Introduction

fastanim is a mathematical-animation engine in the spirit of manim. Scenes can be written in Rust or as Rhai scripts; this book covers the scripts.

A scene script runs once, top to bottom. It adds shapes and text to a global scene and plays animations on it. What it records is baked into a timeline, so playback, scrubbing and export never run the script again.

// A circle draws itself, then a formula is written under it.
// fastanim preview hello.rhai

let title = scene.add(text("Hello, fastanim").to_edge(UP));
scene.play(write(title));

let ring = scene.add(circle(1.5).stroke(BLUE, 0.06));
scene.play(create(ring).run_time(1.5));

let formula = scene.add(math_tex("y = sin(x)").scale(1.5).fill(GREEN).to_edge(DOWN));
scene.play(write(formula));
scene.wait(1.0);

Save that as hello.rhai and run fastanim preview hello.rhai. The window re-bakes the scene every time you save the file.

Install

Prebuilt binaries are attached to each GitHub release. With cargo-binstall:

cargo binstall --git https://github.com/simonhdickson/fastanim fastanim-cli

Or build from source (Rust 1.92+):

cargo install --locked --git https://github.com/simonhdickson/fastanim fastanim-cli

Video export also needs ffmpeg on your PATH.

Try it in the browser

The playground runs scripts in the browser with no install. It ships with the example scenes from fastanim-script/scenes. Link straight to one with ?scene=<name>, e.g. ?scene=diff, or to the first .rhai file in a public GitHub gist with ?gist=<id>. Share link copies a link that holds the script itself, so edits can be shared with nothing uploaded anywhere.