Swing/SnapToTicksDrag のバックアップ(No.10)

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 JSlider.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 + 0.5) + trackLeft;
          offset = 0;
          //System.out.println(snappedPos);
        }
        MouseEvent me = new MouseEvent(
          e.getComponent(), e.getID(), e.getWhen(), e.getModifiers(),
          snappedPos, e.getY(),
          e.getXOnScreen(), e.getYOnScreen(),
          e.getClickCount(), e.isPopupTrigger(), e.getButton());
        e.consume();
        super.mouseDragged(me);
      }
    };
  }
});