Question

I am trying to build a program that detects the color that is under the mouse cursor and then displays the color and RGB values in a window on the screen. I am VERY new to Java so do not know much of anything. I have two codes I have worked on, with help from a friend, The first one gets the RGB values of a specific coordinate of a buffered image, and the other takes user defined RGB values and shows a pane with the color in it. My question is “how do I get the program to detect the color under the mouse cursor no matter what it is scrolling over?

public class Buffered_Image 
{
public static void main(String[] args) throws IOException 
{
    BufferedImage bi = ImageIO.read(new File("C:/Users/user/Pictures/Hornet.jpg"));
    Color c = new Color(bi.getRGB(50,40));
    int red=c.getRed();
    int green=c.getGreen();
    int blue=c.getBlue();

    System.out.print("Red " + red + " Green " + green+ " Blue" + blue + "\n" );
}
}




public class RGB_Pane 
{

public static void main(String[] args) 
{
    JFrame F = new JFrame("RGB");
    Panel Pan = new Panel();
    F.getContentPane().add(Pan);
    F.pack();
    F.setVisible(true);
    F.setSize(300, 300);
}
}

class Panel extends JPanel
{
public Panel()
{ 
    setPreferredSize(new Dimension(200,200));
    int Red = Integer.parseInt(JOptionPane.showInputDialog("Enter value for RED"));
    int Green = Integer.parseInt(JOptionPane.showInputDialog("Enter value for Green"));
    int Blue = Integer.parseInt(JOptionPane.showInputDialog("Enter value for BLUE"));
    Color Defined_Color = new Color(Red,Green,Blue);
    setBackground(Defined_Color);
}
}

Answer 1

As @Hovercraft has pointed out.

Start by looking at Robot#getPixelColor.

You will need to know where the mouse cursor is, while there’s no “easy” way to track the cursor, you can get it’s current location using MouseInfo#getPointerInfo

UPDATED with example

This is little example of the concept. This works based on the moition of the mouse cursor. A possible enhancement would be to also notify the monitor listener when the color changes under the cursor as well…

public class WhatsMyColor {

    public static void main(String[] args) throws IOException {
        new WhatsMyColor();
    }

    public WhatsMyColor() {
        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) {
                }

                try {
                    JFrame frame = new JFrame();
                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                    frame.setLayout(new BorderLayout());
                    frame.add(new MouseColorPane());
                    frame.setSize(400, 200);
                    frame.setLocationRelativeTo(null);
                    frame.setVisible(true);
                } catch (Exception exp) {
                    exp.printStackTrace();
                }

            }
        });
    }

    public class MouseColorPane extends JPanel implements MouseMonitorListener {

        private Robot robot;

        private JLabel label;

        public MouseColorPane() throws AWTException {

            label = new JLabel();

            setLayout(new GridBagLayout());
            add(label);

            robot = new Robot();
            PointerInfo pi = MouseInfo.getPointerInfo();
            updateColor(pi.getLocation());
            MouseMonitor monitor = new MouseMonitor();
            monitor.setMouseMonitorListener(this);
            monitor.start();

        }

        protected void updateColor(Point p) {

            Color pixelColor = robot.getPixelColor(p.x, p.y);
            setBackground(pixelColor);

            label.setText(p.x + "x" + p.y + " = " + pixelColor);

        }

        @Override
        public void mousePositionChanged(final Point p) {
            SwingUtilities.invokeLater(new Runnable() {

                @Override
                public void run() {
                    updateColor(p);
                }

            });
        }
    }

    public interface MouseMonitorListener {

        public void mousePositionChanged(Point p);
    }

    public static class MouseMonitor extends Thread {

        private Point lastPoint;
        private MouseMonitorListener listener;

        public MouseMonitor() {
            setDaemon(true);
            setPriority(MIN_PRIORITY);
        }

        public void setMouseMonitorListener(MouseMonitorListener listener) {
            this.listener = listener;
        }

        public MouseMonitorListener getMouseMonitorListener() {
            return listener;
        }

        protected Point getMouseCursorPoint() {
            PointerInfo pi = MouseInfo.getPointerInfo();
            return pi.getLocation();
        }

        @Override
        public void run() {
            lastPoint = getMouseCursorPoint();
            while (true) {
                try {
                    sleep(250);
                } catch (InterruptedException ex) {
                }

                Point currentPoint = getMouseCursorPoint();
                if (!currentPoint.equals(lastPoint)) {
                    lastPoint = currentPoint;
                    MouseMonitorListener listener = getMouseMonitorListener();
                    if (listener != null) {
                        listener.mousePositionChanged((Point) lastPoint.clone());
                    }
                }

            }
        }
    }
}