Implementing Cursor in Java with some Transparency

Question

I have a 35x40 px. png image I want to use as a custom cursor in a Swing application. The image has a glow so contains alpha transparency values. Problem is when I attempt to use the conventional method of using the Toolkit to generate the custom cursor I get black pixels where alpha transparency values should be.

Here is the image I am using for a cursor: https://dl.dropbox.com/u/1186703/cursor.png

Here is my code:

public static void main(String[] args) throws IOException {

     new Sandbox().gui();

}
private Cursor cursor;

private Toolkit kit;

private Image cursorImage;

public void gui() {

    kit = Toolkit.getDefaultToolkit();
    cursorImage = kit.createImage(getClass().getResource(
            "/aurora/V1/resources/cursor.png"));

    cursor = Toolkit.getDefaultToolkit().createCustomCursor(
            cursorImage, new Point(0, 0), "CustomCursor");

    setSize(800, 800);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setLocationRelativeTo(null);
    setVisible(true);
    setCursor(cursor);
}

Here is the current result:

Edit it seems that this method does not work well cross platform, for instance Windows LAF doesn't support semi-transparency. I am therefore looking for any solution to get this to work on windows, assuming this implementation does work on Mac OSX, i can just specify in code which implementation to use based on which operating system the app is running on.

Answer 1

The problem your having is to do with the Cursor class which (under Windows) doesn't take into account the transparency values of the image

This is, by no means, a "real" solution, but is more about "fudging" the result...

public class TestMouseCursor {

    public static void main(String[] args) {
        new TestMouseCursor();
    }

    public TestMouseCursor() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new MouseCursorPane());
                frame.setSize(400, 400);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class MouseCursorPane extends JPanel {

        private BufferedImage cursorImage;
        private Toolkit kit;

        public MouseCursorPane() {
            try {
                kit = Toolkit.getDefaultToolkit();
                cursorImage = ImageIO.read(getClass().getResource("/cursor02.png"));
                for (int i = 0; i < cursorImage.getHeight(); i++) {
                    int[] rgb = cursorImage.getRGB(0, i, cursorImage.getWidth(), 1, null, 0, cursorImage.getWidth() * 4);
                    for (int j = 0; j < rgb.length; j++) {
                        int alpha = (rgb[j] >> 24) & 255;
                        if (alpha < 128) {
                            alpha = 0;
                        } else {
                            alpha = 255;
                        }
                        rgb[j] &= 0x00ffffff;
                        rgb[j] = (alpha << 24) | rgb[j];
                    }
                    cursorImage.setRGB(0, i, cursorImage.getWidth(), 1, rgb, 0,
                            cursorImage.getWidth() * 4);
                }
                Cursor cursor = Toolkit.getDefaultToolkit().createCustomCursor(
                        cursorImage, new Point(0, 0), "CustomCursor");

                setCursor(cursor);

            } catch (Exception exp) {
                exp.printStackTrace();
            }
        }
    }
}

I got the idea for here