为什么MouseEvent的getX()getY()似乎偏离了真实坐标？

Question

我有一个JPanel嵌入式内部JFrame.JPanel是添加CENTER的BorderLayout.我使用下面的代码借鉴它,但MouseEvent的getX(),并getY()似乎抵消了真正的协调.为什么？

相关代码是: -

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);
}

Answer 1

也许你已经将鼠标监听器添加到JFrame(而不是面板),因此getX和getY值是相对于JFrame的.然后偏移量是JFrame边框和上标题栏.