GSAP ScrollTrigger

Scroll-driven animations and interactions.

Quick Start

npm install gsap

import gsap from 'gsap';
import { ScrollTrigger } from 'gsap/ScrollTrigger';

gsap.registerPlugin(ScrollTrigger);

gsap.to('.box', {
  x: 500,
  scrollTrigger: {
    trigger: '.box',
    start: 'top center',
    end: 'bottom center',
    scrub: true
  }
});

Core Concepts

Basic ScrollTrigger

gsap.to('.element', {
  x: 200,
  scrollTrigger: {
    trigger: '.element',  // Element that triggers the animation
    start: 'top center',  // When trigger hits viewport center
    end: 'bottom center', // When trigger leaves viewport center
    toggleActions: 'play pause resume reset'
  }
});

Start/End Positions

// Format: "trigger-position viewport-position"
start: 'top center'      // Trigger's top hits viewport center
start: 'top 80%'         // Trigger's top hits 80% down viewport
start: 'center center'   // Trigger's center hits viewport center
start: 'bottom top'      // Trigger's bottom hits viewport top
start: 'top top+=100'    // Trigger's top hits 100px below viewport top

Position Reference

Value	Description
top	Top edge
center	Center
bottom	Bottom edge
80%	80% from top
+=100	Plus 100 pixels
-=50	Minus 50 pixels

Scrub Animations

Basic Scrub

// Animation progress tied to scroll position
gsap.to('.progress-bar', {
  scaleX: 1,
  scrollTrigger: {
    trigger: '.content',
    start: 'top top',
    end: 'bottom bottom',
    scrub: true  // Directly linked to scroll
  }
});

Smooth Scrub

gsap.to('.element', {
  x: 500,
  scrollTrigger: {
    trigger: '.section',
    scrub: 1,    // 1 second smoothing
    // scrub: 0.5  // 0.5 second smoothing
    // scrub: 2    // 2 second smoothing (laggy feel)
  }
});

Scrub with Timeline

const tl = gsap.timeline({
  scrollTrigger: {
    trigger: '.container',
    start: 'top top',
    end: '+=3000',  // Scroll distance
    scrub: 1,
    pin: true
  }
});

tl.to('.step1', { opacity: 1 })
  .to('.step2', { opacity: 1 })
  .to('.step3', { opacity: 1 });

Pinning

Basic Pin

ScrollTrigger.create({
  trigger: '.panel',
  start: 'top top',
  end: '+=500',      // Pin for 500px of scroll
  pin: true
});

Pin with Animation

gsap.to('.content', {
  x: '-200%',
  ease: 'none',
  scrollTrigger: {
    trigger: '.horizontal-section',
    start: 'top top',
    end: () => '+=' + document.querySelector('.horizontal-section').offsetWidth,
    pin: true,
    scrub: 1
  }
});

Pin Spacing

ScrollTrigger.create({
  trigger: '.section',
  pin: true,
  pinSpacing: true,   // Default: adds space for pinned duration
  // pinSpacing: false  // No extra space (content overlaps)
  // pinSpacing: '500px' // Custom spacing
});

Toggle Actions

Action Syntax

// Format: "onEnter onLeave onEnterBack onLeaveBack"
toggleActions: 'play pause resume reset'

// Common combinations:
toggleActions: 'play none none none'     // Play once
toggleActions: 'play reverse play reverse' // Toggle direction
toggleActions: 'restart none none none'  // Restart each time
toggleActions: 'play complete reverse reset'

Action Values

Action	Effect
play	Play forward
pause	Pause
resume	Resume from paused
reverse	Play backward
restart	Restart from beginning
reset	Reset to start (no animation)
complete	Jump to end
none	Do nothing

Snap Points

Basic Snap

ScrollTrigger.create({
  trigger: '.sections',
  start: 'top top',
  end: 'bottom bottom',
  snap: 1 / 4  // Snap to quarters
});

Snap to Labels

const tl = gsap.timeline({
  scrollTrigger: {
    trigger: '.container',
    scrub: 1,
    snap: {
      snapTo: 'labels',
      duration: 0.5,
      ease: 'power2.inOut'
    }
  }
});

tl.addLabel('intro')
  .to('.a', { opacity: 1 })
  .addLabel('middle')
  .to('.b', { opacity: 1 })
  .addLabel('end');

Snap Configuration

snap: {
  snapTo: [0, 0.25, 0.5, 0.75, 1],  // Snap to specific points
  duration: { min: 0.2, max: 0.6 }, // Snap duration range
  delay: 0,                          // Delay before snap
  ease: 'power1.inOut',             // Snap easing
  directional: true                  // Snap in scroll direction
}

Callbacks

ScrollTrigger Callbacks

ScrollTrigger.create({
  trigger: '.section',
  onEnter: () => console.log('Entered'),
  onLeave: () => console.log('Left'),
  onEnterBack: () => console.log('Entered from bottom'),
  onLeaveBack: () => console.log('Left going up'),
  onUpdate: (self) => console.log('Progress:', self.progress),
  onToggle: (self) => console.log('Active:', self.isActive),
  onRefresh: () => console.log('Refreshed')
});

Progress-Based Updates

ScrollTrigger.create({
  trigger: '.section',
  start: 'top bottom',
  end: 'bottom top',
  onUpdate: (self) => {
    // self.progress: 0 to 1
    // self.direction: 1 (down) or -1 (up)
    // self.velocity: scroll speed
    updateElement(self.progress);
  }
});

Parallax Effects

Basic Parallax

// Background moves slower than scroll
gsap.to('.background', {
  yPercent: -50,
  ease: 'none',
  scrollTrigger: {
    trigger: '.section',
    scrub: true
  }
});

// Foreground moves faster
gsap.to('.foreground', {
  yPercent: 50,
  ease: 'none',
  scrollTrigger: {
    trigger: '.section',
    scrub: true
  }
});

Multi-Layer Parallax

const layers = [
  { selector: '.layer-1', speed: -20 },
  { selector: '.layer-2', speed: -40 },
  { selector: '.layer-3', speed: -60 },
  { selector: '.layer-4', speed: -80 }
];

layers.forEach(layer => {
  gsap.to(layer.selector, {
    yPercent: layer.speed,
    ease: 'none',
    scrollTrigger: {
      trigger: '.parallax-section',
      start: 'top bottom',
      end: 'bottom top',
      scrub: true
    }
  });
});

Horizontal Scrolling

Horizontal Section

const sections = gsap.utils.toArray('.panel');

gsap.to(sections, {
  xPercent: -100 * (sections.length - 1),
  ease: 'none',
  scrollTrigger: {
    trigger: '.horizontal-container',
    pin: true,
    scrub: 1,
    snap: 1 / (sections.length - 1),
    end: () => '+=' + document.querySelector('.horizontal-container').offsetWidth
  }
});

Markers (Development)

ScrollTrigger.create({
  trigger: '.section',
  start: 'top center',
  end: 'bottom center',
  markers: true,  // Show visual markers
  // markers: { startColor: 'green', endColor: 'red', fontSize: '12px' }
});

Batch Animations

Stagger on Scroll

ScrollTrigger.batch('.card', {
  onEnter: (elements) => {
    gsap.from(elements, {
      opacity: 0,
      y: 50,
      stagger: 0.1,
      duration: 0.5
    });
  },
  start: 'top 85%'
});

Batch Configuration

ScrollTrigger.batch('.item', {
  interval: 0.1,  // Time between batches
  batchMax: 3,    // Max items per batch
  onEnter: batch => gsap.to(batch, { opacity: 1, y: 0, stagger: 0.1 }),
  onLeave: batch => gsap.to(batch, { opacity: 0, y: 20 }),
  onEnterBack: batch => gsap.to(batch, { opacity: 1, y: 0 }),
  onLeaveBack: batch => gsap.to(batch, { opacity: 0, y: -20 })
});

Common Patterns

Reveal on Scroll

gsap.utils.toArray('.reveal').forEach(elem => {
  gsap.from(elem, {
    opacity: 0,
    y: 50,
    duration: 0.8,
    scrollTrigger: {
      trigger: elem,
      start: 'top 80%',
      toggleActions: 'play none none none'
    }
  });
});

Progress Indicator

gsap.to('.progress-bar', {
  scaleX: 1,
  transformOrigin: 'left center',
  ease: 'none',
  scrollTrigger: {
    trigger: 'body',
    start: 'top top',
    end: 'bottom bottom',
    scrub: 0.3
  }
});

Sticky Header Transform

ScrollTrigger.create({
  start: 'top -80',
  onUpdate: (self) => {
    if (self.direction === 1) {
      gsap.to('.header', { y: -80, duration: 0.3 });
    } else {
      gsap.to('.header', { y: 0, duration: 0.3 });
    }
  }
});

Temporal Collapse Patterns

Countdown Scroll Reveal

// Reveal countdown sections as user scrolls
const sections = ['days', 'hours', 'minutes', 'seconds'];

sections.forEach((section, i) => {
  gsap.from(`.countdown-${section}`, {
    opacity: 0,
    scale: 0.8,
    y: 50,
    duration: 0.8,
    ease: 'power3.out',
    scrollTrigger: {
      trigger: `.countdown-${section}`,
      start: 'top 80%',
      toggleActions: 'play none none none'
    }
  });
});

Scroll-Based Time Dilation Effect

gsap.timeline({
  scrollTrigger: {
    trigger: '.time-section',
    start: 'top center',
    end: 'bottom center',
    scrub: 1
  }
})
.to('.time-digit', {
  textShadow: '0 0 50px #00F5FF, 0 0 100px #00F5FF',
  scale: 1.1
})
.to('.particles', {
  opacity: 1,
  filter: 'blur(0px)'
}, '<');

Performance Tips

// Disable on mobile if needed
ScrollTrigger.matchMedia({
  '(min-width: 768px)': function() {
    // Desktop animations
  },
  '(max-width: 767px)': function() {
    // Simpler mobile animations
  }
});

// Refresh on resize
ScrollTrigger.refresh();

// Kill all ScrollTriggers
ScrollTrigger.killAll();

// Kill specific trigger
const st = ScrollTrigger.create({ ... });
st.kill();

Reference

• See gsap-fundamentals for animation basics
• See gsap-sequencing for timeline composition
• See gsap-react for React integration with ScrollTrigger