Introduction to Animation in Three.js

Welcome to Chapter 7, where we unlock the magic of animation in Three.js! Up until now, we've been creating static 3D scenes. But what truly brings a 3D experience to life is movement. Animation allows us to add dynamism, engagement, and storytelling to our web-based creations, making them feel alive and interactive.

At its core, animation in Three.js (and most graphics engines) is achieved by repeatedly updating the properties of objects in our scene over time. Think of it like drawing a flipbook: each page is a slightly different frame, and when flipped quickly, it creates the illusion of motion. In Three.js, this 'flipping' happens within our animation loop.

The foundation of animation in Three.js is the requestAnimationFrame function. This is a browser API that tells the browser you want to perform an animation and requests that the browser call a specified function to update an animation before the next repaint. This is crucial because it ensures smooth animations and is optimized for performance, pausing when the tab is inactive.

Within the animate function, we'll typically perform three key actions: update the state of our scene (e.g., change an object's position, rotation, or scale), re-render the scene with the updated state, and then schedule the next frame using requestAnimationFrame again.

The most common properties we'll animate are the position, rotation, and scale of Object3D instances (like meshes). We can change these directly, but for more complex or procedural animations, we'll often use values that change over time. This can be as simple as incrementing a value or as complex as using mathematical functions or easing curves.

Let's visualize the animation loop. It's a continuous cycle of updating and rendering, driven by the browser's repaint signal. This is the heartbeat of our animated 3D world.

graph TD
    A[Browser Calls animate()] --> B{Update Scene State};
    B --> C[Render Scene];
    C --> D[Request Next Frame];
    D --> A;

In the following sections, we'll dive into specific techniques for animating these properties, explore animation libraries for more advanced control, and learn how to create visually compelling motion for your Three.js projects.