/svg-animation

name: svg-animation
description: This skill should be used when the user asks to "animate an SVG", "make a line draw itself on", "do a stroke draw-on / signature animation", "morph one shape into another", "move an element along a path", "animate an icon/logo", or "animate an SVG gradient or filter". Covers stroke-dashoffset draw-on, path morphing, motion-along-path, and animated icons/gradients/filters via CSS, SMIL, and GSAP.
version: 0.1.0

SVG Animation

Crisp, lightweight, infinitely scalable vector motion — ideal for icons, illustrations, logos, and data marks. SVG can be animated three ways: CSS (declarative, simple), SMIL (`<animate>` inside the SVG), and JS (GSAP/Web Animations, for control and morphing). Choose per task; the techniques below say which.

When to use

• Stroke "draw-on" of icons, illustrations, signatures, maps
• Shape/path morphing and animated icon state changes (menu ↔ close, play ↔ pause)
• Moving an element along a path (motion path)
• Animated gradients, filters (glow, displacement), and animated logos

Core techniques

Stroke draw-on (the staple)

Draw the dash array as long as the path, offset it fully (invisible), then animate the offset to 0.

.path {
  stroke-dasharray: var(--len);
  stroke-dashoffset: var(--len);
  animation: draw 1.4s ease forwards;
}
@keyframes draw { to { stroke-dashoffset: 0; } }

Getting the length:

• JS (most reliable): `const len = path.getTotalLength(); path.style.setProperty("--len", len);`
• No-JS trick: set `pathLength="1"` on the `<path>`, then `stroke-dasharray: 1; stroke-dashoffset: 1;` and animate to `0`. This normalizes any path to a 0–1 length so no measurement is needed.

Reverse (erase) by animating offset from 0 back to `len`. Stagger multiple paths with `animation-delay`. Direction of drawing follows the path's point order; reverse it in the editor or negate the offset sign if it draws "backwards".

Morphing one path into another

Paths interpolate point-by-point, so a naive morph requires both `d` attributes to have the **same number and type of commands**. Two robust approaches:

• **GSAP MorphSVG** (free as of GSAP 3.12) — handles mismatched point counts automatically and finds a good mapping:

gsap.registerPlugin(MorphSVGPlugin);
gsap.to("#start", { morphSVG: "#end", duration: 0.8, ease: "power2.inOut" });
// Convert any shape to a morph-able path:
MorphSVGPlugin.convertToPath("circle, rect, ellipse, line, polygon");

• **Flubber** (small standalone lib) — generates interpolators without GSAP, good with React/Framer Motion:

import { interpolate } from "flubber";
const interpolator = interpolate(pathA, pathB, { maxSegmentLength: 2 });
// interpolator(0) === pathA, interpolator(1) === pathB; feed t into a tween.

For hand-authored morphs (icon toggles), keep both paths with identical command structure and animate `d` directly via Web Animations or CSS (`d` is animatable in modern browsers via `path("...")`).

Motion along a path

• **GSAP MotionPath** (preferred — control, alignment, scrub):

gsap.registerPlugin(MotionPathPlugin);
gsap.to("#rocket", {
  duration: 4, repeat: -1, ease: "none",
  motionPath: { path: "#track", align: "#track", autoRotate: true, alignOrigin: [0.5, 0.5] },
});

`autoRotate: true` orients the object to the path tangent; `align` makes coordinates relative to the path element.

• **SMIL** (no JS):

<path id="track" d="M10,80 C40,10 120,10 150,80" fill="none"/>
<circle r="6" fill="#3b82f6">
  <animateMotion dur="3s" repeatCount="indefinite" rotate="auto">
    <mpath href="#track"/>
  </animateMotion>
</circle>

• **CSS** offset-path (modern, declarative): `offset-path: path("M10,80 C..."); animation: move 3s linear infinite;` with `@keyframes move { to { offset-distance: 100%; } }` and `offset-rotate: auto`.

Animated gradients and filters

Gradients: animate `gradientTransform` or stop offsets. A sheen sweep:

<linearGradient id="sheen">
  <stop offset="0%"  stop-color="#fff" stop-opacity="0"/>
  <stop offset="50%" stop-color="#fff" stop-opacity=".8"/>
  <stop offset="100%" stop-color="#fff" stop-opacity="0"/>
  <animateTransform attributeName="gradientTransform" type="translate"
    from="-1 0" to="1 0" dur="2s" repeatCount="indefinite"/>
</linearGradient>

Filters: animate `feDisplacementMap` `scale` for gooey/wobble, `feGaussianBlur` `stdDeviation` for focus pulls, or `feColorMatrix`/`feFlood` for glow. Filters are paint-heavy — animate sparingly and prefer `transform`/`opacity` where possible.

Implementation choice (pick fast)

| Need | Use | |------|-----| | Single declarative draw/fade | CSS | | Self-contained, no JS bundle | SMIL (`<animate*>` in the SVG) | | Coordinated, scrubbable, scroll-tied | GSAP | | Mismatched-point morph | GSAP MorphSVG or Flubber | | Path following with rotation | GSAP MotionPath / CSS offset-path |

SMIL caveat: not supported in IE/old Edge and historically deprecation-flagged; for max reach or scroll-syncing, prefer CSS or JS. SMIL is still fine for self-contained icon assets in evergreen browsers.

Authoring and optimization

• Build/clean with **SVGO**: keep `viewBox`, drop editor metadata, but disable `cleanupIds`/`removeViewBox` and any plugin that renames IDs you reference from CSS/JS/SMIL. Disable `mergePaths` and `convertShapeToPath` if you animate individual sub-paths or shapes.
• Inline the SVG in the DOM (not `<img src>`) so CSS/JS can reach its internals; `<img>`-embedded SVG can only self-animate via internal SMIL/CSS.
• Set explicit `viewBox` and avoid fixed `width`/`height` so the asset scales fluidly.
• For draw-on, ensure paths are actual strokes (`fill:none; stroke:...`), not filled outlines — dashoffset only affects strokes.
• Respect `prefers-reduced-motion`: gate looping/large motion; keep a static final state.

Deliver & verify (standalone HTML)

> **Packaged helper** (`scripts/`): `scripts/seek-shot.sh anim.html 0 1.5 3` freeze