I have been trying to implement [the same aiming system as in Tank Stars][3], but I got a little stuck. I implemented simple stick aiming, which basically aims towards the stick movement. 

[![enter image description here][2]][2]

In Tank Stars, it is much different compared to the simple aim stick. It remembers the last position and uses it as something like a pivot point.

[![Example][1]][1]



I tried to implement a virtual pivot point as in the image given. The red circle is a virtual pivot. The green circle is the stick center point, and the green arrow is the supposed stick movement. This implementation kind of works, but I don't understand how I should update that pivot point.

Is my approach correct? What is the name of this aiming system? I need a bit of help with the math behind it.




 [1]: https://i.sstatic.net/gHS56.png
 [2]: https://i.sstatic.net/fp1VJ.gif
 [3]: https://www.youtube.com/watch?v=5s8XT99Fwh0