How to get the "anti-clockwise" angle between two 2D vectors?
<p>I have two vectors and I want to get the angle between those vectors, I am currently doing it with this formula :</p>

<pre><code>acos(dot(v1.unitVector, v2.unitVector))
</code></pre>

<p>Here is what I get with it :
<a href="https://i.stack.imgur.com/K5fla.png" rel="nofollow"><img src="https://i.stack.imgur.com/K5fla.png" alt="enter image description here"></a>  </p>

<p>I would want the green angle rather than the red angle, but I don't know what formula I should use...</p>

<p>Thank you.</p>

<p>EDIT : So, hen the vectors are still in a certain position (like the first two pairs of vectors, it's ok, but whenever it is in a configuration like in the third pair, it doesn't give me the right angle anymore)</p>