Using Web Workers for Three.js Geometry Operations in Angular

Using a web worker for heavy geometry operations like merging, tessellating, and modifying is definitely a good approach, especially when these operations take significant time (half a minute in your case). This prevents the main thread from being blocked and keeps your UI responsive.

Challenges with Three.js in Web Workers

The issues you're encountering with imports are common when trying to use Three.js in web workers. Here are the main challenges:

1. Three.js is primarily designed for the main thread where it has access to the DOM and WebGL context
2. Some Three.js components may reference browser-specific APIs not available in workers
3. Angular's build system needs special configuration to properly bundle worker code

Solution Approach

1. Proper Worker Setup in Angular

First, ensure your Angular project is properly set up for web workers:

TYPESCRIPTCopied
// In your angular.json
{
  "projects": {
    "your-project": {
      "architect": {
        "build": {
          "options": {
            "webWorkerTsConfig": "tsconfig.worker.json"
          }
        }
      }
    }
  }
}

Create a tsconfig.worker.json file:

JSONCopied
{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "outDir": "./out-tsc/worker",
    "lib": [
      "es2018",
      "webworker"
    ],
    "types": []
  },
  "include": [
    "src/**/*.worker.ts"
  ]
}

2. Import Only What You Need

For Three.js in workers, import only the specific modules you need:

TYPESCRIPTCopied
/// <reference lib="webworker" />

import { BufferGeometry, BufferAttribute } from 'three/src/core/BufferGeometry';
import { Mesh } from 'three/src/objects/Mesh';
import { mergeBufferGeometries } from 'three/examples/jsm/utils/BufferGeometryUtils.js';
import { TessellateModifier } from 'three/examples/jsm/modifiers/TessellateModifier.js';

addEventListener('message', ({ data }) => {
  // Process the geometries here
  const result = processGeometries(data.geometries);
  postMessage(result);
});

function processGeometries(geometriesData) {
  // Convert serialized geometry data back to Three.js geometries
  const geometries = geometriesData.map(geoData => {
    const geometry = new BufferGeometry();
    // Reconstruct the geometry from serialized data
    // ...
    return geometry;
  });
  
  // Merge geometries
  const mergedGeometry = mergeBufferGeometries(geometries);
  
  // Apply tessellation
  const tessellateModifier = new TessellateModifier(8, 6);
  const tessellatedGeometry = tessellateModifier.modify(mergedGeometry);
  
  // Return serialized result
  return serializeGeometry(tessellatedGeometry);
}

function serializeGeometry(geometry) {
  // Convert geometry to a transferable format
  // ...
}

3. Data Transfer Considerations

You'll need to serialize/deserialize Three.js objects when passing between the main thread and worker:

TYPESCRIPTCopied
// In your component
const worker = new Worker(new URL('./geometry.worker.ts', import.meta.url));

worker.onmessage = ({ data }) => {
  // Convert the serialized data back to a Three.js geometry
  const resultGeometry = deserializeGeometry(data);
  // Use the processed geometry
};

// Prepare geometries for the worker
const serializedGeometries = this.scene.children
  .filter(obj => obj.isMesh)
  .map(mesh => serializeGeometry(mesh.geometry));

worker.postMessage({ geometries: serializedGeometries });

// Helper functions for serialization
function serializeGeometry(geometry) {
  // Extract position, normal, uv attributes as ArrayBuffers
  return {
    positions: geometry.attributes.position.array.buffer,
    normals: geometry.attributes.normal?.array.buffer,
    uvs: geometry.attributes.uv?.array.buffer,
    indices: geometry.index?.array.buffer,
    // Include metadata about the arrays
  };
}

function deserializeGeometry(data) {
  // Reconstruct a BufferGeometry from the serialized data
}

Alternative Approaches

If you continue to face issues with Three.js in web workers, consider these alternatives:

1. Chunked Processing: Split your geometry operations into smaller chunks and process them with small delays to avoid blocking the UI

2. OffscreenCanvas: For newer browsers, you can use OffscreenCanvas to run WebGL operations in a worker

3. Simplified Worker Tasks: Move only the pure computational parts to the worker, keeping Three.js operations on the main thread

Using BufferGeometryUtils

The BufferGeometryUtils module is particularly useful for your task. It provides functions like mergeBufferGeometries which is optimized for combining multiple geometries efficiently.

TYPESCRIPTCopied
import { mergeBufferGeometries } from 'three/examples/jsm/utils/BufferGeometryUtils.js';

// Merge multiple geometries into one
const mergedGeometry = mergeBufferGeometries(geometriesArray);

This approach should help you move your heavy geometry operations off the main thread while maintaining compatibility with Angular and Three.js.