Enhancing Objects with a Custom Glow Shader in Three.js

Shaders in Three.js allow for highly customizable visual effects, and one of the most striking effects is the “glow” or “neon” effect. The provided code defines a custom shader material that applies a glowing effect to an object in a Three.js scene. This article explores how the shader works and how it can be used to enhance objects dynamically.

Understanding the Shader Code

The shader is defined using GLSL, comprising a vertex shader and a fragment shader.

Vertex Shader

varying vec2 vUv;
void main() {
  vUv = uv;
  gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
}

• The vUv variable stores the object’s UV coordinates, which are later used in the fragment shader.
• The vertex shader applies the standard transformation using projectionMatrix and modelViewMatrix.

Fragment Shader

uniform vec3 glowColor;
uniform float intensity;
void main() {
  gl_FragColor = vec4(glowColor * intensity, 1.0);
}

• glowColor is a uniform variable that holds the color of the glow.
• intensity scales the brightness of the glow effect.
• The final color output is set to glowColor * intensity with full opacity.

Applying the Glow Effect

The function applyGlow() dynamically replaces the material of an object (or parts of it) with the glow shader.

Function Breakdown

export function applyGlow(object, materialName, intensity = 3.0, color = null)

• object: The Three.js object to which the glow effect should be applied.
• materialName: The name of the material that should be replaced with the glow shader.
• intensity: The strength of the glow effect (default is 3.0).
• color: (Optional) The glow color. If not specified, it derives from the object’s original material.

Creating the Glow Material

const neonMaterial = new THREE.ShaderMaterial({
  uniforms: {
    glowColor: { value: glowColor },
    intensity: { value: intensity }
  },
  vertexShader: shaders.vertex,
  fragmentShader: shaders.fragment,
  side: THREE.DoubleSide,
  transparent: false,
  depthWrite: true
});

• A new ShaderMaterial is created using the custom shaders.
• uniforms allow for dynamic control of the glow color and intensity.
• DoubleSide ensures the effect is applied on both sides of the object.

Replacing the Material in the Object Hierarchy

object.traverse(child => {
  if (child.isMesh && child.material.name === materialName) {
    if (!color) {
      glowColor.copy(child.material.color);
      neonMaterial.uniforms.glowColor.value = glowColor;
    }
    child.material = neonMaterial;
  }
});

• The function traverses all child meshes of the given object.
• If a mesh’s material name matches materialName, its material is replaced with neonMaterial.
• If no color is provided, the original material color is used.

How to Use the Function

Here’s an example of applying the glow effect to a mesh:

import { applyGlow } from './glowShader';

const geometry = new THREE.SphereGeometry(1, 32, 32);
const material = new THREE.MeshStandardMaterial({ color: 'red', name: 'glowingMat' });
const sphere = new THREE.Mesh(geometry, material);
scene.add(sphere);

// Apply the glow effect
applyGlow(sphere, 'glowingMat', 4.0, '#ff00ff');

This will replace the glowingMat material of the sphere with a bright pink glow effect.

Potential Enhancements

• Transparency: Setting transparent: true in ShaderMaterial can allow for blending effects.
• Edge Glow: Modify the fragment shader to make the glow effect more pronounced at the edges.
• Animation: Dynamically adjust intensity in the render loop to create a pulsating glow effect.

Conclusion

This shader-based glow effect provides a lightweight and customizable way to add a neon or emissive appearance to objects in a Three.js scene. By dynamically adjusting the intensity and color, you can create visually stunning highlights for objects in your 3D environment.