What is the matrix equivalent to Camera.WorldToScreenPoint?

Hello,

I'm trying to perform Worldspace to Screen Space operations on a very large number of points. Unfortunately compute shaders are not an option as WebGL is one of the required target platform.

However in the meantime I'd like to use a threaded solution. Although this is not a WebGL supported feature either, it may well be in the future, even if distant. I will need to be able to use an alternative to Camera.WorldToScreenPoint and Camera.ScreenToWorldPoint as they are not thread-safe.

From what i could gather I'd be able to perform a similar solution by doing:

 Matrix4x4 screen2World = Camera.main.projectionMatrix * Camera.main.cameraToWorldMatrix;
 Matrix4x4 world2Screen = screen2World.inverse;
 
 Vector3 point = new Vector3(123, 456, 789); // World space
 Vector3 screenSpace = world2Screen.MultiplyPoint(point); // <-- I want to get the screen space point
 /* Do something with the screen space point */
 point = screen2World.MultiplyPoint(screenSpace); // Convert back to world space

However I am not getting the same results. Is there something I'm missing here?

Any help is much appreciated.