# Spanda Documentation
> *Sanskrit: स्पन्द — vibration, pulse, the throb of motion.*
Welcome to the **spanda** documentation! This library is built around a single, powerful idea: **any value that can be linearly interpolated can be animated.**
Everything else — easing curves, keyframe tracks, timelines, physics springs, scroll-linked animations, and motion paths — is layered on top of that one primitive.
---
## Philosophy
Spanda is a **pure value interpolation engine**. It computes animation values mathematically; it never touches the DOM, Canvas, or any rendering target. You provide time (`dt`), spanda returns values — you render however you want.
This architecture makes spanda work **everywhere**:
- Terminal UIs (ratatui, crossterm)
- Web / WASM (Leptos, Dioxus, Yew)
- Game engines (Bevy)
- Native desktop apps
- Embedded / `no_std` environments
---
## Core Modules
| **Tween** | Animate a single value from A to B with easing, looping, callbacks | [tween.md](tween.md) |
| **Easing** | 38+ easing curves (31 standard + CSS + 5 advanced) | [easing.md](easing.md) |
| **Keyframes** | Multi-stop animation with per-segment easing | [keyframe.md](keyframe.md) |
| **Timeline & Sequence** | Compose animations concurrently or sequentially | [timeline.md](timeline.md) |
| **Spring** | Physics-based damped harmonic oscillator + generic SpringN<T> | [spring.md](spring.md) |
| **Scroll** | Scroll-linked animations with ScrollDriver/ScrollClock | [scroll.md](scroll.md) |
| **Motion Paths** | Bezier curves, CatmullRom, PolyPath, CompoundPath, SVG parser | [path.md](path.md) |
| **Colour** | 9 palette types, InLab/InOklch/InLinear colour-space wrappers | [colour.md](colour.md) |
| **DrawSVG** | Stroke-dashoffset draw-on/draw-off helpers | [v080.md](v080.md) |
| **Morph** | MorphPath point-by-point shape morphing + resample | [v080.md](v080.md) |
| **Inertia** | Friction deceleration (Inertia, InertiaN) with presets | [v080.md](v080.md) |
| **Drag** | Pure-math drag tracking with velocity, constraints, grid snap | [v080.md](v080.md) |
| **Advanced Easings** | RoughEase, SlowMo, ExpoScale, Wiggle, CustomBounce | [easing.md](easing.md) |
| **WASM-DOM Plugins** | FLIP, SplitText, ScrollSmoother, Draggable, Observer | [v080.md](v080.md) |
| **Driver & Clock** | Manage multiple animations with time abstraction | [integrations.md](integrations.md) |
| **Leptos** | Reactive signal integration guide | [leptos_guide.md](leptos_guide.md) |
| **Dioxus** | Coroutine-based animation guide | [dioxus_guide.md](dioxus_guide.md) |
| **Feature Matrix** | Which flags enable which modules | [feature_matrix.md](feature_matrix.md) |
---
## Quick Start
Add `spanda` to your `Cargo.toml`:
```toml
[dependencies]
spanda = "0.8"
```
### Basic Tween
```rust
use spanda::{Tween, Easing};
use spanda::traits::Update;
let mut tween = Tween::new(0.0_f32, 100.0)
.duration(1.0)
.easing(Easing::EaseOutCubic)
.build();
// Inside your rendering loop:
for _ in 0..10 {
tween.update(0.1);
let current = tween.value();
// render(current);
}
assert!(tween.is_complete());
assert!((tween.value() - 100.0).abs() < 1e-6);
```
### Looping Tween
```rust
use spanda::{Tween, Loop};
use spanda::traits::Update;
let mut tween = Tween::new(0.0_f32, 100.0)
.duration(1.0)
.looping(Loop::PingPong)
.build();
// Bounces between 0 and 100 forever
for _ in 0..600 {
tween.update(1.0 / 60.0);
}
```
### Spring Animation
```rust
use spanda::spring::{Spring, SpringConfig};
use spanda::traits::Update;
let mut spring = Spring::new(SpringConfig::wobbly());
spring.set_target(100.0);
// Springs have no fixed duration — they settle naturally
for _ in 0..300 {
spring.update(1.0 / 60.0);
let pos = spring.position();
// render(pos);
}
assert!(spring.is_settled());
```
### Timeline Composition
```rust
use spanda::timeline::Sequence;
use spanda::tween::Tween;
use spanda::traits::Update;
let mut timeline = Sequence::new()
.then(Tween::new(0.0_f32, 100.0).duration(0.5).build(), 0.5)
.gap(0.1)
.then(Tween::new(100.0_f32, 0.0).duration(0.3).build(), 0.3)
.build();
timeline.play();
timeline.update(0.9);
```
### Staggered Animations
```rust
use spanda::timeline::stagger;
use spanda::tween::Tween;
use spanda::traits::Update;
let tweens: Vec<_> = (0..5).map(|i| {
let end = (i + 1) as f32 * 20.0;
(Tween::new(0.0_f32, end).duration(0.5).build(), 0.5)
}).collect();
let mut timeline = stagger(tweens, 0.1);
timeline.play();
// Animations start at t=0.0, 0.1, 0.2, 0.3, 0.4
```
### Scroll-Linked Animation
```rust
use spanda::scroll::ScrollDriver;
use spanda::tween::Tween;
let mut driver = ScrollDriver::new(0.0, 1000.0);
driver.add(Tween::new(0.0_f32, 100.0).duration(1.0).build());
// Drive from scroll position instead of time
driver.set_position(500.0);
```
### Motion Path Animation
```rust
use spanda::path::{MotionPath, MotionPathTween, PathEvaluate};
use spanda::easing::Easing;
use spanda::traits::Update;
let path = MotionPath::new()
.cubic([0.0_f32, 0.0], [50.0, 100.0], [100.0, 100.0], [150.0, 0.0])
.line([150.0, 0.0], [200.0, 0.0]);
let mut tween = MotionPathTween::new(path)
.duration(2.0)
.easing(Easing::EaseInOutCubic);
tween.update(1.0);
let pos = tween.value();
```
### Colour Animation (palette feature)
```rust,ignore
use palette::Srgba;
use spanda::{Tween, Easing};
use spanda::colour::InLab;
use spanda::traits::Update;
// Interpolate in CIE L*a*b* for perceptually smooth gradients
let mut tween = Tween::new(
InLab(Srgba::new(1.0, 0.0, 0.0, 1.0)), // red
InLab(Srgba::new(0.0, 0.0, 1.0, 1.0)), // blue
)
.duration(1.0)
.easing(Easing::EaseInOutCubic)
.build();
tween.update(0.5);
let colour = tween.value().0; // Srgba
```
### Using the Animation Driver
```rust
use spanda::driver::AnimationDriver;
use spanda::tween::Tween;
use spanda::easing::Easing;
let mut driver = AnimationDriver::new();
// Add multiple animations — they're managed automatically
let id = driver.add(
Tween::new(0.0_f32, 1.0).duration(1.0).build()
);
// Tick all animations each frame
driver.tick(0.5);
assert_eq!(driver.active_count(), 1);
driver.tick(0.5);
assert_eq!(driver.active_count(), 0); // completed animations are auto-removed
```
---
## Feature Flags
| `std` | *(default)* Wall-clock driver, thread-safe `AnimationDriverArc` | TUI apps, CLI tools |
| `serde` | `Serialize`/`Deserialize` on all public types | State persistence, network sync |
| `bevy` | `SpandaPlugin` for Bevy 0.13 — auto-ticks Tween/Spring components | Game development |
| `wasm` | `RafDriver` for browser `requestAnimationFrame` | Web apps (Leptos/Dioxus/Yew) |
| `wasm-dom` | DOM plugins: FLIP, SplitText, ScrollSmoother, Draggable, Observer | Web apps with DOM interaction |
| `palette` | Colour interpolation via the `palette` crate | Smooth colour animations |
| `tokio` | `async`/`.await` on timeline completion | Async workflows |
### Feature Flag Decision Guide
| A TUI app | `default` (just `std`) |
| A Bevy game | `bevy` |
| A WASM web app | `wasm` |
| A WASM app with DOM plugins | `wasm-dom` |
| A CLI tool | `default` |
| Embedded / `no_std` | `default-features = false` |
| Full everything | `std,serde,bevy,wasm,wasm-dom,palette,tokio` |
---
## Architecture Overview
```
┌──────────────────────────────────────────────┐
│ Your Application │
│ (TUI / Bevy / Leptos / Desktop / CLI) │
└──────────────────────┬───────────────────────┘
│ reads value()
┌──────────────────────▼───────────────────────┐
│ AnimationDriver / ScrollDriver │
│ manages multiple active animations, │
│ auto-removes completed ones │
└──────────────────────┬───────────────────────┘
│ .tick(dt) / .set_position(pos)
┌──────────────┼──────────────┬──────────────┐
▼ ▼ ▼ ▼
┌─────────┐ ┌──────────┐ ┌──────────┐ ┌────────────┐
│ Tween<T>│ │ Keyframe │ │ Spring │ │MotionPath │
│ │ │ Track<T> │ │ Inertia │ │ Tween │
└─────────┘ └──────────┘ └──────────┘ └────────────┘
│ │ │ │
▼ ▼ ▼ ▼
┌──────────────────────────────────────────────────────┐
│ Interpolate / Animatable │
│ (f32, f64, [f32;2..4], i32, palette colours) │
└──────────────────────────────────────────────────────┘
│ │
▼ ▼
┌─────────────┐ ┌──────────────┐
│ MorphPath │ │ DragState │
│ DrawSVG │ │ → InertiaN │
└─────────────┘ └──────────────┘
```
### Data Flow
1. **Clock** produces `dt` (seconds since last frame) — or `ScrollClock` produces dt from scroll position
2. **AnimationDriver** / **ScrollDriver** calls `update(dt)` on every active animation
3. Each animation (**Tween**, **KeyframeTrack**, **Spring**, **MotionPathTween**) advances its internal state
4. Your app reads `.value()` / `.position()` and renders
---
## Type System
The trait hierarchy is minimal and powerful:
```
Interpolate — lerp(&self, other: &Self, t: f32) -> Self
└── Animatable — Interpolate + Clone + 'static (blanket impl)
└── Used as bounds on: Tween<T>, KeyframeTrack<T>
PathEvaluate<T> — evaluate(&self, t: f32) -> T
└── Implemented by: BezierPath<T>, MotionPath<T>
Update — update(&mut self, dt: f32) -> bool
└── Implemented by: Tween, KeyframeTrack, Timeline, Spring, MotionPathTween
```
To animate your own type, just implement `Interpolate`:
```rust
use spanda::traits::Interpolate;
#[derive(Clone)]
struct Color { r: f32, g: f32, b: f32 }
impl Interpolate for Color {
fn lerp(&self, other: &Self, t: f32) -> Self {
Color {
r: self.r + (other.r - self.r) * t,
g: self.g + (other.g - self.g) * t,
b: self.b + (other.b - self.b) * t,
}
}
}
// Now you can do: Tween::new(red, blue).duration(1.0).build()
```
---
## Project Structure
```
src/
├── lib.rs — crate root, re-exports
├── traits.rs — Interpolate, Animatable, Update
├── easing.rs — 38 easing functions + CubicBezier + Steps + 5 advanced
├── tween.rs — Tween<T>, TweenBuilder, TweenState
├── keyframe.rs — KeyframeTrack, Keyframe, Loop
├── timeline.rs — Timeline, Sequence, At, stagger
├── spring.rs — Spring, SpringConfig, SpringN<T>, SpringAnimatable
├── clock.rs — Clock trait, WallClock, ManualClock, MockClock
├── driver.rs — AnimationDriver, AnimationDriverArc, AnimationId
├── scroll.rs — ScrollClock, ScrollDriver
├── path.rs — BezierPath, MotionPath, MotionPathTween
├── bezier.rs — CatmullRomSpline, PathEvaluate2D
├── motion_path.rs — PolyPath, CompoundPath, PathCommand
├── svg_path.rs — SvgPathParser (SVG d-attribute parser)
├── colour.rs — colour interpolation (feature = "palette")
├── svg_draw.rs — DrawSVG stroke-dashoffset helpers
├── morph.rs — MorphPath shape morphing + resample
├── inertia.rs — Inertia, InertiaN friction deceleration
├── drag.rs — DragState, DragConstraints, PointerData
└── integrations/
├── mod.rs
├── bevy.rs — SpandaPlugin (feature = "bevy")
├── wasm.rs — RafDriver (feature = "wasm")
├── split_text.rs — SplitText character/word splitting
├── flip.rs — FlipState, FlipAnimation (feature = "wasm-dom")
├── scroll_smoother.rs — ScrollSmoother (feature = "wasm-dom")
├── draggable.rs — Draggable DOM binding (feature = "wasm-dom")
└── observer.rs — Observer unified input (feature = "wasm-dom")
```
---
## Integrations
See the full [Integrations Guide](integrations.md) for:
- **Bevy** — `SpandaPlugin` auto-ticks components
- **WASM** — `RafDriver` for browser `requestAnimationFrame`
- **TUI/CLI** — `WallClock` + render loop
- **Leptos/Dioxus** — WASM driver patterns, `on_update` callback bridge
- **Scroll-linked** — `ScrollDriver` for position-driven animations
- **Embedded / `no_std`** — zero dependency math-only mode
---
## Contributing
Contributions are welcome! Please:
1. Fork the repository
2. Create a feature branch
3. Run `cargo test && cargo clippy --all-features -- -D warnings`
4. Submit a pull request
---
## License
Licensed under either of
- [Apache License, Version 2.0](../LICENSE-APACHE)
- [MIT License](../LICENSE-MIT)
at your option.