Creating custom JButton from images containing transparent pixels

Question

Read edit 2 for what I'm actually missing to make it work

I'm currently trying to create some custom JButtons using images created in photoshop that have an alpha parameter.

So far, overriding the paint() method to draw the image has worked in the sense that the button is drawn showing the correct image. I'd like to improve it, though, by making its shape (clickable area) the same as the visible pixels on the image (right now if I draw the button's border, it's a square).

Is there an easy way to do that or do I have to parse the image and find the alpha pixels to make a custom border?

Which methods would I have to override to make it work the way I want?

Also, another question I'm going to have later: would it be better to use some kind of algorithm to change the images' colors to make it seem like it is being clicked when people click on it or am I better off creating a second image and drawing that one while the button is active?

Edit: I just read on some other question that I should redefine paintComponent() instead of paint(), I'd like to know why since redefining paint() works fine?

Edit 2: I changed everything to make sure my JButtons are created using the default constructor with an icon. What I'm trying to do is get the X and Y position of where the click was registered and grab the icon's pixel at that position and check its alpha channel to see if it is 0 (if it is, do nothing, else do the action it is supposed to do).

The thing is, the alpha channel always returns 255 (and blue, red and green are at 238 on transparent pixels). On other pixels, everything returns the value it should be returning.

Here's an example (try it with another image if you want) that recreates my problem:

public class TestAlphaPixels extends JFrame
{
  private final File FILECLOSEBUTTON = new File("img\\boutonrondX.png");  //My round button with transparent corners
  private JButton closeButton = new JButton(); //Creating it empty to be able to place it and resize the image after the button size is known


  public TestAlphaPixels() throws IOException
  {
    setLayout(null);
    setSize(150, 150);

    closeButton.setSize(100, 100);
    closeButton.setContentAreaFilled(false);
    closeButton.setBorderPainted(false);

    add(closeButton);

    closeButton.addMouseListener(new MouseListener()
      {

        public void mouseClicked(MouseEvent e)
        {
        }

        public void mousePressed(MouseEvent e)
        {
        }

        public void mouseReleased(MouseEvent e)
        {
          System.out.println("Alpha value of pixel (" + e.getX() + ", " + e.getY() + ") is: " + clickAlphaValue(closeButton.getIcon(), e.getX(), e.getY()));
        }

        public void mouseEntered(MouseEvent e)
        {
        }

        public void mouseExited(MouseEvent e)
        {
        }
      });
    Image imgCloseButton = ImageIO.read(FILECLOSEBUTTON);

    //Resize the image to fit the button
    Image newImg = imgCloseButton.getScaledInstance((int)closeButton.getSize().getWidth(), (int)closeButton.getSize().getHeight(), java.awt.Image.SCALE_SMOOTH);
    closeButton.setIcon(new ImageIcon(newImg));


  }

  private int clickAlphaValue(Icon icon, int posX, int posY) 
  {
    int width = icon.getIconWidth();
    int height = icon.getIconHeight();

    BufferedImage tempImage = (BufferedImage)createImage(width, height);
    Graphics2D g = tempImage.createGraphics();

    icon.paintIcon(null, g, 0, 0);

    g.dispose();

    int alpha = (tempImage.getRGB(posX, posY) >> 24) & 0x000000FF;

    return alpha;
  } 
  public static void main(String[] args)
  {
    try
    {
      TestAlphaPixels testAlphaPixels = new TestAlphaPixels();
      testAlphaPixels.setVisible(true);
      testAlphaPixels.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    catch(IOException ioe)
    {
      ioe.printStackTrace();
    }
  }
}

This is just a wild guess, but is it possible that when my image gets cast to an Icon, it loses its Alpha property and thus doesn't return the correct value? Anyway, I'd really appreciate it if someone could actually help me out and tell me what I should be changing to get the correct value.

I'm guessing that because when I try it with the original image, the alpha channel's value is fine, but I can't actually use that BufferedImage because I resize it, so I actually get the channel values of the image with the original size...

Kathline

If you want the button to just be the image, why not use a JLabel and set the image as its icon? – Hypogenous

The first reason is that I'm going to have some buttons that have text over the image generated from an array. The second one is that I didn't know that making it a JLabel would only draw the non-transparent pixels (and thus the alpha pixels wouldn't be considered as a click). I might try that, but I'd still have to code methods to draw it to make it seem like it is being clicked on. – Kathline

In regards to your second edit, why are you testing for alpha exactly? If this is to see if you clicked on a round button, there are much nicer ways of doing this and if that's the case I'll post it as an answer. Testing for alpha might come in handy only if the shapes aren't typical. (I see yours is round?) – Deutsch

@paranoid-android Your solution works fine and it will come in handy for sure. The thing is I'm going to have other odd shaped buttons in this program later, I just couldn't use them as example because I haven't created them yet, so the round buttons won't work on those. I'm probably going to use your method for the round buttons as it's a lot more simple, though Thanks! – Kathline

@Adam Smith: Glad to hear it. :) If you take that extension of JButton and start integrating Shapes, you're on the right track. Hope your app works out for you. – Deutsch

Answer 1

Since there were good elements in multiple answers, but none of the answers were complete on their own, I'll answer my own question so other people that have the same problem can try something similar.

I created my buttons using a new class which extends JButton, with a new constructor that takes a BufferedImage as parameter instead of an icon. The reason for that is that when I did something like myButton.getIcon(), it would return an Icon, then I'd have to make various manipulations on it to make it a BufferedImage of the right size, and it ended up not working anyway because it seems like the first cast to Icon made it lose the alpha data in the pixels, so I couldn't check to see if the user was clicking on transparent pixels or not.

So I did something like this for the constructor:

public class MyButton extends JButton
{
   private BufferedImage bufImg;

   public MyButton(BufferedImage bufImg)
   {
      super(new ImageIcon(bufImg));
      this.bufImg = bufImg;
   }
 }

Then I created an accessor for my bufImg that resized the image to fit the JButton using the getSize() method and then returned an image resized at the right size. I do the transformations in the getBufImg() accessor because the image size might change when the window gets resized. When you call the getBufImg(), it's usually because you clicked on the button and thus you're not currently resizing the window.

Something a little bit like this will return the image at the right size:

 public BufferedImage getBufImg()
    {
      BufferedImage newImg = new BufferedImage(getSize().getWidth(), getSize().getHeight(), BufferedImage.TYPE_INT_ARGB); //Create a new buffered image the right size
      Graphics2D g2d = newImg.createGraphics();
      g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);

      g2d.drawImage(bufImg, 0, 0, getSize().getWidth(), getSize().getHeight(), null);
      g2d.dispose();

      return newImg;
    }

With that buffered image, you can then code a method like this:

  private int clickAlphaValue(BufferedImage bufImg, int posX, int posY) 
  {
    int alpha;

    alpha = (bufImg.getRGB(posX, posY) >>24) & 0x000000FF; //Gets the bit that contains alpha information

    return alpha;
  }

That you call on the button that implements a MouseListener, like this:

myButton.addMouseListener(new MouseListener()
    {

    public void mouseClicked(MouseEvent e)
    {
    }

    public void mousePressed(MouseEvent e)
    {
    }

    public void mouseReleased(MouseEvent e)
    {
      if(clickAlphaValue(((myButton)e.getSource()).getBufImg(), e.getX(), e.getY()) != 0) //If alpha is not set to 0
        System.exit(0); //Or other things you want your button to do
    }

    public void mouseEntered(MouseEvent e)
    {
    }

    public void mouseExited(MouseEvent e)
    {
    }
  });

And voila! The button will only do the action if you clicked on non-transparent pixels.

Thanks for the help everyone, I couldn't have come up with this solutions on my own.

Kathline

Answer 2

I think you are on the wrong way. You do not have to override neither paint() nor paintComponent() methods. JButton already "knows" to be shown with image only:

ImageIcon cup = new ImageIcon("images/cup.gif");
JButton button2 = new JButton(cup);

See the following tutorial for example: http://www.apl.jhu.edu/~hall/java/Swing-Tutorial/Swing-Tutorial-JButton.html

Moreover swing is fully customized. You can control opacity, border, color etc. You probably should override some mentioned methods to change functionality. But in most cases there is better and simpler solution.

Puce

Answer 3

If you want to have shape-specific click points, you're better off using Shape and their contains method. If you want, you can create a shape when creating your custom button class as part of it, and implement a contains method by wrapping around the shape's contains method.

As for the custom JButton, create a class that extends JButton, like this:

import java.awt.*;
import javax.swing.*;

public class CustomButton extends JButton{

    /** Filename of the image to be used as the button's icon. */
    private String fileName;
    /** The width of the button */
    private int width;
    /** The height of the button. */
    private int height;

 public CustomButton(String fileName, int width, int height){
    this.fileName = fileName;
    this.width = width;
    this.height = height;
    createButton();
}

/**
 * Creates the button according to the fields set by the constructor.
 */
private void createButton(){
    this.setIcon(getImageIcon(filename));
    this.setPreferredSize(new Dimension(width, height));
    this.setMaximumSize(new Dimension(width, height));
    this.setFocusPainted(false);
    this.setRolloverEnabled(false);
    this.setOpaque(false);
    this.setContentAreaFilled(false);
    this.setBorderPainted(false);
    this.setBorder(BorderFactory.createEmptyBorder(0,0,0,0)); 
  }
}

Here's how you can load the ImageIcon, if you want to do it like this.

  public ImageIcon getImageIcon(String fileName){
    String imageDirectory = "images/"; //relative to classpath
    URL imgURL = getClass().getResource(imageDirectory + fileName);
    return new ImageIcon(imgURL);
  }

This will give you a button that will at least look like your image. I asked a similar question regarding Image-based events on click, and Shapes helped wonders. I guess it comes down to how complex your button images are. Here's reference anyway:
How can you detect a mouse-click event on an Image object in Java?

PS: Maybe look into generating shapes from images, that go around all the pixels that aren't transparent. No idea if this is possible, but it would mean that a button would only be "pressed" if the user clicks on the image part of it. Just a thought.

Deutsch

You may actually be able to do this without using Shape at all. See if setting an empty border makes only on-image clicks fire an ActionEvent. – Deutsch

Answer 4

If you want your button layout to be that of the non-transparent pixels in your image, then you should redefine the paintComponent() method. It is the most correct way of doing it (overriding paint() worked in old times but is now discouraged).

However I think it is not exactly what you want: you want a click on the button to be detected only if it is on a non-transparent pixel, right? In that case you have to parse your image and when clicked compare mouse coordinates to the pixel alpha channel of your image as JButton does not have such a feature.

Conradconrade

This approach seems overly complicated. – Hypogenous

Not that much, in java.awt.image there are classes that permit to access the RGB and alpha values for a pixel in an image. – Conradconrade

@Hypogenous What would be a good alternative solution? What Guillaume said seems exactly like what I'm looking for. I know you mentionned JLabels but will those register clicks on alpha pixels? If they do, I don't see how it could be less complicated than Guillaume's approach. – Kathline

This is the way I'm trying to implement right now, but some things don't work the way I want. If you can help me solve it I'll gladly mark your answer as accepted. – Kathline

Answer 5

paintComponent() instead of paint() depends if you paint() inside XxxButtonUI or just override paintComponent(), but there exists the option JButton#setIcon.

Tomika

Answer 6

If you have a round button, this is exactly what you need:

  public class RoundButton extends JButton {

       public RoundButton() {
         this(null, null);
      }
       public RoundButton(Icon icon) {
         this(null, icon);
      }
       public RoundButton(String text) {
         this(text, null);
      }
       public RoundButton(Action a) {
         this();
         setAction(a);
      }

       public RoundButton(String text, Icon icon) {
         setModel(new DefaultButtonModel());
         init(text, icon);
         if(icon==null) return;
         setBorder(BorderFactory.createEmptyBorder(0,0,0,0));
         setContentAreaFilled(false);
         setFocusPainted(false);
         initShape();
      }

    protected Shape shape, base;
    protected void initShape() {
      if(!getBounds().equals(base)) {
        Dimension s = getPreferredSize();
        base = getBounds();
        shape = new Ellipse2D.Float(0, 0, s.width, s.height);
      }
    }
    @Override public Dimension getPreferredSize() {
      Icon icon = getIcon();
      Insets i = getInsets();
      int iw = Math.max(icon.getIconWidth(), icon.getIconHeight());
      return new Dimension(iw+i.right+i.left, iw+i.top+i.bottom);
    }

    @Override public boolean contains(int x, int y) {
      initShape();
      return shape.contains(x, y);
      //or return super.contains(x, y) && ((image.getRGB(x, y) >> 24) & 0xff) > 0;
    }
  }

JButton has a contains() method. Override it and call it on mouseReleased();

Deutsch

why EmtpyBorder in your examples, btw +1 – Tomika

@mKorbel: Because any border that you might like should be included as part of your image to be used for the button. And I think it has something to do with cross-platform ActionEvent handling (when the button "activates" when you click on it), but I could be wrong about that. Really not sure, so don't take my word for it. – Deutsch

why not LineBorder ??? #5751811, that isn't attack to your person, my curiosity about ... – Tomika

We want to create a border, but make it effectively invisible by making it 0 wide etc. EmptyBorder is just the obvious choice. From the Java API: EmptyBorder: A class which provides an empty, transparent border which takes up space but does no drawing. – Deutsch

that isn't persuaded me, any way good idea with EmptyBorder, thank you – Tomika