Last update, 12/23/2012. ControlP5 is a GUI and controller library for processing that can be used in authoring, application, and applet mode. Controllers such as Sliders, Buttons, Toggles, Knobs, Textfields, RadioButtons, Checkboxes amongst others are easily added to a processing sketch. They can be arranged in separate control windows, and can be organized in tabs or groups. → read more. Processing.js.