Perspective matrix convert

The opencv to opengl intrinsics function look a little confusing. It seems different from original opengl intrinsics definition. For example, why ret[2, 2] = far / (far - near), but not ret[2, 2] = -(near+far) / (far - [near).](http://www.songho.ca/opengl/gl_projectionmatrix.html)

def intrinsics_to_projection(
        intrinsics: torch.Tensor,
        near: float,
        far: float,
    ) -> torch.Tensor:
    """
    OpenCV intrinsics to OpenGL perspective matrix

    Args:
        intrinsics (torch.Tensor): [3, 3] OpenCV intrinsics matrix
        near (float): near plane to clip
        far (float): far plane to clip
    Returns:
        (torch.Tensor): [4, 4] OpenGL perspective matrix
    """
    fx, fy = intrinsics[0, 0], intrinsics[1, 1]
    cx, cy = intrinsics[0, 2], intrinsics[1, 2]
    ret = torch.zeros((4, 4), dtype=intrinsics.dtype, device=intrinsics.device)
    ret[0, 0] = 2 * fx
    ret[1, 1] = 2 * fy
    ret[0, 2] = 2 * cx - 1
    ret[1, 2] = - 2 * cy + 1
    ret[2, 2] = far / (far - near)
    ret[2, 3] = near * far / (near - far)
    ret[3, 2] = 1.
    return ret

Start by locating the intrinsics_to_projection entry point and comparing its OpenCV-to-OpenGL coordinate and depth conventions with the referenced OpenGL projection-matrix definition. Done means the intended convention is established and the implementation or its explanation consistently reflects that behavior.