Java Swing GlassPane 拖动性能

Question

我正在尝试使用 GlassPane 在 Swing 应用程序中进行可视化拖放，但遇到了拖动图像滞后于鼠标指针的问题，有时甚至相当严重。我该如何解决这个问题？我的 GlassPane 代码如下。谢谢!

package dragui;

import java.awt.*;
import javax.swing.*;
import java.awt.event.MouseEvent;
import javax.swing.event.MouseInputAdapter;

public class GlassPane extends JComponent {
    private int x=0, y=0, k=25,z=1;
    private boolean showDot;
    private MouseInputAdapter mia = new MouseInputAdapter(){

        @Override
        public void mouseDragged(MouseEvent me) {
            setPos(me.getX(), me.getY());
        }

        @Override
        public void mousePressed(MouseEvent me) {
            setShow(true);
            setPos(me.getX(), me.getY());   
        }

        @Override
        public void mouseReleased(MouseEvent me){
            setShow(false);
            setVisible(false);
        }
    };

    public void setShow(boolean b){ this.showDot = b; }

    public void paint(Graphics g) {
        if (showDot) {
            g.setColor(new Color(0.0f, 0.25f, 1.0f));
            g.fillOval(x - k, y - k, 2*k, 2*k);
        }
    }

    public void setPos(int x, int y) {
        int tmpX = this.x, tmpY = this.y; 
        this.x = x; this.y = y;
        repaint(tmpX - k , tmpY-k, 2*k+5, 2*k+5);
        repaint(this.x-k, this.y-k, 2*k+5, 2*k+5);        
    }

    public GlassPane() {
        addMouseListener(mia); 
        addMouseMotionListener(mia);
        setOpaque(false);
    }
}

Answer 1

根据Javadoc ,

A subclass that just wants to specialize the UI (look and feel) delegate's paint method should just override paintComponent.

这是因为 paint(...) 实际上将绘画工作委托(delegate)给了三个 protected 方法:paintComponent、paintBorder 和paintChildren。话虽这么说，请尝试用此替换 paint(...)

@Override
protected void paintComponent(Graphics g) {
    if (showDot) {
        Graphics gCopy = g.create();

        gCopy.setColor(new Color(0.0f, 0.25f, 1.0f));
        gCopy.fillOval(x - k, y - k, 2*k, 2*k);

        gCopy.dispose();
    }
}