Environment, input, and input method editor
This page covers the public contracts that connect the shared runtime to user input and host-provided context.
The two main ideas are simple.
Env carries explicit environment values that widgets may need while building.
InputEvent carries normalized user and lifecycle input that the runtime can process consistently across platforms.
The clipboard and input method editor contracts sit beside those two types because they are part of the same shell-to-runtime boundary.
Env
Env is the read-only environment bundle exposed to widgets through ViewHandle.
Today, the public fields include:
Field | Meaning | Typical use |
|---|---|---|
theme | The active visual theme | Component styling and token lookup |
i18n | The loaded internationalization registry | Translated text lookup |
locale | The currently active locale | Translation and locale-sensitive presentation |
window_insets | Host-reported insets such as safe-area style boundaries | Mobile-safe layout and edge-aware content |
viewport_size | The current logical viewport size | Responsive layout decisions |
measurer | Optional text measurement backend | Text layout and shaping support |
Use Env for shared presentation and host-context values, not for durable product state.
A widget should read environment through ViewHandle, for example with view.viewport_size(), view.theme(), or view.env.locale.
How Env reaches the app
Desktop currently exposes public with_env(...) and with_sync_env(...) builders. Mobile and web expose public with_sync_env(...). SSR apps expose with_env(...) and with_request_env(...); Static site targets expose with_env(...).
Use with_env(...) when you want to seed a prepared environment, such as an environment that already contains translation bundles.
Use with_sync_env(...) when values in GlobalState should be mirrored into Env, such as a user-selected locale or theme mode.
Use with_request_env(...) on server-rendered apps when request data should select presentation context before rendering, such as a locale stored in a route prefix, header, cookie, or session.
The important contract is that environment remains explicit and shell-managed, not hidden behind global process state.
InputEvent
InputEvent is the top-level normalized input type consumed by the runtime.
It exists so the shared core can reason about input consistently even though each shell starts from different native APIs.
The public variants are:
Variant | Meaning |
|---|---|
Pointer(PointerEvent) | Mouse, touch, or stylus input |
Keyboard(KeyEvent) | Key presses and releases |
Ime(ImeEvent) | Composed-text events from an input method editor |
Gesture(GestureEvent) | Higher-level gestures such as taps or pans |
Lifecycle(LifecycleEvent) | App or surface lifecycle events such as init or resize |
This normalization is a major reason cross-platform behavior stays consistent and testable.
Pointer and keyboard details
PointerEvent covers pointer down, up, move, and scroll. Pointer buttons are represented by PointerButton.
KeyEvent covers key down and key up. Key identity is represented by KeyCode, and modifier bits use constants such as MOD_SHIFT, MOD_ALT, MOD_CTRL, and MOD_SUPER.
Use these contracts when you are building custom input-aware widgets or investigating runtime input flow. Most ordinary app code benefits from them indirectly through built-in widgets.
Input method editor, in reference terms
An input method editor is the system used for composed text entry. This is essential for many writing systems and also matters for accents, emoji, and other non-trivial text entry flows.
The public input method editor event type is ImeEvent, with these variants:
Variant | Meaning |
|---|---|
Preedit { text } | Temporary composed text that is still being edited |
Commit { text } | Final text confirmed by the user |
This contract exists so text-heavy widgets can handle real composition instead of pretending every character arrives as final committed text immediately.
Clipboard and input method editor shell traits
Fission does not hide clipboard and input method editor support inside one desktop-only implementation detail. The core runtime exposes public shell-facing traits for both.
Trait | Purpose |
|---|---|
Clipboard | Text clipboard access through get_text() and set_text() |
ImeHandler | Shell control over input method editor allowed state and cursor-area updates |
Shells provide the real platform implementations. Tests can provide mocks.
That separation matters because clipboard and input method editor behavior are part of the host boundary, but they still need to plug into the shared runtime model explicitly.
Related runtime-owned text state
This page is about the public boundary types, but it helps to remember that the runtime also owns text-edit state internally. That includes caret and selection state, undo history, preedit state, and other editing affordances.
That ownership is why built-in TextInput and more advanced text surfaces can share the same underlying model instead of each inventing their own text pipeline.
Related reference pages
For theme and locale flow specifically, continue to Theming and internationalization. For the higher-level teaching guide that explains how these contracts feel in real app code, see Input, text, and environment.
Fission
A cross-platform, GPU-accelerated user interface framework for Rust. MIT licensed.
Copyright (c) 2026 Fission
Ready to use today. Widget APIs are expected to remain stable; some runtime and shell APIs may change before 1.0.0.
Fission 0.7.0