"""pytorch3d.renderer.camera_utils stub."""
import torch

def camera_to_eye_at_up(camera):
    """Extract eye, at, up from camera. Minimal stub."""
    R = camera.R if hasattr(camera, "R") else torch.eye(3).unsqueeze(0)
    T = camera.T if hasattr(camera, "T") else torch.zeros(1, 3)
    eye = -torch.bmm(R, T.unsqueeze(-1)).squeeze(-1)
    at = torch.zeros_like(eye)
    up = torch.tensor([[0.0, 1.0, 0.0]])
    return eye, at, up