Java Swing - applying transparency to components on a transparent JPanel

Question

I am working on a creation JPanelthat supports transparency, and came to this problem that I am not sure how to apply the same level of transparency to all Componentadded to this panel. My code is:

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);
    }
}

The important part is mainly at the end, where I rewrite the method paintComponent(Graphics g).

I just take it backgroundcolor, apply transparency to it and set it.

Now I want all the Component children of this panel to become transparent, and I'm not quite sure what would be the most efficient way to do this.

What would you suggest?

Answer 1

- , : . , AlphaComposite.

( )

, , , : RepaintManager. , ( ), , . , (, , getGaphics ), . , (camickr, Hovercraft ..) .

, 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);
    }

}