java 为什么 MouseEvent 的 getX() getY() 似乎偏离了真实坐标？
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Why does the getX() getY() of MouseEvent seem to offset from the real coordinate?
提问by AppleGrew
I have a JPanelembedded inside a JFrame. JPanelis added at CENTERof 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?
我有一个JPanel嵌入在JFrame. JPanel在加入CENTER的BorderLayout。我正在使用以下代码在其上绘制，但MouseEvent'sgetX()和getY()似乎偏移了真实坐标。为什么？
The relevant code is:-
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);
}
回答by Andreas Dolk
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.
也许您已将鼠标侦听器添加到 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。
