Processing: Scaling Exemplar

So I have been looking through the exemplars to get both inspiration and also code in which I could add to my own animations. One that really caught my eye is the scaling shape exemplar. When the user moves the mouse along the x-axis, the shape enlarges or shrinks accordingly. I felt that this piece of code could really help in my own personal animations and thus I wanted to document it respectively. 

The exemplar has no author to credit, except a credit to George Brower for the Illustration..

This is the code of the exemplar that I found.

However these two lines of code are all that is required for my own animations.