zest-core

zest-core is the foundation crate for the zest GUI framework family.

It defines the application contract, the async runtime, the platform abstraction, the widget trait, event types, layout primitives, scrolling types, focus state, and dirty-region rendering support.

The crate is no_std outside tests and uses alloc.

Main pieces

Application model

The application surface is built around:

• Application
• Task
• Subscription
• Recipe
• ScreenView
• Runtime

Application::init() constructs the initial application state and startup task. Application::update(...) processes messages. Application::view() returns the active screen.

Platform model

Backends implement Platform, which provides:

• next_event()
• render_with(...)
• render_with_dirty(...)
• viewport()
• capabilities()

Rendering uses a Renderer abstraction, and backends can expose PlatformCapabilities to tell the runtime whether clipping and partial flush are supported.

Widget model

zest-core defines the object-safe Widget<C, M> trait and the boxed Element wrapper used to build heterogeneous trees.

The widget contract includes:

• measurement and arrangement
• touch handling
• semantic action routing
• focus participation
• drawing

Input and actions

The core event surface includes:

• InputEvent
• TouchEvent / TouchPhase
• KeyEvent / Key
• EncoderEvent
• UiAction

The runtime also exposes focus-related types:

• WidgetId
• FocusState
• FocusDirection

Layout, scrolling, and dirty regions

The crate exports shared layout and interaction primitives:

• Constraints
• Length
• Horizontal
• Vertical
• UNBOUNDED
• ScrollState
• ScrollMsg
• ScrollDirection
• ScrollbarMode
• SnapMode
• GesturePhase
• tick_task(...)
• DirtyRegion
• PlatformCapabilities

Running an application

Applications are driven by Runtime::<A>::new().run(platform).await.

use zest_core::Runtime;

// Runtime::<App>::new().run(platform).await;
let _runtime = Runtime::<YourApp>::new();

Runtime::run(...) rebuilds the current screen, arranges the widget tree, synchronizes focus and pressed state, waits on platform input / pending tasks / subscriptions, and redraws as needed.

Renderer helpers

The crate exports:

• Renderer
• DrawTargetRenderer
• RenderError
• arc_sin_cos(...)

These are the pieces both widgets and backends use to draw into a target.

When to use zest-core

Use this crate directly when you are:

• writing a custom Platform
• building widgets outside zest-widget
• integrating the runtime with your own hardware backend
• working with the framework without the top-level convenience crate