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Twill

Idiomatic Rust styling library inspired by Tailwind CSS
Type-safe, composable styles for native GUI applications

What Twill Is

Twill is a backend-agnostic style system for Rust UI code. It provides:

• typed design tokens for color, spacing, typography, shadows, motion, and semantic theme aliases;
• a fluent Style builder for utility-style composition;
• typed arbitrary/custom-property escape hatches for key utility families, inspired by Tailwind's arbitrary values;
• state/style layers such as hover, focus, focus_visible, selected, checked, open, closed, data_*, and aria_*;
• breakpoint-based responsive composition via sm, md, lg, xl, and s2xl;
• backend adapters for egui, iced, and slint.

Twill does not ship UI components such as Button, Card, or Dialog, and it does not expose a CSS serialization layer.

The ecosystem now has five entry points:

• twill-core for libraries and applications that only need the backend-agnostic style engine;
• twill-egui for egui-only adapter code on top of twill-core;
• twill-iced for iced-only adapter code on top of twill-core;
• twill-slint for slint-only adapter code on top of twill-core;
• twill as the facade crate that re-exports twill-core and optionally adds GUI adapters.

Examples and cookbook pages in main target the 0.3.x API only. Legacy demos built around component APIs or CSS serialization belong to the 0.2.x release line, not this branch.

Installation

[dependencies]
twill-core = "0.3"
twill-egui = "0.3"
twill-iced = "0.3"
twill-slint = "0.3"

# or use the facade crate
twill = "0.3"

# Optional backend adapters
twill = { version = "0.3", features = ["egui"] }
twill = { version = "0.3", features = ["iced"] }
twill = { version = "0.3", features = ["slint"] }

MSRV: Rust 1.93.

Backend notes:

• twill-core is synchronous and backend-agnostic.
• twill-egui, twill-iced, and twill-slint are thin adapter crates that depend on twill-core directly.
• twill re-exports the full core API and only pulls GUI dependencies when you enable a backend feature.
• egui adds conversion helpers for egui types only.
• iced adds the Iced adapter and the Unix windowing/runtime feature set used by this crate configuration.
• slint adds Slint conversion helpers only when requested.

Quick Start

use twill::prelude::core::*;

let style = Style::card()
    .merged(Style::interactive())
    .padding(Padding::symmetric(Spacing::S2, Spacing::S4))
    .hover(|style| style.opacity(0.9))
    .data_attr(DataState::Open, |style| style.shadow(Shadow::Lg))
    .at_md(|style| style.padding(Padding::all(Spacing::S6)));

Prelude Layers

Twill now has a stratified import surface:

• twill::prelude::core::* for day-to-day Style, tokens, layout, and state builders;
• twill::prelude::theme::* for semantic aliases such as SemanticColor and theme resolvers;
• twill::prelude::arbitrary::* for typed arbitrary/custom-property escape hatches;
• twill::prelude::traits::* for generic integration traits like Merge and Responsive.

twill::prelude::* still exists when you explicitly want the full power-user surface.

Typed escape hatches stay in the style layer:

use twill::prelude::{arbitrary::*, core::*};

let style = Style::new()
    .text_color_arbitrary(ColorValueToken::from_rgb8(248, 250, 252))
    .px_var(PaddingVar::new("--panel-pad-x"))
    .pb_rem(1.25)
    .border_color_var(BorderColorVar::new("--panel-border"))
    .min_w_var(WidthVar::new("--panel-min-w"))
    .tracking_em(0.035)
    .leading_number(1.75)
    .transition_custom("filter, transform")
    .transition_duration_ms(240);

Compositional Presets

The core crate now ships a few reusable presets that stay intentionally small:

• Style::surface() for structural spacing, radius, and elevation;
• Style::card() for semantic card/background/border defaults;
• Style::interactive() for cursor, transition, focus ring, and disabled affordances.

Use them as building blocks and layer app-specific details with merged(...) or merge_in_place(...).

Core API

• Style is the central style composition type.
• twill-core is the lightest dependency when you do not need backend adapters.
• twill-egui, twill-iced, and twill-slint are the narrowest way to depend on one backend adapter.
• twill::prelude::core::* is the recommended starter import.
• twill::prelude::{theme::*, arbitrary::*, traits::*} expand the API surface only when needed.
• SemanticThemeVars and DynamicSemanticTheme provide semantic alias mapping inspired by shadcn theme variables.
• Style::resolved_theme(...), resolved_light_theme(...), and resolved_dark_theme(...) let you turn semantic aliases into concrete color tokens before backend conversion.
• twill::backends::{egui, iced, slint} expose typed conversion helpers for each supported runtime.

State And Responsive Composition

Common state layers:

• hover
• focus
• focus_visible
• active
• disabled
• selected
• checked
• open
• closed
• data_attr(DataState::..., ...)
• aria_attr(AriaAttr::..., ...)

Responsive layers:

• sm
• md
• lg
• xl
• s2xl
• Style::at_breakpoint(...)

Backends

Supported adapters:

• egui
• iced
• slint

Each backend translates Twill tokens and Style values into framework-specific primitives without changing the core style model. Use twill-egui, twill-iced, or twill-slint directly when you want one adapter crate; use twill when you want the facade and feature-gated re-exports.

Documentation

• mdBook sources live in docs/
• crate documentation is published on docs.rs/twill
• release notes live in CHANGELOG.md

Development

Useful checks:

cargo fmt --all --check
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features
cargo check --workspace --all-features --examples

License

MIT License — see LICENSE