I've made a pure PHP script that uses GD library to put text on an image, text entered from a HTML form. The problem is that i can't give the user the possibility to position the text properly.

I http://lolkot.ru/lolmixer/#1369, kullanıcıların fare ile çok kolay metin ile oynamanıza izin veriyor bu iyi bir örnek buldum!

How is this possible ? What technologies are used for this ?