Java Swing - 将透明度应用到透明组件上JPanel

Question

我正在创建支持透明度的JPanel，并且遇到问题，我不确定如何将相同级别的透明度应用于添加到所有Component的s这个面板。到目前为止我的代码：

package de.uebertreiberman.project.swing; 

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

import javax.swing.JPanel; 

@SuppressWarnings("serial") 
public class JTransparancyPanel extends JPanel { 

    float opacity = 1.0f; 

    /**Constructor for JTransparentPanel 
    */ 
    public JTransparancyPanel() 
    { 
     super(); 
     this.setOpaque(false); 
    } 

    /**Getter for opacity value of panel 
    * 
    * @return float containing opacity value of frame (0-1) 
    */ 
    public float getOpacity() 
    { 
     return opacity; 
    } 

    /**Setter for opacity value of panel 
    * 
    * @param value as float for opacity of frame (0-1) 
    */ 
    public void setOpacity(float value) 
    { 
     opacity = value; 
     repaint(); 
    } 

    /**Converts opacity value (0-1) to opacity color (0-255) 
    * 
    * @param opacity as float opacity value (0-1) 
    * @return integer containing converted opacity value (0-255) 
    */ 
    public static int getOpacityColor(float opacity) 
    { 
     return (int)(opacity * 255); 
    } 

    /**Converts opacity color (0-255) to opacity value (0-1) 
    * 
    * @param opacity as integer value (0-255) 
    * @return float containing converted opacity value (0-1) 
    */ 
    public static float getOpacityValue(int opacity) 
    { 
     //Returns more or less the correct, capped value 
     //Just ignore it, it works, leave it :D 
     return capFloat((3.9216f*opacity)/1000f, 0.0f, 1.0f); 
    } 

    /**Returns float capped between minimum and maximum value 
    * 
    * @param value as original value 
    * @param min as minimum cap value 
    * @param max as maximum cap value 
    * @return float containing capped value 
    */ 
    public static float capFloat(float value, float min, float max) 
    { 
     if(value < min) value = min; 
      else if(value > max) value = max; 

     return value; 
    } 

    /**Merges color and opacity to new color 
    * 
    * @param bg as color for old color, only RGB will be used from that 
    * @return color with RGB from bg and A from opacity of frame 
    */ 
    Color getTransparencyColor(Color bg) 
    { 
     return new Color(getOpacityValue(bg.getRed()), getOpacityValue(bg.getGreen()), getOpacityValue(bg.getBlue()), opacity); 
    } 

    @Override 
    public void paintComponent(Graphics g) 
    { 
     //Draw transparent background before painting other Components 
     g.setColor(getTransparencyColor(getBackground())); 
     Rectangle r = g.getClipBounds(); 
     g.fillRect(r.x, r.y, r.width, r.height); 

     //Paint other components 
     super.paintComponent(g); 
    } 
} 

的重要组成部分，基本上是在那里我overwride的paintComponent(Graphics g)方法结束。

我只需要backgroundcolor，将透明度应用于它并进行设置。

现在我想让这个面板的所有Component子元素都变得透明，我不太确定什么是最有效的方法。

你会建议什么？

Answer 1

我找到了一个解决方案 - 基本上我在评论中已经提到过：面板不是真的画在屏幕上。相反，它被绘制成图像，并且该图像被涂上适当的AlphaComposite。

（滑块可用于设置面板的不透明度）

虽然这种解决方案很简单，通用的，应该基本上是与所有的子组件工作，有一两件事我不喜欢它：有必要调整RepaintManager。为了确保应用面板的不透明性（并且子组件不是独立绘制的，并且具有完全不透明度），重绘管理器必须在子组件重新绘制时触发重新绘制整个组件。我想认为应该有没有这种解决方法的解决方案（例如，这可能是在面板上重写getGaphics可能是适当的罕见情况之一），但无济于事。也许通常的嫌疑人（camickr，Hovercraft等）找到更优雅和简洁的解决方案。

在那之前，这里是代码作为MCVE：

import java.awt.AlphaComposite; 
import java.awt.BorderLayout; 
import java.awt.Color; 
import java.awt.Component; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.image.BufferedImage; 

import javax.swing.JButton; 
import javax.swing.JComponent; 
import javax.swing.JFrame; 
import javax.swing.JLabel; 
import javax.swing.JPanel; 
import javax.swing.JSlider; 
import javax.swing.JTree; 
import javax.swing.RepaintManager; 
import javax.swing.SwingUtilities; 

public class TransparencyPanelTest 
{ 
    public static void main(String[] args) 
    { 
     SwingUtilities.invokeLater(() -> createAndShowGui()); 
    } 

    private static void createAndShowGui() 
    { 
     JFrame f = new JFrame(); 
     f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     f.getContentPane().setLayout(new BorderLayout()); 

     OpacityPanel opacityPanel = new OpacityPanel(); 

     opacityPanel.setLayout(new BorderLayout()); 
     opacityPanel.add(new JLabel("Label"), BorderLayout.NORTH); 
     opacityPanel.add(new JTree(), BorderLayout.CENTER); 
     opacityPanel.add(new JButton("Button"), BorderLayout.SOUTH); 

     f.getContentPane().add(opacityPanel, BorderLayout.CENTER); 

     JSlider slider = new JSlider(0, 100, 50); 
     slider.addChangeListener(e -> 
      opacityPanel.setOpacity(slider.getValue()/100.0f)); 
     f.getContentPane().add(slider, BorderLayout.SOUTH); 

     f.setSize(500,500); 
     f.setLocationRelativeTo(null); 
     f.setVisible(true); 
    } 

} 

class OpacityPanel extends JPanel 
{ 
    static 
    { 
     RepaintManager.setCurrentManager(new RepaintManager() 
     { 
      @Override 
      public void addDirtyRegion(
       JComponent c, int x, int y, int w, int h) 
      { 
       Component cc = c; 
       while (cc != null) 
       { 
        if (cc instanceof OpacityPanel) 
        { 
         OpacityPanel p = (OpacityPanel)cc; 
         super.addDirtyRegion(
          p, 0, 0, p.getWidth(), p.getHeight()); 
        } 
        cc = cc.getParent(); 
       } 
       super.addDirtyRegion(c, x, y, w, h); 
      } 
     }); 
    } 
    private float opacity = 0.5f; 
    private BufferedImage image; 

    public OpacityPanel() 
    { 
     setOpaque(false); 
    } 

    public void setOpacity(float opacity) 
    { 
     this.opacity = Math.max(0.0f, Math.min(1.0f, opacity)); 
     repaint(); 
    } 

    private void updateImage() 
    { 
     int w = Math.min(1, getWidth()); 
     int h = Math.min(1, getHeight()); 
     if (image == null || image.getWidth() != w || image.getHeight() != h) 
     { 
      image = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB); 
     } 
     Graphics2D g = image.createGraphics(); 
     g.setColor(new Color(0,0,0,0)); 
     g.setComposite(AlphaComposite.SrcOver); 
     g.fillRect(0, 0, w, h); 
     g.dispose(); 
    } 

    @Override 
    protected void paintComponent(Graphics gr) 
    { 
     updateImage(); 
     Graphics2D imageGraphics = image.createGraphics(); 
     super.paintComponent(imageGraphics); 
     imageGraphics.dispose(); 

     Graphics2D g = (Graphics2D) gr; 
     g.setComposite(AlphaComposite.getInstance(
      AlphaComposite.SRC_OVER, opacity)); 
     g.drawImage(image, 0, 0, null); 
    } 

}