Welcome to Chapter 8, where we'll dive into the exciting world of shaders and post-processing. These are the advanced tools that truly bring your 3D web experiences to life, allowing for stunning visual effects and unique artistic styles. Before we explore how to implement them in Three.js, it's crucial to understand what shaders are at their core. Think of them as tiny, highly specialized programs that run directly on your graphics card (GPU). They are responsible for determining exactly how each pixel on your screen is rendered, from its color and brightness to its texture and any special effects applied.
At a high level, there are two main types of shaders we'll encounter: the Vertex Shader and the Fragment Shader. Each plays a distinct but complementary role in the rendering pipeline. The Vertex Shader operates on individual vertices (the points that define your 3D models), while the Fragment Shader operates on individual pixels (or more accurately, 'fragments') that make up the final image.
graph TD
A[3D Model Data (Vertices, Normals, UVs)] --> B(Vertex Shader)
B --> C[Transformed Vertices]
C --> D(Rasterization)
D --> E[Fragments (Pixels)]
E --> F(Fragment Shader)
F --> G[Final Pixel Color]
G --> H(Output to Screen)
The Vertex Shader's primary job is to transform the 3D coordinates of your model's vertices from their original model space into the 2D space of your screen. It takes attributes like vertex positions, normals (which describe surface orientation), and texture coordinates as input. It then manipulates these values, often applying transformations like translation, rotation, and scaling, and projecting them onto the camera's view. The output of the Vertex Shader is a set of transformed vertex positions that the GPU can then use to determine which pixels need to be drawn.
attribute vec3 position;
attribute vec3 normal;
varying vec3 vNormal;
uniform mat4 modelViewMatrix;
uniform mat4 projectionMatrix;
void main() {
vNormal = normal;
gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
}The Fragment Shader, also sometimes called the Pixel Shader, is where the magic of color happens. After the Vertex Shader has positioned the vertices and the GPU has figured out which pixels need to be filled in (a process called rasterization), the Fragment Shader is invoked for each individual pixel. Its job is to determine the final color of that pixel. It can read texture data, perform complex lighting calculations, apply fog, and implement all sorts of visual effects. The inputs to the Fragment Shader are interpolated values from the Vertex Shader (like the vNormal in our example) and uniforms (global variables that are the same for all vertices and fragments, like matrices and light colors).