message: Adjust drag positioning to track center of thumb and match scale
diff: @@ -205,8 +205,8 @@ void Slider::onMouseMove(int x, int y, int /*dX*/, int /*dY*/)
  {
  value(
  (mSliderType == SliderType::Vertical) ?
  - mMax * (y - mSlideBar.y) / mSlideBar.height :
  - mMax * (x - mSlideBar.x) / mSlideBar.width
  + mMax * (y - mSlideBar.y - mSlider.height / 2) / (mSlideBar.height - mSlider.height) :
  + mMax * (x - mSlideBar.x - mSlider.width / 2) / (mSlideBar.width - mSlider.width)
  );
  }
  }
  