Gradient translucent track JSlider

• download example.jar
• download src.zip
• repository

Code

UIManager.put("Slider.horizontalThumbIcon", new Icon() {
  @Override public void paintIcon(Component c, Graphics g, int x, int y) {}
  @Override public int getIconWidth()  { return 15; }
  @Override public int getIconHeight() { return 64; }
});
UIManager.put("Slider.trackWidth", 64);
UIManager.put("Slider.majorTickLength", 6);

JSlider slider = makeSlider();
slider.setUI(new MetalSliderUI() {
  int[] pallet = makeGradientPallet();
  @Override public void paintTrack(Graphics g) {
    //Color trackColor = !slider.isEnabled()
    //  ? MetalLookAndFeel.getControlShadow() : slider.getForeground();
    boolean leftToRight = true; //MetalUtils.isLeftToRight(slider);
    Color controlDarkShadow = Color.GRAY;
    Color controlHighlight = new Color(200,255,200);
    Color controlShadow = new Color(0,100,0);

    g.translate( trackRect.x, trackRect.y );

    int trackLeft = 0;
    int trackTop = 0;
    int trackRight = 0;
    int trackBottom = 0;

    // Draw the track
    if(slider.getOrientation() == JSlider.HORIZONTAL) {
      trackBottom = (trackRect.height - 1) - getThumbOverhang();
      trackTop = trackBottom - (getTrackWidth() - 1);
      trackRight = trackRect.width - 1;
    }else{
      if(leftToRight) {
        trackLeft = (trackRect.width - getThumbOverhang()) - getTrackWidth();
        trackRight = (trackRect.width - getThumbOverhang()) - 1;
      }else{
        trackLeft = getThumbOverhang();
        trackRight = getThumbOverhang() + getTrackWidth() - 1;
      }
      trackBottom = trackRect.height - 1;
    }

    if(slider.isEnabled()) {
      g.setColor(controlDarkShadow);
      g.drawRect(trackLeft, trackTop,
                 (trackRight - trackLeft) - 1, (trackBottom - trackTop) - 1);

      g.setColor(controlHighlight);
      g.drawLine(trackLeft + 1, trackBottom, trackRight, trackBottom);
      g.drawLine(trackRight, trackTop + 1, trackRight, trackBottom);

      g.setColor(controlShadow);
      g.drawLine(trackLeft + 1, trackTop + 1, trackRight - 2, trackTop + 1);
      g.drawLine(trackLeft + 1, trackTop + 1, trackLeft + 1, trackBottom - 2);
    } else {
      g.setColor(controlShadow);
      g.drawRect(trackLeft, trackTop,
                 (trackRight - trackLeft) - 1, (trackBottom - trackTop) - 1);
    }

    // Draw the fill
    int middleOfThumb = 0;
    int fillTop = 0;
    int fillLeft = 0;
    int fillBottom = 0;
    int fillRight = 0;

    if(slider.getOrientation() == JSlider.HORIZONTAL) {
      middleOfThumb = thumbRect.x + (thumbRect.width / 2);
      middleOfThumb -= trackRect.x; // To compensate for the g.translate()
      fillTop = !slider.isEnabled() ? trackTop : trackTop + 1;
      fillBottom = !slider.isEnabled() ? trackBottom - 1 : trackBottom - 2;

      if(!drawInverted()) {
        fillLeft = !slider.isEnabled() ? trackLeft : trackLeft + 1;
        fillRight = middleOfThumb;
      }else{
        fillLeft = middleOfThumb;
        fillRight = !slider.isEnabled() ? trackRight - 1 : trackRight - 2;
      }
    }else{
      middleOfThumb = thumbRect.y + (thumbRect.height / 2);
      middleOfThumb -= trackRect.y; // To compensate for the g.translate()
      fillLeft = !slider.isEnabled() ? trackLeft : trackLeft + 1;
      fillRight = !slider.isEnabled() ? trackRight - 1 : trackRight - 2;

      if(!drawInverted()) {
        fillTop = middleOfThumb;
        fillBottom = !slider.isEnabled() ? trackBottom - 1 : trackBottom - 2;
      }else{
        fillTop = !slider.isEnabled() ? trackTop : trackTop + 1;
        fillBottom = middleOfThumb;
      }
    }

    if(slider.isEnabled()) {
      g.setColor(slider.getBackground());
      g.drawLine(fillLeft, fillTop, fillRight, fillTop );
      g.drawLine(fillLeft, fillTop, fillLeft, fillBottom );

      double x = (fillRight - fillLeft) / (double)(trackRight - trackLeft);
      g.setColor(getColorFromPallet(pallet, x));
      g.fillRect(fillLeft+1,fillTop+1,fillRight-fillLeft,fillBottom-fillTop);
    }else{
      g.setColor(controlShadow);
      g.fillRect(fillLeft,fillTop,fillRight-fillLeft,trackBottom-trackTop);
    }

    int yy = trackTop + (trackBottom - trackTop) /2;
    for(int i=10;i>=0;i--) {
      g.setColor( new Color(1f,1f,1f,i*0.07f) );
      g.drawLine( trackLeft+2, yy, (trackRight - trackLeft), yy );
      yy--;
    }
    g.translate(-trackRect.x, -trackRect.y);
  }
});

private static int[] makeGradientPallet() {
  BufferedImage image = new BufferedImage(100, 1, BufferedImage.TYPE_INT_RGB);
  Graphics2D g2  = image.createGraphics();
  Point2D start  = new Point2D.Float(0f, 0f);
  Point2D end  = new Point2D.Float(99f, 0f);
  float[] dist   = {0.0f, 0.5f, 1.0f};
  Color[] colors = { Color.RED, Color.YELLOW, Color.GREEN };
  g2.setPaint(new LinearGradientPaint(start, end, dist, colors));
  g2.fillRect(0, 0, 100, 1);
  int width  = image.getWidth(null);
  int[] pallet = new int[width];
  PixelGrabber pg = new PixelGrabber(image, 0, 0, width, 1, pallet, 0, width);
  try{
    pg.grabPixels();
  }catch(Exception e) {
    e.printStackTrace();
  }
  return pallet;
}
private static Color getColorFromPallet(int[] pallet, float x) {
  int i = (int)(pallet.length * x);
  int max = pallet.length-1;
  int index = i<0?0:i>max?max:i;
  int pix = pallet[index] & 0x00ffffff | (0x64 << 24);
  return new Color(pix, true);
}

References

• Harmonic Code: Varying gradients...
• Gradient translucent track JSlider(Japanese)