Java AWT在半透明框架上绘制

我在半透明的画框上画画有困难。当“alphaValue”为255时，一切正常。但我需要一个半透明的框架。我在下面创建了一个小测试类来演示这个问题。如您所见，“中间”矩形始终出现。但“绘制”矩形仅在“alphaValue”为255时出现。当AWT组件本身没有透明度概念时，它们总是不透明的

您已经使用了

JPanel

，您可以使用

setOpaque

来控制不透明度（打开或关闭）。这将允许面板成为透明的，然后您应该能够看到直接应用到帧的alpha效果。。。

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您还可以混合重物和轻量级组件，可以考虑使用JPanel在面板上。它可能无法解决此问题，但可以防止其他可能的问题。我不认为面板有paintComponent方法。如果alpha值为254，我认为我仍然会看到一个绘制的矩形，而不是什么都没有。使用像

Panel

这样的重量级组件可能是问题的“一部分”。我想问你为什么使用AWT组件直接对我来说效果很好（alpha设置为128），当我拖动鼠标左右时，我可以看到

PAINT

和

DRAW

，只需切换到JFrame和JPanel即可。我实现了这个组件。如何使矩形不透明（alpha 255）。如果帧是setOpacity（.1）。先生，您是一个向导，我希望我能给您多投一票。

import java.awt.Color;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Panel;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

public class TransparencyTest {
    private static Point startPoint = new Point();
    private static Point endPoint = new Point();

    public static void main(String[] args) {
        new TransparencyTest().test();
    }

    @SuppressWarnings("serial")
    private void test() {
        int alphaValue = 255;

        Frame myFrame = new Frame();
        myFrame.setUndecorated(true);
        myFrame.setBackground(new Color(0, 0, 0, alphaValue));
        myFrame.setSize(800, 800);

        Panel myPanel = new Panel() {
            public void paint(Graphics g) {
                super.paint(g);
                System.out.println("PAINT");
                g.setColor(new Color(255, 0, 0, 255));
                if(startPoint.equals(new Point())) {
                    System.out.println("MIDDLE");
                    g.drawRect(200, 200, 400, 400);
                }
                else {
                    System.out.println("DRAW");
                    g.drawRect(
                            (int)Math.min(startPoint.getX(), endPoint.getX()),
                            (int)Math.min(startPoint.getY(), endPoint.getY()),
                            (int)Math.abs(startPoint.getX() - endPoint.getX()),
                            (int)Math.abs(startPoint.getY() - endPoint.getY())
                    );
                }
            }
        };
        myFrame.add(myPanel);

        MouseAdapter myMouseAdapter = new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                startPoint = e.getPoint();
            }

            public void mouseDragged(MouseEvent e) {
                endPoint = e.getPoint();
                myPanel.repaint();
            }
        };
        myPanel.addMouseListener(myMouseAdapter);
        myPanel.addMouseMotionListener(myMouseAdapter);

        myFrame.setVisible(true);
    }
}

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TransparencyTest {

    private static Point startPoint = new Point();
    private static Point endPoint = new Point();

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                new TransparencyTest().test();
            }
        });
    }

    @SuppressWarnings("serial")
    private void test() {
        int alphaValue = 128;

        JFrame myFrame = new JFrame();
        myFrame.setUndecorated(true);
        myFrame.setBackground(new Color(0, 0, 0, alphaValue));
//      myFrame.setOpacity(0.1f);
        myFrame.setSize(800, 800);
        myFrame.setLocation(100, 100);

        JPanel myPanel = new JPanel() {
            public void paintComponent(Graphics g) {
                super.paintComponent(g);

                System.out.println("PAINT");
                g.setColor(new Color(255, 0, 0, 255));
                if (startPoint.equals(new Point())) {
                    System.out.println("MIDDLE");
                    g.drawRect(200, 200, 400, 400);
                } else {
                    System.out.println("DRAW");
                    g.drawRect(
                            (int) Math.min(startPoint.getX(), endPoint.getX()),
                            (int) Math.min(startPoint.getY(), endPoint.getY()),
                            (int) Math.abs(startPoint.getX() - endPoint.getX()),
                            (int) Math.abs(startPoint.getY() - endPoint.getY())
                    );
                }
            }
        };
        myPanel.setOpaque(false);
        myFrame.add(myPanel);

        MouseAdapter myMouseAdapter = new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                startPoint = e.getPoint();
            }

            public void mouseDragged(MouseEvent e) {
                endPoint = e.getPoint();
                myPanel.repaint();
            }
        };
        myPanel.addMouseListener(myMouseAdapter);
        myPanel.addMouseMotionListener(myMouseAdapter);

        myFrame.setVisible(true);
    }
}