Create Scroll-Based Animations

Link scroll position to timelines, animations, and 3D objects to create immersive scrollytelling experiences. Works in Unity and Blender.

Drive timelines, animations, and object properties with page scroll position to create engaging narrative experiences.

View Live Demo →

:::tip Works with Unity and Blender The ScrollFollow component is available for both Unity and Blender integrations. :::

What You Can Do

• Timeline Scrubbing - Control Unity Timeline playback with scroll position

• Animator Control - Drive animation state machines based on scroll

• Audio Playback - Sync audio to scroll position for narrated experiences

• Object Movement - Move 3D objects vertically as users scroll

• Spline Following - Control camera paths along splines

• Light Intensity - Fade lights in/out based on scroll

• Custom Properties - Drive any property with scroll values

Perfect for:

• Product storytelling and reveals

• Interactive tutorials and guides

• Narrative-driven experiences

• Portfolio showcases

• Educational content

• Marketing campaigns

Quick Start

Basic Timeline Setup

In Unity or Blender:

1. Create a Timeline with your animations and camera movements

2. Add a PlayableDirector component to control the timeline

3. Add a ScrollFollow component to the same GameObject

4. Assign the PlayableDirector to ScrollFollow's Target property

5. Export and scroll - your timeline now scrubs with the page!

With HTML Markers

For precise control over timeline sections, add markers in your HTML:

<div data-timeline-marker="0.0">Introduction</div>
<div data-timeline-marker="0.5">Product Features</div>
<div data-timeline-marker="1.0">Call to Action</div>

The timeline will smoothly transition between these markers as they scroll into view.

Settings

Setting	What it does
Target	Object(s) to control with scroll (see supported types below)
Damping	Smoothness of scroll response (0 = instant, higher = smoother)
Invert	Reverse scroll direction (scrolling down = value decreases)
HTML Selector	CSS selector for custom scroll container (experimental)
Changed	Event fired when scroll position changes

Supported Target Types

The ScrollFollow component can drive many different component types:

PlayableDirector (Timeline)

Scrubs timeline playback based on scroll position. Use with HTML markers for section-based control.

How it works:

• Scroll position maps to timeline time (0 = start, 1 = end)

• Timeline markers can be linked to HTML elements

• Automatically pauses and evaluates timeline

Animator

Sets a float parameter named "scroll" on the Animator component.

How to use:

1. Create a float parameter named "scroll" in your Animator

2. Create transitions based on this parameter

3. Assign the Animator to ScrollFollow's target

Animation

Controls animation playback time directly.

How it works:

• Scroll position maps to animation time

• 0 = animation start, 1 = animation end

AudioSource

Scrubs audio playback position based on scroll.

Use cases:

• Narrated scrolling experiences

• Sound effects tied to visual reveals

• Music synchronized with scroll

SplineWalker

Moves objects along a spline path as users scroll.

How it works:

• Scroll position sets the position01 property

• Perfect for camera paths and object reveals

Light

Controls light intensity with scroll position.

How it works:

• 0 = light off, 1 = full intensity

• Create fade-in/fade-out effects

Object3D

Moves objects vertically based on scroll position.

How it works:

• Objects move within their bounding box height

• Natural parallax-like movement

Custom Objects

Any object with a scroll property (number or function) can be controlled.

Example:

export class CustomScrollTarget extends Behaviour {
    scroll: number = 0; // Will be set by ScrollFollow

    update() {
        // Use this.scroll (0-1 value) for custom behavior
        this.gameObject.scale.setScalar(this.scroll);
    }
}

Examples

Product Reveal Timeline

Create a scrolling product showcase:

View Live Example →

1. Set up a Timeline with:

   • Camera animations revealing product details

   • Product rotation and zoom

   • UI elements appearing at key moments

2. Add PlayableDirector and ScrollFollow components

3. Add HTML markers for each section:

<div data-timeline-marker="0.0">
  <h2>Introducing the Product</h2>
</div>
<div data-timeline-marker="0.33">
  <h2>Premium Materials</h2>
</div>
<div data-timeline-marker="0.66">
  <h2>Advanced Features</h2>
</div>
<div data-timeline-marker="1.0">
  <h2>Order Now</h2>
</div>

Animator-Based Scroll

Control animation states with scroll:

1. Create an Animator with a float parameter "scroll"

2. Set up animation states and transitions:

   • State 1: "Idle" (scroll < 0.3)

   • State 2: "Opening" (scroll 0.3 - 0.7)

   • State 3: "Opened" (scroll > 0.7)

3. Add ScrollFollow component

4. Assign the Animator to the target

Camera Path with Spline

Create a camera that follows a path as users scroll:

1. Create a spline path for your camera

2. Add SplineWalker component to the camera

3. Add ScrollFollow component

4. Assign the SplineWalker to the target

5. Camera smoothly follows the path based on scroll

Parallax Object Movement

Create depth with scrolling objects:

1. Add ScrollFollow to multiple objects at different depths

2. Assign each object as its own target

3. Adjust Damping differently for each layer

4. Objects move at different speeds creating parallax

Scripting

Listen to Scroll Changes

React to scroll position changes in your code:

import { Behaviour, ScrollFollow, serializable } from "@needle-tools/engine";

export class ScrollListener extends Behaviour {

    @serializable(ScrollFollow)
    scrollFollow?: ScrollFollow;

    start() {
        this.scrollFollow?.changed.addEventListener((evt) => {
            console.log("Scroll value:", evt.value);

            // Prevent default scroll handling if needed
            if (evt.value > 0.5) {
                evt.preventDefault();
            }
        });
    }
}

Get Current Scroll Value

Access the current scroll position:

import { Behaviour, ScrollFollow, serializable } from "@needle-tools/engine";

export class ScrollReader extends Behaviour {

    @serializable(ScrollFollow)
    scrollFollow?: ScrollFollow;

    update() {
        if (this.scrollFollow) {
            const value = this.scrollFollow.currentValue;
            // value is 0-1, where 0 = top, 1 = bottom

            if (value > 0.8) {
                console.log("Near bottom of page!");
            }
        }
    }
}

Custom Scroll Target

Create components that respond to scroll:

import { Behaviour } from "@needle-tools/engine";

export class FadeOnScroll extends Behaviour {

    // ScrollFollow will set this property
    scroll(value: number) {
        // Fade object based on scroll position
        const material = this.gameObject.getComponent(Renderer)?.sharedMaterial;
        if (material) {
            material.opacity = value;
            material.transparent = true;
        }
    }
}

Multiple Targets

Drive multiple components with one ScrollFollow:

import { Behaviour, ScrollFollow, PlayableDirector, Light } from "@needle-tools/engine";

export class ScrollSetup extends Behaviour {

    start() {
        const scrollFollow = this.gameObject.addComponent(ScrollFollow);

        // Control multiple targets at once
        scrollFollow.target = [
            this.gameObject.getComponent(PlayableDirector)!,
            this.gameObject.findByName("MainLight")!.getComponent(Light)!,
        ];

        scrollFollow.damping = 0.3; // Smooth scrolling
    }
}

Timeline Markers

Timeline markers provide precise control over scroll-based storytelling:

Unity Timeline Markers

In Unity, add custom markers to your Timeline:

1. Create a Timeline asset

2. Add markers at key moments

3. Name them descriptively

4. ScrollFollow automatically links them to HTML elements by index

HTML Markers

Define scroll points in your HTML with data-timeline-marker:

<!-- Normalized time values (0.0 to 1.0) -->
<section data-timeline-marker="0.0">
  <h1>Start</h1>
  <p>Beginning of the experience</p>
</section>

<section data-timeline-marker="0.25">
  <h2>First Feature</h2>
  <p>Description appears here</p>
</section>

<section data-timeline-marker="0.5">
  <h2>Second Feature</h2>
  <p>More content</p>
</section>

<section data-timeline-marker="1.0">
  <h2>Conclusion</h2>
  <p>End of timeline</p>
</section>

How Markers Work

• Each marker corresponds to a time in your timeline

• When a marker's HTML element is in view, the timeline scrubs to that time

• Smooth blending occurs between visible markers

• Timeline stays at a marker until the next one comes into view

Advanced Features

Scroll Damping

Control how smoothly the scroll responds:

• Damping = 0: Instant response (timeline/animation jumps to scroll position)

• Damping = 0.1-0.3: Responsive with slight smoothing

• Damping = 0.5-1.0: Very smooth, floaty response

• Higher values: Increasingly laggy, cinematic feel

Perfect for:

• Low damping: Precise control, interactive experiences

• High damping: Cinematic reveals, smooth storytelling

Inverted Scroll

Set Invert to true to reverse scroll behavior:

• Scrolling down decreases the value (1 → 0)

• Scrolling up increases the value (0 → 1)

Use cases:

• Objects that should descend as you scroll down

• Reverse-narrative experiences

• Custom scroll behaviors

Custom Scroll Container

Use HTML Selector to scroll within a specific element instead of the whole page:

scrollFollow.htmlSelector = "#my-scroll-container";

<div id="my-scroll-container" style="height: 100vh; overflow-y: auto;">
  <!-- Your scrollable content -->
</div>

:::warning Experimental Feature Custom scroll containers are experimental and may change in future updates. :::

Responsive Design Tips

Page Structure

For best results, structure your HTML for clear sections:

<div class="scroll-container">
  <section data-timeline-marker="0.0" class="full-height">
    <h1>Section 1</h1>
  </section>

  <section data-timeline-marker="0.5" class="full-height">
    <h1>Section 2</h1>
  </section>

  <section data-timeline-marker="1.0" class="full-height">
    <h1>Section 3</h1>
  </section>
</div>

.full-height {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
}

Mobile Considerations

• Test scroll behavior on mobile devices

• Adjust damping for touch scrolling (often needs lower values)

• Ensure timeline markers are clearly visible

• Consider longer sections on mobile for easier viewing

Performance

• Use timeline scrubbing instead of real-time animation for better performance

• Limit the number of active ScrollFollow components

• Consider disabling ScrollFollow on low-performance devices

• Use ?debugscroll URL parameter to monitor performance

Common Questions

How do I make the timeline stay at a specific point longer? Add multiple HTML markers with the same timeline time value, or make the HTML section taller.

Can I control multiple timelines with one ScrollFollow? Yes! Add multiple PlayableDirector components to the target array.

Why isn't my timeline moving smoothly? Check that your Timeline has enough keyframes, and consider increasing the damping value.

How do I sync HTML content with timeline events? Use timeline markers that correspond to data-timeline-marker elements. When those elements are in view, the timeline will be at that point.

Can I use this with page scrolling libraries? Yes, ScrollFollow works with most scrolling libraries. For custom scroll containers, use the htmlSelector property.

Does it work on mobile? Yes! ScrollFollow supports touch scrolling on mobile devices.

How do I debug scroll issues? Add ?debugscroll to your URL to see detailed logging:

http://localhost:3000?debugscroll

Debugging

Enable debug mode by adding ?debugscroll to your URL:

http://localhost:3000?debugscroll

This shows:

• Current scroll value and percentage

• Number of active targets

• Timeline marker information and weights

• Scroll position calculations

More Information

Live Examples:

• Product Scrollytelling - Interactive product reveal

• Bike Scrollytelling Demo - Product showcase

• Scrollytelling Template - Starter template

• Bike Demo Repository - Complete source code

API Documentation:

• ScrollFollow API - Complete technical reference

Related Components:

• PlayableDirector - Timeline control

• Animator - Animation state machines

• SplineWalker - Spline path following