我想让JFrame的一部分透明。它应该看起来像OneNote屏幕剪辑器。我基本上有一个全屏叠加的部分透明的JFrame,然后在这个JFrame里面,我想通过拖动鼠标制作一些矩形,并使这些矩形完全透明,就像这样:
---------------------------------------
| partially transparent |
| |
| ----------- |
| | fully | |
| | transp. | |
| ----------- |
----------------------------------------
我该怎么做?目前我有以下内容:
public class Overlay extends JFrame implements MouseMotionListener, MouseListener {
private Rectangle2D.Double selection;
private Point start;
private Point end;
public Overlay() {
addMouseMotionListener(this);
addMouseListener(this);
setSize(Toolkit.getDefaultToolkit().getScreenSize());
setAlwaysOnTop(true);
setUndecorated(true);
setOpacity(0.2f);
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
@Override
public void paint(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g2d.clearRect(0, 0, getWidth(), getHeight());
if (selection != null) {
Area outside = new Area(new Rectangle2D.Double(0, 0, getWidth(), getHeight()));
outside.subtract(new Area(selection));
g2d.setClip(outside);
g2d.setColor(new Color(0.5f,0.5f,0.5f, 0.5f));
g2d.fillRect(0, 0, getWidth(), getHeight());
}
@Override
public void mousePressed(MouseEvent e) {
start = e.getLocationOnScreen();
}
@Override
public void mouseDragged(MouseEvent e) {
end = e.getLocationOnScreen();
selection = new Rectangle2D.Double(start.x, start.y, end.x - start.x, end.y - start.y);
repaint();
}
}
但是这种方法并不正确,因为它会多次重绘背景,导致背景变得更暗/透明度降低,并且速度非常慢... 重绘需要很长时间,而且非常明显。
paint
,而是覆盖paintComponent()
。如果您没有实现所有方法,请使用适配器而不是监听器。 - user1803551