Welcome to Chapter 4, where we'll explore one of the most crucial elements in making your 3D scenes feel alive and believable: lighting and shadows. Without light, your 3D world would be a flat, featureless void. Light is what defines shapes, creates mood, and guides the viewer's eye. In this section, we'll start by understanding the fundamental concepts of lighting in 3D graphics.
Think about how light works in the real world. It emanates from sources like the sun, a lamp, or a candle. This light then bounces off surfaces, illuminating them and casting shadows. In 3D, we simulate these same principles to create visually appealing scenes. Three.js provides a variety of light types that mimic these real-world phenomena.
The primary goal of lighting in 3D is to interact with the materials of your objects. The way light hits a surface depends on its material properties – is it shiny, matte, transparent, or rough? Lighting and materials work hand-in-hand to determine the final appearance of your rendered scene. Without any lights, objects will appear flat and unlit, regardless of their material.
To get started with lighting in Three.js, you'll typically need two main components: a light source and a material that can react to light. Not all materials are affected by lights; for example, a MeshBasicMaterial will render the same regardless of lighting. However, materials like MeshLambertMaterial, MeshPhongMaterial, and MeshStandardMaterial are designed to interact with light, creating more realistic effects.
Here's a basic conceptual flow of how lighting is handled in a 3D scene:
graph TD;
A[Light Source] --> B(Light Rays);
B --> C{Object Surface};
C --> D[Illumination];
C --> E[Shadow Casting];
D --> F[Viewer];
E --> F;
In Three.js, you'll create an instance of a light object (e.g., new THREE.AmbientLight(), new THREE.DirectionalLight()) and add it to your scene. Then, you'll apply a light-reactive material to your 3D objects. As the renderer processes the scene, it calculates how the light interacts with each object's geometry and material, determining the final pixel colors.