This is the function:

```
lookat(vec3 eye, vec3 at, vec3 up)
```

As we all know, the up vector can be`(0.0, 1.0, 0.0)`

. It cannot be parallel to the observation vector `n`

, or there will be somethingw wrong.

My question is how to calculate the up vector so that it passes through the point `eye`

and is perpendicular to the `n`

vector.

`n`

.