The Model Layer: Beyond Simple Data Storage

In traditional MVC, models are often treated as passive data containers. In 3D applications, however, models must handle:

• Spatial relationships - Parent-child hierarchies, collision detection boundaries
• Animation state - Current frame in sequences, morph targets, skinning data
• Physics properties - Mass, velocity, material properties for simulations
• Metadata - Custom properties for business logic (e.g., product SKUs in a catalog)

A well-designed 3D model layer acts as a single source of truth that prevents the common "dual state" problem where Three.js object properties and application data become desynchronized. For example, in an e-commerce 3D configurator, the model might track:

productModel = {
  id: "SKU-45923",
  basePrice: 899.99,
  currentConfiguration: {
    color: { hex: 0x3a5f8e, name: "Midnight Blue" },
    material: "fabric",
    dimensions: { width: 2.1, depth: 0.9, height: 1.1 }
  },
  physics: {
    mass: 18.5,
    centerOfGravity: { x: 0, y: 0.2, z: 0 }
  },
  animationState: {
    current: "idle",
    queue: ["open_drawer", "rotate_90"]
  }
}
                

Crucially, this model would not contain any Three.js-specific objects like Meshes or Materials. Those belong in the view layer, which we'll examine next.

The Controller Layer: Bridging Interaction and Simulation

Controllers in 3D applications must handle more complex input scenarios than traditional web apps:

• 3D spatial input - Raycasting, drag-and-drop in 3D space
• Physics interactions - Collision responses, force applications
• Animation sequencing - Coordinating complex motion paths
• Multi-modal input - VR controllers, touch, mouse, and keyboard simultaneously

A well-architected controller layer in a Three.js application might implement:

class ProductConfiguratorController {
  constructor(model, view) {
    this.model = model;
    this.view = view;

    // Input bindings
    this.setupMouseControls();
    this.setupVRControls();
    this.setupKeyboardShortcuts();

    // Physics bindings
    this.setupCollisionHandlers();

    // Animation queue management
    this.animationScheduler = new AnimationScheduler(model);
  }

  handleColorChange(newColor) {
    this.model.updateConfiguration({ color: newColor });
    this.view.updateMaterials();

    // Trigger associated animations
    if (newColor.name === "Metallic Red") {
      this.animationScheduler.queue("highlight_trim");
    }
  }

  // ... additional methods for other interactions
}
                

The controller's most critical responsibility is maintaining temporal consistency—ensuring that user inputs, physics simulations, and animations all progress through time in a coordinated manner. This becomes particularly challenging in applications with:

• Networked multiplayer interactions
• Physics simulations running at different timesteps than rendering
• Animation systems with variable playback speeds