docs: public void setAlphaSliderVisible(boolean visible) {
      if (showAlphaPanel != visible) {
        showAlphaPanel = visible;
  
        /*
         * Force recreation.
         */
        valShader = null;
        satShader = null;
        alphaShader = null;
        hueBackgroundCache = null;
        satValBackgroundCache = null;
  
        requestLayout();
      }
    }