Android Giveaway of the Day - Visual FFT

This application allows to see the action of the Fast Fourier Transform (FFT) of the complex plane in the complex plane.
I have always been fascinated by the Mathematical theory of Fourier series, in particular, convergence problems...
But that's too long a story.
The link between physical reality and the need to use the Fourier transformation is little or badly commented on in French education.
This teaching is unfortunately too fragmented!
And to better understand the result of the action of the Fourier transform, I designed this app to visualize on samples of different sizes.
I wish I had this when I was a student!