Ray intersection and child camera

Question

I've been playing with three.js for few weeks now and got few inconsistencies on ray casting. Here is a simplified version demonstrating one of the bug I encoutered :

http://jsfiddle.net/eMrhb/12/

The camera is added to the sphere mesh for further use of TrackBallControl for example.

scene.add(mesh);    
mesh.add(camera);

Clicking a few times on the sphere and opening the console, show us none of the expected intersections between the ray and the mesh.

Adding the camera to the scene (http://jsfiddle.net/eMrhb/9/), solves the problem:

scene.add(mesh);    
scene.add(camera);

But I could use a much more complex hierarchy between my scene objects and the camera to suit my needs.

Is this a limitation? If it is, is there any workarounds I could use?

I am not sure why you are getting down-voted. This seems like a very good question to me... — WestLangley
Perhaps it is because you are not adding the camera directly to the scene in the second fiddle, as you claim. — WestLangley
Excuse my (english) mistake, directly wasn't the right word, I'll fix that. — lutangar
Thank you anyway @WestLangley, I was seriously questionning the pertinence of the question myself. That's a relief to hear from you! — lutangar

WestLangley WestLangley · Accepted Answer · 2012-12-14T15:12:52

Yes, this is fixable.

If the camera is a child of another object that is rotated and or translated, then your have to use a different pattern in ray casting.

Instead of this familiar pattern:

var ray = new THREE.Ray( camera.position, vector.subSelf( camera.position ).normalize() );

You have to use this pattern instead:

var position = camera.matrixWorld.getPosition().clone();
var ray = new THREE.Ray( position, vector.subSelf( position ).normalize() );

three.js r.53

Ray intersection and child camera

1 Answers