Using GLM's UnProject
<p>I'm not sure how to use the Unproject method provided by GLM.</p>

<p><a href="http://glm.g-truc.net/api/a00147.html#ga540d5f6bb3f41e5dfa38d6ebd8771765" rel="nofollow">http://glm.g-truc.net/api/a00147.html#ga540d5f6bb3f41e5dfa38d6ebd8771765</a></p>

<p>Specifically, in what format is the viewport passed in? And why doesn't the function require a view matrix as well as a projection and world matrix?</p>
