Public API

twill keeps its public API centered on style primitives and backend adapters.

If you only need the backend-agnostic style engine, depend on twill-core directly. The top-level twill crate is now a facade that re-exports the same core modules and optionally adds GUI adapters.

Core entry points

• Style
• twill-core
• twill::prelude::core::*
• twill::prelude::theme::*
• twill::prelude::arbitrary::*
• twill::prelude::traits::*
• twill::prelude::*
• Merge
• ComputeValue
• Responsive

Tokens

Main token families:

• Color, ColorFamily, Scale, ColorValue
• BackgroundColor, TextColor, BorderColor, OutlineColor, RingColor
• ColorValueToken and *ColorVar wrappers for typed arbitrary/custom-property values
• SemanticColor, SemanticThemeVars, DynamicSemanticTheme
• ThemeVariant
• Spacing, Percentage, Container, Breakpoint
• FontFamily, FontSize, FontWeight, LetterSpacing, LineHeight
• BorderRadius, BorderWidth, BorderStyle, OutlineStyle, RingWidth
• Shadow, InsetShadow, DropShadow, TextShadow
• AnimationToken, TransitionDuration, TransitionProperty, Easing

Utilities

Common utility-style value types:

• Padding, PaddingValue, PaddingVar
• Margin, MarginValue, MarginVar
• Width, WidthVar
• Height, HeightVar
• SizeConstraints
• Display, Position, Overflow, ZIndex
• FlexContainer, FlexDirection, Flex
• GridContainer, GridTemplate

Recommended usage

#![allow(unused)]
fn main() {
use twill::prelude::core::*;

let card = Style::card()
    .merged(Style::interactive())
    .padding(Padding::all(Spacing::S4))
    .hover(|style| style.shadow(Shadow::Md))
    .at_lg(|style| style.padding(Padding::all(Spacing::S6)));

assert!(!card.is_empty());
}

Composition helpers

Prefer composing Style values instead of creating framework-specific wrapper types:

• Style::surface() for structural spacing, radius, and elevation
• Style::card() for semantic card/background/border defaults
• Style::interactive() for pointer/focus/disabled affordances
• Style::merged(...) when you want an immutable composition step
• Style::merge_in_place(...) when you want to extend a mutable style value
• Style::resolved_theme(...) plus resolved_light_theme(...) / resolved_dark_theme(...) when you want semantic aliases converted into concrete color tokens
• Style::resolve_theme_in_place(...) when you want that resolution on a mutable style
• Verbose builder aliases like background_color(...), border_color(...), outline_color(...), ring_width(...), ring_color(...), and box_shadow(...) when you want a more self-explanatory Rust-first call site

The wide twill::prelude::* remains available, but prelude::core::* plus opt-in sub-preludes gives better IDE discoverability and smaller import scope.

Backend surface

Feature-gated backend modules:

• twill::backends::egui
• twill::backends::iced
• twill::backends::slint
• twill::egui
• twill::iced
• twill::slint

These modules convert Twill values into framework-specific primitives. Twill itself does not define components like Button or Card.

If you do not want the facade crate, use the dedicated adapter crates directly:

• twill-egui
• twill-iced
• twill-slint

Backend-specific helper types:

• twill::backends::ShadowColor
• twill::iced::TextDirection
• twill::slint::SlintCursor