Detecting When Objects Are Added to the Visual Scene in Three.js

Based on the available information, Three.js doesn't provide a direct event or method specifically for detecting when an object becomes part of the rendered scene (as opposed to just being added to the object hierarchy).

However, you can implement a solution by combining the existing hierarchy events with scene traversal to determine when an object is actually connected to the scene graph.

Approach

You can create a custom solution by:

1. Listening for the standard added event on your objects
2. When this event fires, traversing upward through the parent chain to check if the root ancestor is a Scene object

Implementation Example

JAVASCRIPTCopied
// Function to check if an object is in the scene
function isInScene(object) {
  let current = object;
  
  // Traverse up the parent chain
  while (current.parent !== null) {
    current = current.parent;
    // Check if we've reached a Scene object
    if (current instanceof THREE.Scene) {
      return true;
    }
  }
  
  return false;
}

// Add this listener to any object you want to track
myObject.addEventListener('added', function(event) {
  // Wait a frame to ensure the hierarchy is fully updated
  requestAnimationFrame(() => {
    if (isInScene(this)) {
      console.log('This object is now part of the rendered scene!');
      // Your custom logic here
    } else {
      console.log('This object was added to a parent, but not yet in the scene');
    }
  });
});

Alternative Approach

You could also implement a polling mechanism that periodically checks if objects have been added to the scene:

JAVASCRIPTCopied
// Store references to objects you want to track
const trackedObjects = [];

// Function to check all tracked objects
function checkObjectsInScene() {
  for (const obj of trackedObjects) {
    // If the object wasn't in scene before but is now
    if (!obj._wasInScene && isInScene(obj)) {
      obj._wasInScene = true;
      console.log('Object added to scene:', obj);
      // Trigger your custom logic
    }
    // If the object was in scene before but isn't now
    else if (obj._wasInScene && !isInScene(obj)) {
      obj._wasInScene = false;
      console.log('Object removed from scene:', obj);
      // Trigger your custom logic
    }
  }
}

// Call this in your animation loop or set up an interval

Note that these approaches are custom implementations since Three.js doesn't provide a built-in mechanism specifically for detecting when objects become part of the rendered scene.