Implementing Dynamic Wall Visibility in Three.js

To implement a feature where walls become hidden when the camera is directed at them from the outside, you can use a combination of raycasting and visibility toggling. Here are some approaches to achieve this effect:

Approach 1: Raycasting with Camera Direction

You can use Three.js's raycasting to determine when the camera is facing a wall:

JAVASCRIPTCopied
// Set up the raycaster
const raycaster = new THREE.Raycaster();
const walls = []; // Array of your wall mesh objects

// In your animation loop
function checkWallVisibility() {
  // Get camera direction
  const cameraDirection = new THREE.Vector3();
  camera.getWorldDirection(cameraDirection);
  
  // Set up the ray from camera position in camera direction
  raycaster.set(camera.position, cameraDirection);
  
  // Check for intersections with walls
  const intersects = raycaster.intersectObjects(walls);
  
  // Hide walls that are being intersected
  walls.forEach(wall => {
    // Reset visibility
    wall.visible = true;
    
    // If this wall is in the intersects array and camera is outside
    intersects.forEach(intersect => {
      if (intersect.object === wall) {
        // Check if camera is outside the wall (using normal direction)
        const normal = intersect.face.normal.clone();
        normal.transformDirection(wall.matrixWorld);
        
        // If dot product is negative, camera is facing the front of the wall
        if (normal.dot(cameraDirection) < 0) {
          wall.visible = false;
        }
      }
    });
  });
}

Approach 2: Using CameraHelper for Visualization

You can use a CameraHelper to better understand the camera's frustum and adjust your logic:

JAVASCRIPTCopied
// Create a camera helper to visualize the camera
const cameraHelper = new THREE.CameraHelper(camera);
scene.add(cameraHelper);

// Only needed during development

Approach 3: Distance-Based Visibility

Another approach is to check the distance between the camera and each wall:

JAVASCRIPTCopied
function updateWallVisibility() {
  walls.forEach(wall => {
    // Get wall center in world coordinates
    const wallPosition = new THREE.Vector3();
    wall.getWorldPosition(wallPosition);
    
    // Calculate distance to camera
    const distanceToCamera = camera.position.distanceTo(wallPosition);
    
    // Get direction from camera to wall
    const directionToWall = wallPosition.clone().sub(camera.position).normalize();
    
    // Get camera's forward direction
    const cameraDirection = new THREE.Vector3();
    camera.getWorldDirection(cameraDirection);
    
    // Calculate dot product to determine if camera is facing the wall
    const dotProduct = cameraDirection.dot(directionToWall);
    
    // If camera is close to wall and facing it, hide the wall
    if (distanceToCamera < 5 && dotProduct > 0.7) {
      wall.visible = false;
    } else {
      wall.visible = true;
    }
  });
}

Implementation Tips

1. Make sure to call your visibility checking function in your animation loop
2. You may need to adjust thresholds based on your scene scale
3. Consider using material opacity instead of toggling visibility for a smoother transition:

JAVASCRIPTCopied
// Instead of toggling visibility, you can fade walls in/out
wall.material.transparent = true;
wall.material.opacity = facingWall ? 0.2 : 1.0;

4. For complex buildings, you might need to implement room-based culling rather than just wall-based

Remember to adjust these examples to fit your specific scene setup and requirements.