How can I set a custom knob (from a png strip) in the way of accept negative values

Hi, I have a MainKnob class that represents a rotary knob (from png strip) and I need to modify it for take the knob accept negative values.

#include "Images.h"

class MainKnob : public LookAndFeel_V3

void drawRotarySlider (Graphics& g, int x, int y, int width, int height, float sliderPos,
                       const float rotaryStartAngle, const float rotaryEndAngle, Slider& slider) override
    Image knob = ImageCache::getFromMemory(Images::mainKnob_png, Images::mainKnob_pngSize);
    int frameCount = knob.getHeight() / knob.getWidth();
    int frameSize = knob.getWidth();
    const double div = slider.getMaximum() / frameCount;
    double pos = (int)(slider.getValue() / div);
    if (pos > 0)
        pos = pos - 1;
    g.drawImage (knob, x, y, width, height, 0, (int)(pos*frameSize), frameSize, frameSize, false);


This is the class. In this way I have a knob that hides if I set negative values…
How do I have to change the class properties?