SOLVED – Custom threejs Mesh class with InstancedBufferGeometry not being rendered

The Frustrating Problem of the Unseen Mesh

Have you ever spent hours crafting a custom Three.js Mesh class, only to find that it refuses to render on your scene? You’ve triple-checked the code, ensured that the geometry and material are correct, and even resorted to sacrificing a pixel to the coding gods, but still, nothing appears. Well, fear not, dear developer, for you are not alone. In this article, we’ll delve into the common pitfalls and solutions surrounding the use of InstancedBufferGeometry in custom Three.js Mesh classes.

What is InstancedBufferGeometry?

Before we dive into the meat of the issue, let’s take a brief moment to discuss what InstancedBufferGeometry is and why it’s so powerful. InstancedBufferGeometry is a type of geometry in Three.js that allows you to render multiple instances of the same geometry, but with different transformations, using a single draw call. This approach can significantly improve performance, especially when dealing with large numbers of identical objects.

The Culprits Behind the Invisible Mesh

So, what could be causing your custom Mesh class to remain invisible? Let’s explore some common culprits:

• Incorrect Geometry Construction: One of the most common mistakes is constructing the InstancedBufferGeometry incorrectly. This can lead to the geometry being empty or corrupted, resulting in nothing being rendered.
• Insufficient Data in the BufferGeometry: When using InstancedBufferGeometry, you need to ensure that you’re providing enough data for each instance. This includes position, rotation, and scale information.
• Material Issues: A faulty material can cause your Mesh to remain invisible. This might be due to incorrect configuration, missing uniforms, or invalid shader code.
• Scene and Camera Setup: If your scene or camera is not set up correctly, your Mesh might be rendered outside of the camera’s view frustum or hidden behind other objects.

Solution 1: Verify Your Geometry Construction

Let’s start by ensuring that your InstancedBufferGeometry is constructed correctly. Here’s an example of how you might create a custom Mesh class:

class CustomMesh extends THREE.Mesh {
  constructor(geometry, material) {
    super(geometry, material);

    this.geometry = geometry;
    this.material = material;

    this.geometry.setIndex(new THREE.BufferAttribute(new Uint16Array([]), 1));
    this.geometry.setAttribute('position', new THREE.BufferAttribute(new Float32Array([]), 3));
    this.geometry.setAttribute('instancePosition', new THREE.InstancedBufferAttribute(new Float32Array([]), 3, 1));
    // ...
  }
}

Notice how we’re setting the index, position, and instancePosition attributes correctly. Ensure that your geometry is properly initialized and that you’re providing enough data for each attribute.

Solution 2: Provide Sufficient Data for Each Instance

When using InstancedBufferGeometry, you need to provide data for each instance. This includes position, rotation, and scale information. Here’s an example of how you might prepare your instance data:

const instanceData = [];

for (let i = 0; i < numInstances; i++) {
  const position = new THREE.Vector3(Math.random() * 10 - 5, Math.random() * 10 - 5, Math.random() * 10 - 5);
  const rotation = new THREE.Euler(Math.random() * Math.PI, Math.random() * Math.PI, Math.random() * Math.PI);
  const scale = new THREE.Vector3(Math.random() * 2 + 1, Math.random() * 2 + 1, Math.random() * 2 + 1);

  instanceData.push(position.x, position.y, position.z, rotation.x, rotation.y, rotation.z, scale.x, scale.y, scale.z);
}

this.geometry.setAttribute('instancePosition', new THREE.InstancedBufferAttribute(new Float32Array(instanceData), 3, 1));
this.geometry.setAttribute('instanceRotation', new THREE.InstancedBufferAttribute(new Float32Array(instanceData), 3, 1));
this.geometry.setAttribute('instanceScale', new THREE.InstancedBufferAttribute(new Float32Array(instanceData), 3, 1));

In this example, we're generating random instance data for position, rotation, and scale. You should adapt this to fit your specific use case.

Solution 3: Ensure Your Material is Correctly Configured

A faulty material can cause your Mesh to remain invisible. Here are some things to check:

• Vertex and Fragment Shaders: Ensure that your vertex and fragment shaders are correct and functioning as expected.
• Material Properties: Verify that your material properties, such as opacity, transparent, and depthTest, are correctly set.
• Uniforms: Ensure that you're providing all necessary uniforms to your material. This includes instance-specific data, such as position, rotation, and scale.

Here's an example of how you might configure a simple material:

const material = new THREE.ShaderMaterial({
  uniforms: {
    instancePosition: { value: new THREE.InstancedBufferAttribute(new Float32Array(instanceData), 3, 1) },
    instanceRotation: { value: new THREE.InstancedBufferAttribute(new Float32Array(instanceData), 3, 1) },
    instanceScale: { value: new THREE.InstancedBufferAttribute(new Float32Array(instanceData), 3, 1) },
  },
  vertexShader: `
    uniform mat4 modelViewMatrix;
    uniform mat4 projectionMatrix;
    attribute vec3 position;
    attribute vec3 instancePosition;
    attribute vec3 instanceRotation;
    attribute vec3 instanceScale;

    void main() {
      vec3 transformedPosition = position + instancePosition;
      gl_Position = projectionMatrix * modelViewMatrix * vec4(transformedPosition, 1.0);
    }
  `,
  fragmentShader: `
    void main() {
      gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
    }
`);

In this example, we're creating a simple ShaderMaterial with uniforms for instance position, rotation, and scale. We're then using these uniforms in our vertex shader to transform the instance positions.

Solution 4: Verify Your Scene and Camera Setup

Finally, ensure that your scene and camera are set up correctly. This includes:

• Camera Position and Orientation: Verify that your camera is positioned and oriented correctly to view the Mesh.
• Scene Hierarchy: Ensure that your Mesh is added to the correct parent object in the scene hierarchy.
• Object Visibility: Verify that your Mesh is not hidden or disabled.

Here's an example of how you might set up a simple scene and camera:

const scene = new THREE.Scene();
const camera = new THREE.PerspectiveCamera(75, window.innerWidth / window.innerHeight, 0.1, 1000);
const renderer = new THREE.WebGLRenderer({
  canvas: document.getElementById('canvas'),
  antialias: true
});

camera.position.z = 5;

const mesh = new CustomMesh(geometry, material);
scene.add(mesh);

function animate() {
  requestAnimationFrame(animate);
  renderer.render(scene, camera);
}
animate();

In this example, we're creating a simple scene, camera, and renderer. We're then adding our custom Mesh to the scene and rendering it using the animate function.

Conclusion

In this article, we've explored the common pitfalls and solutions surrounding the use of InstancedBufferGeometry in custom Three.js Mesh classes. By verifying your geometry construction, providing sufficient data for each instance, ensuring your material is correctly configured, and verifying your scene and camera setup, you should be able to successfully render your custom Mesh.

If you're still experiencing issues, don't hesitate to reach out to the Three.js community or seek additional resources. Happy coding!

Common Issues	Solutions
Incorrect Geometry Construction	Verify geometry construction, ensure sufficient data for each attribute
Insufficient Data for Each Instance	Provide instance-specific data, such as position, rotation, and scale
Material Issues	Verify material configuration, ensure correct vertex and fragment shaders, and provide necessary uniforms
Scene and Camera Setup Issues	Verify camera position and orientation, ensure correct scene hierarchy, and object visibility

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