scroll-animations

name	scroll-animations
description	Use when triggering animations on scroll - reveal effects, parallax, sticky headers, progress indicators, or any scroll-linked motion.

Scroll Animations

Apply Disney's 12 principles to scroll-triggered motion.

Principle Application

Squash & Stretch: Elements can compress slightly while scrolling fast, settle when stopped.

Anticipation: Content should be slightly visible before full reveal. Start animations at 10-20% visibility.

Staging: Reveal content in reading order. Top-to-bottom, left-to-right progression.

Straight Ahead vs Pose-to-Pose: Define clear "hidden" and "revealed" poses. Scroll position interpolates between them.

Follow Through & Overlapping: Stagger reveals. First element triggers at 20% viewport, next at 25%, etc.

Slow In/Slow Out: Use ease-out for reveals triggered by scroll. Content settles into place.

Arcs: Parallax elements move on curves relative to scroll. Slight horizontal offset as vertical scroll occurs.

Secondary Action: Fade + slide + scale can combine for richer reveals.

Timing:

• Reveal animation: 400-600ms (allows scroll to continue)
• Parallax: real-time, 1:1 or fractional ratios
• Sticky transitions: 200-300ms

Exaggeration: Subtle for scroll - users control the pace. Let scroll speed be the exaggeration.

Solid Drawing: Elements should never jump or teleport. Smooth interpolation at all scroll positions.

Appeal: Scroll animations should reward exploration, not obstruct it.

Timing Recommendations

Scroll Animation	Duration	Trigger Point	Easing
Fade In	500ms	20% visible	ease-out
Slide Up	600ms	15% visible	ease-out
Parallax	real-time	continuous	linear
Sticky Header	200ms	threshold	ease-out
Progress Bar	real-time	continuous	linear
Section Reveal	600ms	25% visible	ease-out

Implementation Patterns

/* Scroll-triggered reveal */
.reveal {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 500ms ease-out, transform 600ms ease-out;
}

.reveal.visible {
  opacity: 1;
  transform: translateY(0);
}

/* CSS-only parallax */
.parallax-container {
  perspective: 1px;
  overflow-y: auto;
}

.parallax-slow {
  transform: translateZ(-1px) scale(2);
}

Intersection Observer Pattern

const observer = new IntersectionObserver(
  (entries) => {
    entries.forEach(entry => {
      if (entry.isIntersecting) {
        entry.target.classList.add('visible');
      }
    });
  },
  { threshold: 0.2, rootMargin: '0px 0px -10% 0px' }
);

document.querySelectorAll('.reveal').forEach(el => observer.observe(el));

Scroll-Linked Animation (CSS)

@keyframes reveal {
  from { opacity: 0; transform: translateY(30px); }
  to { opacity: 1; transform: translateY(0); }
}

.scroll-reveal {
  animation: reveal linear both;
  animation-timeline: view();
  animation-range: entry 0% entry 50%;
}

Key Rules

1. Never block scroll or hijack scroll behavior
2. Animations should complete within viewport, not require precise scroll position
3. Trigger early (10-20% visible) so animation completes before full view
4. Provide prefers-reduced-motion alternative - instant reveals, no parallax
5. Test on mobile - scroll animations must be smooth at 60fps