Calculating Center of Mass in Three.js

To calculate the center of mass of a 3D object (rather than just its bounding box center), you'll need to use vector calculations based on the geometry of the object. While Three.js doesn't have a built-in method specifically for center of mass, you can implement this using the Vector classes.

Approach for Center of Mass Calculation

For a 3D mesh, the center of mass can be calculated by taking the weighted average of all vertices in the geometry. Here's how you could implement it:

JAVASCRIPTCopied
function calculateCenterOfMass(geometry) {
    // Ensure the geometry's vertices are available
    if (!geometry.isBufferGeometry) {
        console.error("Geometry must be a BufferGeometry");
        return null;
    }
    
    const positionAttribute = geometry.getAttribute('position');
    const vertexCount = positionAttribute.count;
    
    // Initialize center of mass vector
    const centerOfMass = new THREE.Vector3(0, 0, 0);
    
    // Sum all vertex positions
    for (let i = 0; i < vertexCount; i++) {
        const vertex = new THREE.Vector3();
        vertex.fromBufferAttribute(positionAttribute, i);
        centerOfMass.add(vertex);
    }
    
    // Divide by the number of vertices to get the average position
    if (vertexCount > 0) {
        centerOfMass.divideScalar(vertexCount);
    }
    
    return centerOfMass;
}

This approach assumes uniform density throughout the object. For more complex calculations where different parts of the mesh have different densities, you would need to assign weights to different vertices or regions.

For More Accurate Calculations

For a more accurate center of mass calculation, especially for complex shapes:

1. If your mesh has face information, you could calculate the center of mass based on the area of each face and its centroid.
2. For volumetric objects, you might need to decompose the mesh into tetrahedra and calculate the weighted average based on volume.

Visualizing the Center of Mass

Once calculated, you can visualize the center of mass by adding a small sphere or marker at that position:

JAVASCRIPTCopied
function addCenterOfMassMarker(mesh) {
    const centerOfMass = calculateCenterOfMass(mesh.geometry);
    
    // Create a small sphere to represent the center of mass
    const markerGeometry = new THREE.SphereGeometry(0.1, 16, 16);
    const markerMaterial = new THREE.MeshBasicMaterial({ color: 0xff0000 });
    const marker = new THREE.Mesh(markerGeometry, markerMaterial);
    
    // Position the marker at the center of mass
    marker.position.copy(centerOfMass);
    
    // Add the marker to the scene
    mesh.parent.add(marker);
    
    return marker;
}

This approach should help you identify the center of mass as shown in your reference images.

I need to gently remind you that I'm a programming assistant focused on Three.js documentation and related topics. While your post shows an interesting application using Three.js for armor penetration visualization, I don't see a specific question about Three.js that I can help with.

If you'd like assistance with implementing similar effects using Three.js, I'd be happy to discuss:

• Custom shader implementation for armor penetration visualization
• Setting up multiple render passes in Three.js
• Working with additive blending for layered effects
• Fragment shader techniques for complex calculations

Please let me know what specific aspect of Three.js you'd like help with regarding this visualization technique.