line-art-animation

A Claude skill and a small TypeScript library for animated line-art components: ink-on-paper figures that walk, ride and react, in scenes that run from day to night. Everything is drawn live in SVG, so it stays sharp at any size and responds to the pointer.

Day	Night

What's in the repo

Install the skill

For Claude Code, clone it into your skills folder:

git clone https://github.com/JDhruv14/line-art-animation ~/.claude/skills/line-art-animation

or into .claude/skills/ inside a single project. Then ask for what you want, for example:

• "Make a line art animation of a bakery at dawn: a baker carrying trays, steam from the oven, a cat in the window."
• "Turn this clip into a looping line-art component, matching its walk exactly." (attach or link the clip)
• "Add a day-night cycle to the scene and render a 30-second 1080p video."

Claude reads SKILL.md, copies lib/ into your project, shows one figure for approval before building the rest, and checks motion frame by frame before handing it over.

Run the examples

Requires Node 22.18 or newer.

npm install
npm run dev        # http://localhost:5173

In the village, drag the sun or moon across the sky to change the time, move the pointer to make wind, and click people, windows, lanterns, the wind chime, the cat, the birds or the water. URL flags: ?start=0.9 sets the starting time (0 is midnight, 0.5 noon), ?tau=0.5 pins it, ?day=30 makes a full day last 30 seconds, ?debug steps time by hand.

npm run typecheck  # strict for lib/ and the walker
npm run build

The library in brief

Figures are drawn in their own space, about 95 units tall with feet on y = 120, and placed into a scene with a transform. Limbs are two open pen strokes around a curve through the joints, which is most of what makes the drawing read as hand-inked.

A complete program that draws a pair of legs walking across the page (the walker example adds the body, arms, clothes and the click reaction):

import { el, limb, shoe, place, inkDefs, run } from './lib/ink.ts';
import { gait } from './lib/gait.ts';

const svg = el('svg', { viewBox: '0 0 480 240' });
document.body.append(svg);
const fig = el('g', { filter: inkDefs(svg).filter }, svg);
const legs = [limb(fig, 4.2), limb(fig, 4.2)];
const shoes = [el('path', {}, fig), el('path', {}, fig)];

const walk = gait({ kind: 'walk' });
let phase = 0, x = 60;
run((t, dt) => {
  phase += dt / walk.period;
  x += walk.speed * 1.25 * dt;           // move at the gait's speed and the feet stay planted
  place(fig, x % 520 - 20, 196, 1, 1.25);
  const p = walk.pose(phase);
  p.feet.forEach((foot, i) => {
    legs[i].draw([p.hip, foot.knee, foot.ankle]);
    shoe(shoes[i], foot.ankle, foot.pitch);
  });
});

gait() solves the legs rather than animating them: the planted foot slides back at exactly the travel speed, the swing follows a minimum-jerk path, the heel peels off the toe before each step, and hip height comes from what the planted legs can reach, so the body rises over each step and dips when both feet are down. Clothes are then drawn around the knees and ankles, so a coat or kimono opens and closes with the stride.

palette(τ) gives sky, paper and ink colours for any time of day. Ink is currentColor and paper fills carry a pp class, so applyPalette() can turn the whole drawing into pale ink on indigo at night while windows and lanterns glow.

Render a video

npm run dev
node scripts/capture.ts "http://localhost:5173/examples/village/?debug&capture&day=30&start=0.3" \
  captures/village 900 30 1920 1080
ffmpeg -framerate 30 -i captures/village/f%04d.png -c:v libx264 -preset slow -crf 15 \
  -pix_fmt yuv420p -movflags +faststart -tune animation village.mp4

The capture script drives headless Chrome over the DevTools protocol, with no npm dependencies, and advances the scene by exactly one frame between screenshots, so the result doesn't depend on machine speed. It finds a local Chrome or Chromium, or uses $CHROME. Needs ffmpeg.

Match a reference clip

node scripts/clip.ts period clip.mp4 X Y W H          # loop length of a region
node scripts/clip.ts blobs clip.mp4 X Y W H Y0 Y1     # dark blobs per frame, e.g. feet
scripts/frames.sh clip.mp4 X Y W H out/               # frames with a measuring grid

references/matching.md covers the rest: why to resample by time (most social clips are variable-frame-rate), reading poses off the grid, and an overlay mode for checking your drawing against the clip.

License

MIT