ControlP5 2dslider limitations

Hi Everyone,

I'm trying to build a custom 2d slider where the sum of the x and y coordinates are less than 20. How can I program this? Here is my current setup for the 2d slider.

cp5 = new ControlP5(this); s = cp5.addSlider2D("wave") .setPosition(30,40) .setSize(100,100) .setMinMax(1,20,20,1) .setValue(1,1) ;

Thank you so much, Jerry