but not for end users. (This only affects generated documentation.)
• nightly: enables the less problematic unstable features
• min_spec (enabled by nightly): use min_specialization for some visual improvements: scrolled regions are drawn under scroll bars, underlines on check-box accelerator keys show with the Alt key.
• spec: use specialization to enable TryFormat

For full documentation of feature flags, see the Cargo.toml.

Copyright and Licence

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 licence from the LICENSE file or on the following webpage: https://www.apache.org/licenses/LICENSE-2.0