// use this function to calibrate force coefficients in real time
  public void controllers() {

    cp5 = new ControlP5(this);

    // slider control for gravity
    cp5.addSlider("gravY")
        .setPosition(10, height - 60)
        .setRange(0.0f, 0.2f)
        .setSize(200, 10)
        .setColorCaptionLabel(0)
        .setCaptionLabel("gravity");

    // slider control for drag
    cp5.addSlider("drag")
        .setPosition(10, height - 50)
        .setRange(0.0f, 0.2f)
        .setSize(200, 10)
        .setColorCaptionLabel(0);

    // slider control for attractor strength
    cp5.addSlider("attStrength")
        .setPosition(10, height - 35)
        .setRange(0.0f, 0.2f)
        .setSize(200, 10)
        .setColorCaptionLabel(0);

    // slider control for max wind speed
    cp5.addSlider("maxWind")
        .setPosition(10, height - 10)
        .setRange(0.0f, 0.25f)
        .setSize(200, 10)
        .setColorCaptionLabel(0);

    // background color
    cp =
        cp5.addColorPicker("picker")
            .setPosition(10, 65)
            .setColorValue(color(0xff40B785, 255))
            .hideBar();
  }