Standing wave via reflection

The black dots represent a string. Click "Reset", then click the "Play" button to send a traveling wave down the string! Upon reaching the end of the string (at right), the red wave will produce a reflected blue wave. The string will respond to the superposition (sum) of the two traveling waves. The green slider controls whether the end of the string is free or fixed.
This is my attempt at a GeoGebra version of the original Java applet by Walter Fendt, now superseded by his HTML5 interactive animation at