JSliderのSnapToTicksをマウスのドラッグでも適用する

slider.setUI(new MetalSliderUI() {
  @Override protected TrackListener createTrackListener(final JSlider slider) {
    return new TrackListener() {
      @Override public void mouseDragged(MouseEvent e) {
        if (!slider.getSnapToTicks() || slider.getMajorTickSpacing() == 0) {
          super.mouseDragged(e);
          return;
        }
        // case SwingConstants.HORIZONTAL:
        int halfThumbWidth = thumbRect.width / 2;
        final int trackLength = trackRect.width;
        final int trackLeft = trackRect.x - halfThumbWidth;
        final int trackRight = trackRect.x + trackRect.width - 1 + halfThumbWidth;
        int xPos = e.getX();
        int snappedPos = xPos;
        if (xPos <= trackLeft) {
          snappedPos = trackLeft;
        } else if (xPos >= trackRight) {
          snappedPos = trackRight;
        } else {
          // int tickSpacing = slider.getMajorTickSpacing();
          // float actualPixelsForOneTick =
          //     trackLength * tickSpacing / (float) slider.getMaximum();

          // a problem if you choose to set a negative MINIMUM for the JSlider;
          // the calculated drag-positions are wrong.
          // Fixed by bobndrew:
          int possibleTickPositions = slider.getMaximum() - slider.getMinimum();
          int tickSpacing = (slider.getMinorTickSpacing() == 0)
              ? slider.getMajorTickSpacing()
              : slider.getMinorTickSpacing();
          float actualPixelsForOneTick =
              trackLength * tickSpacing / (float) possibleTickPositions;
          xPos -= trackLeft;
          snappedPos = (int) (Math.round(
              xPos / actualPixelsForOneTick) * actualPixelsForOneTick + .5) + trackLeft;
          offset = 0;
          // System.out.println(snappedPos);
        }
        e.translatePoint(snappedPos - e.getX(), 0);
        super.mouseDragged(e);
      }
    };
  }
});