CODEWITHSUNDEEP
javaswing
AppleGrew
AppleGrew

Reputation: 9570

Why does the getX() getY() of MouseEvent seem to offset from the real coordinate?

I have a JPanel embedded inside a JFrame. JPanel is added at CENTER of BorderLayout. I am using the following code to draw on it but the MouseEvent's getX() and getY() seem to offset the real coordinate. Why?

The relevant code is:-

private Image backBuffer = createImage(getWidth(), getHeight());

public void mouseDragged(MouseEvent e) {
    //System.out.println("Canvas.mouseDragged()");
    Graphics2D g2d = (Graphics2D) backBuffer.getGraphics();
    int x = e.getX(), y = e.getY();
    if(lastCoord == null) {
        g2d.drawRect(x, y, 0, 0);
    } else {
        g2d.drawLine(lastCoord[0], lastCoord[1], x, y);
    }
    lastCoord = new Integer[]{x, y};
    repaint();
}

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D graphics2D = (Graphics2D) g;
    graphics2D.setColor(Color.black);
    graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
        RenderingHints.VALUE_ANTIALIAS_ON);
    graphics2D.drawImage(backBuffer, 0, 0, null);
}

What I mean by offset

Upvotes: 7

Views: 14019

Answers (1)

Andreas Dolk
Andreas Dolk

Reputation: 114767

Maybe you've added your mouse listener to the JFrame (and not to the panel) so getX and getY values are relative to the JFrame. Then the offsets are the JFrame borders and upper title bar.

Upvotes: 13

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