使用frame.setBackground（0,255,0,0）不能与linux一起使用

Question

所以我通过将背景alpha设置为0来使JFrame背景变得透明，但是如果我在linux中运行程序，JFrame背景是白色的，为什么会这样呢？

好吧我发现它与渲染图形到框架有关，这个方法很旧我不再需要它在程序中但我仍然想知道为什么会发生这种情况（它只是在Linux中找到了视窗）

这是一个可运行的例子

import java.awt.*;
import java.awt.Color;
import javax.swing.*;

class Main extends JFrame{
private void init() {

    this.setPreferredSize(new Dimension(1420, 820));
    this.setUndecorated(true);
    this.setResizable(false);
    this.setDefaultCloseOperation(this.EXIT_ON_CLOSE);
    this.setBackground(new Color(0, 255, 0, 0));
    this.requestFocus();
    this.setVisible(true);
    this.validate();
    this.pack();
    Color color = UIManager.getColor("activeCaptionBorder");
    this.getRootPane().setBorder(BorderFactory.createLineBorder(color, 1));
    paintInfo();
}

private void paintInfo() {
    Graphics g = this.getGraphics();
    g.setColor(new Color(222, 222, 222, 4));
    g.setFont(new Font("Arial Black", Font.BOLD, 15));
    g.setColor(Color.BLACK);
    g.drawString("test String ",this.getWidth()/2, this.getHeight()/2);
    g.dispose();
}

public static void main(String[] args) {
    JFrame.setDefaultLookAndFeelDecorated(true);
    new Main().init();
}
}

Answer 1

让我们从...开始......

private void paintInfo() {
    Graphics g = this.getGraphics();
    g.setColor(new Color(222, 222, 222, 4));
    g.setFont(new Font("Arial Black", Font.BOLD, 15));
    g.setColor(Color.BLACK);
    g.drawString("test String ",this.getWidth()/2, this.getHeight()/2);
    g.dispose();
}

不是如何在Swing中完成绘画并处理你没有创建的Graphics上下文会导致奇怪的事情......

相反，创建你的框架，设置它的透明度，然后添加另一个组件，它可以做你想要的实际绘画，例如......

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.GridBagLayout;
import java.awt.LinearGradientPaint;
import java.awt.Point;
import java.awt.Rectangle;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

/**
 *
 * @author swhitehead
 */
public class JavaApplication233 {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        GraphicsEnvironment ge
                        = GraphicsEnvironment.getLocalGraphicsEnvironment();
        GraphicsDevice gd = ge.getDefaultScreenDevice();

        //If translucent windows aren't supported, exit.
        if (!gd.isWindowTranslucencySupported(GraphicsDevice.WindowTranslucency.PERPIXEL_TRANSLUCENT)) {
            System.err.println("Per-pixel translucency is not supported");
            System.exit(0);
        } else {
            new JavaApplication233();
        }
    }

    public JavaApplication233() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setUndecorated(true);
                frame.setBackground(new Color(0, 0, 0, 0));
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setOpaque(false);
            setLayout(new GridBagLayout());
            add(new JLabel("I'm not wearing anything"));
//          Color color = UIManager.getColor("activeCaptionBorder");
            setBorder(BorderFactory.createLineBorder(Color.BLACK, 1));
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            LinearGradientPaint lgp = new LinearGradientPaint(
                            new Point(0, 0),
                            new Point(0, getHeight()),
                            new float[]{0f, 1f},
                            new Color[]{applyAlpha(Color.RED), applyAlpha(Color.YELLOW)}
            );
            g2d.setPaint(lgp);
            g2d.fill(new Rectangle(0, 0, getWidth(), getHeight()));
            g2d.dispose();
        }

        protected Color applyAlpha(Color color) {
            return new Color(color.getRed(), color.getGreen(), color.getBlue(), 64);
        }

    }

}