How to do 3D to camera ray, and get the pixel

[Nickak2003]

I know the camera has a method to get the 3D point from the pixel, but how do I do the reverse?

[spacegaier]

What exactly are you trying to achieve? It's not very clear to me.

[Nickak2003]

I want to take a point in the 3d space, and I assume create a ray, and end up getting a pixel coordinate. So for instance i can make a chat bubble or menu or something.

[Daixiwen]

In that case you don't need a ray, you just need to project your 3D point to 2D. You can for example do that by applying the projection matrix to the coordinates. You'll also probably need to offset the result and multiply by the viewport size to get coordinates.