如何设置JPanel的透明背景？

Question

可以将JPanel背景设置为透明吗？

我的框架有两个JPanels:

• 图像面板和
• 功能面板.

功能面板与图像面板重叠.所述图像面板正在作为后台和它从远程URL加载图像.

在功能面板上我想绘制形状.由于功能面板的背景颜色,现在无法看到图像面板.

我需要使功能面板背景透明,同时仍然绘制其形状,我希望图像面板可见(因为它正在进行图像的平铺和缓存功能).

我正在使用两个JPanel,因为我需要分离图像和形状绘图.

有没有办法重叠Jpanel有透明背景？

Answer 1

打电话setOpaque(false)给鞋帮JPanel应该有效.

从你的评论中,听起来像Swing绘画可能在某处被打破 -

首先 - 你可能想要覆盖paintComponent()而不是覆盖paint()你所paint()覆盖的任何组件.

第二 - 当你覆盖时paintComponent(),你首先想要先调用super.paintComponent()所有默认的Swing绘画内容(其中尊重setOpaque()是一个).

示例 -

import java.awt.Color;
import java.awt.Graphics;

import javax.swing.JFrame;
import javax.swing.JPanel;


public class TwoPanels {
    public static void main(String[] args) {

        JPanel p = new JPanel();
        // setting layout to null so we can make panels overlap
        p.setLayout(null);

        CirclePanel topPanel = new CirclePanel();
        // drawing should be in blue
        topPanel.setForeground(Color.blue);
        // background should be black, except it's not opaque, so 
        // background will not be drawn
        topPanel.setBackground(Color.black);
        // set opaque to false - background not drawn
        topPanel.setOpaque(false);
        topPanel.setBounds(50, 50, 100, 100);
        // add topPanel - components paint in order added, 
        // so add topPanel first
        p.add(topPanel);

        CirclePanel bottomPanel = new CirclePanel();
        // drawing in green
        bottomPanel.setForeground(Color.green);
        // background in cyan
        bottomPanel.setBackground(Color.cyan);
        // and it will show this time, because opaque is true
        bottomPanel.setOpaque(true);
        bottomPanel.setBounds(30, 30, 100, 100);
        // add bottomPanel last...
        p.add(bottomPanel);

        // frame handling code...
        JFrame f = new JFrame("Two Panels");
        f.setContentPane(p);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(300, 300);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    // Panel with a circle drawn on it.
    private static class CirclePanel extends JPanel {

        // This is Swing, so override paint*Component* - not paint
        protected void paintComponent(Graphics g) {
            // call super.paintComponent to get default Swing 
            // painting behavior (opaque honored, etc.)
            super.paintComponent(g);
            int x = 10;
            int y = 10;
            int width = getWidth() - 20;
            int height = getHeight() - 20;
            g.drawArc(x, y, width, height, 0, 360);
        }
    }
}

Answer 2

或者,请考虑" 如何使用根窗格 "一文中讨论的"玻璃窗格".您可以在玻璃窗格的paintComponent()方法中绘制"特征"内容.

附录:使用GlassPaneDemo,我添加了一个图像:

//Set up the content pane, where the "main GUI" lives.
frame.add(changeButton, BorderLayout.SOUTH);
frame.add(new JLabel(new ImageIcon("img.jpg")), BorderLayout.CENTER);

并改变了玻璃窗格的paintComponent()方法:

protected void paintComponent(Graphics g) {
    if (point != null) {
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(
            RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.setComposite(AlphaComposite.getInstance(
            AlphaComposite.SRC_OVER, 0.3f));
        g2d.setColor(Color.yellow);
        g2d.fillOval(point.x, point.y, 120, 60);
    }
}

如前所述这里,Swing组件必须履行的不透明财产 ; 在此变体中,ImageIcon完全填充BorderLayout.CENTER框架的默认布局.

Answer 3

在我的特定情况下,这样做更容易:

 panel.setOpaque(true);
 panel.setBackground(new Color(0,0,0,0,)): // any color with alpha 0 (in this case the color is black

Answer 4

(Feature Panel).setOpaque(false);

希望这可以帮助。