GradientPanel.java :  » Rule-Engine » zilonis » org » zilonis » tool » ui » Java Open Source

package org.zilonis.tool.ui;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.LayoutManager;
import java.awt.Rectangle;
import java.awt.Shape;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;

import javax.swing.JPanel;

public class GradientPanel extends JPanel {
    protected BufferedImage gradientImage;
    protected Color gradientStart = new Color(110, 110, 110);
    protected Color gradientEnd = new Color(0, 0, 0);

    public GradientPanel() {
        this(new BorderLayout());
    }

    public GradientPanel(LayoutManager layout) {
        super(layout);
        addComponentListener(new GradientCacheManager());
    }

    @Override
  protected void paintComponent(Graphics g) {
        createImageCache();

        if (gradientImage != null) {
            Shape clip = g.getClip();
            Rectangle bounds = clip.getBounds();

            Image backgroundImage = gradientImage.getSubimage(bounds.x,
                                                              bounds.y,
                                                              bounds.width,
                                                              bounds.height);
            g.drawImage(backgroundImage, bounds.x, bounds.y, null);
        }
  }

    protected void createImageCache() {
        int width = getWidth();
        int height = getHeight();

        if (width == 0 || height == 0) {
            return;
        }

        if (gradientImage == null ||
            width != gradientImage.getWidth() || 
            height != gradientImage.getHeight()) {
         
            gradientImage = new BufferedImage(width, height,
                                              BufferedImage.TYPE_INT_RGB);
        
            Graphics2D g2 = gradientImage.createGraphics();
            GradientPaint painter = new GradientPaint(0, 0, gradientEnd,
                                                      0, height / 2, gradientStart);
            g2.setPaint(painter);
            Rectangle2D rect = new Rectangle2D.Double(0, 0, width, height / 2.0);
            g2.fill(rect);

            painter = new GradientPaint(0, height / 2, gradientStart,
                                        0, height, gradientEnd);
            g2.setPaint(painter);
            rect = new Rectangle2D.Double(0, (height / 2.0) - 1.0, width, height);
            g2.fill(rect);
            
            g2.dispose();
        }
    }

    private void disposeImageCache() {
        synchronized (gradientImage) {
            gradientImage.flush();
            gradientImage = null;
        }
    }
    
    private class GradientCacheManager implements ComponentListener {
        public void componentResized(ComponentEvent e) {
        }

        public void componentMoved(ComponentEvent e) {
        }

        public void componentShown(ComponentEvent e) {
        }

        public void componentHidden(ComponentEvent e) {
            disposeImageCache();
        }

    }
}