Motion Design Principles

Three-Tier Animation Decision Tree

Choose the SIMPLEST tier that achieves the effect. Never escalate without reason.

Tier 1: CSS Scroll-Driven Animations

Use when: Simple reveals, hover effects, viewport-triggered fades. Technology: CSS animation-timeline: scroll(), @keyframes, transition. Advantages: Zero JS, best performance, compositor-only.

/* Tier 1 example: simple fade-up on scroll */
@keyframes fade-up {
  from { opacity: 0; transform: translateY(var(--motion-reveal-distance, 40px)); }
  to { opacity: 1; transform: translateY(0); }
}

.reveal-on-scroll {
  animation: fade-up linear both;
  animation-timeline: view();
  animation-range: entry 0% entry 30%;
}

Decision: If a simple CSS scroll-driven animation achieves the effect, STOP HERE.

Tier 2: GSAP ScrollTrigger

Use when: Choreographed sequences, pinning, horizontal scroll, split text, staggered children, scrub-linked animations. Technology: GSAP 3 + ScrollTrigger plugin + optionally SplitText, Flip. Advantages: Timeline control, pin support, scrub, responsive via matchMedia.

Decision: If the effect needs timeline choreography, scrub, or pinning, use GSAP.

Tier 3: Three.js / WebGL

Use when: 3D scenes, particle systems, model rendering, camera scroll animation. Technology: three@0.169.0 (vanilla, NOT React Three Fiber). Advantages: Full 3D, GPU-powered, immersive experiences.

Decision: Only when the effect is inherently 3D. Never for 2D scroll effects.

Composition Rules

Stagger Timing

• Base stagger: use design-dna motion.duration.stagger (default 0.12s)
• Max visible staggers: 8-12 elements. Beyond that, use batch reveals.
• Stagger direction: follow reading order (left-to-right, top-to-bottom)

Easing Selection by Context

Duration Relationships

• Fast interactions (hover, click feedback): motion.duration.fast (0.3s)
• Standard reveals: motion.duration.normal (0.6s)
• Dramatic/hero sequences: motion.duration.slow (1.0s)
• Between-element stagger: motion.duration.stagger (0.12s)
• Rule: Longer distances = longer durations. Scale proportionally.

Do / Don't

DO

• Consume ALL timing/easing values from design-dna motion tokens
• Clean up ScrollTrigger instances on component unmount
• Use gsap.matchMedia() for responsive animation differences
• Use will-change sparingly and remove after animation completes
• Animate only transform and opacity when possible (compositor-only)
• Respect prefers-reduced-motion: disable or simplify animations
• Use ScrollTrigger.batch() for many identical reveal animations

DON'T

• Hardcode animation values (durations, easings, distances)
• Mix scrub and toggleActions on the same ScrollTrigger
• Put ScrollTrigger on child tweens inside a timeline (put it on the timeline)
• Animate layout properties (width, height, top, left) -- use transforms
• Use transition: all -- list specific properties
• Forget cleanup: always tl.revert() or ScrollTrigger.kill() on unmount
• Create animations without testing on mobile viewports

Anti-Patterns

ScrollTrigger on Child Tweens (CRITICAL)

// WRONG: ScrollTrigger on individual tweens inside timeline
const tl = gsap.timeline();
tl.to('.a', { y: 0, scrollTrigger: { trigger: '.a' } }); // BUG
tl.to('.b', { y: 0, scrollTrigger: { trigger: '.b' } }); // BUG

// RIGHT: ScrollTrigger on the timeline itself
const tl = gsap.timeline({
  scrollTrigger: { trigger: '.section', start: 'top center' }
});
tl.to('.a', { y: 0 });
tl.to('.b', { y: 0 });

Missing Cleanup

// WRONG: No cleanup
useEffect(() => {
  gsap.to('.element', { scrollTrigger: { ... } });
}, []);

// RIGHT: Context-based cleanup
useEffect(() => {
  const ctx = gsap.context(() => {
    gsap.to('.element', { scrollTrigger: { ... } });
  }, containerRef);
  return () => ctx.revert();
}, []);

Missing Responsive Handling

// WRONG: Same animation at all viewport sizes
gsap.to('.hero', { x: 500 });

// RIGHT: Responsive via matchMedia
gsap.matchMedia().add('(min-width: 768px)', () => {
  gsap.to('.hero', { x: 500 });
});
gsap.matchMedia().add('(max-width: 767px)', () => {
  gsap.to('.hero', { x: 200 });
});

Responsive Animation Principles

1. Always use gsap.matchMedia() for viewport-dependent animations
2. Simplify on mobile: Reduce parallax intensity, disable horizontal scroll sections
3. Touch considerations: No hover-dependent animations on mobile
4. Performance budget: Fewer simultaneous animations on mobile
5. Reduced motion: Check prefers-reduced-motion and provide fallback

Performance Guidelines

• Batch similar animations: ScrollTrigger.batch() for repeated reveals
• Transforms only: Animate transform and opacity for 60fps
• Will-change budget: Apply to max 3-5 elements simultaneously
• Lazy ScrollTrigger: Use ScrollTrigger.create() with lazy refresh for off-screen content
• Pin spacing: Always set pinSpacing: true (default) unless layout requires otherwise