Graphics 2D and Components

[Gregg Bolinger]

Are there any 3rd party components out there that let you issue Graphics2D drawing commands outside of the paint() method? Or are we always stuck with overriding this method and issuing all commands there?

[Nathan Pruett]

All you have to do is cast getGraphics() to Graphics2D and use it normally. However, it's always better to do this in the paint method because that's what gets called in the redraw loop built in to Swing.

I guess you could create a BuffedImage to draw to and have the component reference the same BufferedImage in it's paint() method. You'd still have to remember to call repaint() every time you made changes, though...

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.image.BufferedImage;
import javax.swing.JComponent;
import javax.swing.JFrame;
 
public class DrawComponent extends JComponent {
    
    private BufferedImage image;
    
    public void paint( Graphics g ) {
        if ( image == null ) {
            image = new BufferedImage( getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB );
        }
        if ( image.getWidth() != getWidth() || image.getHeight() != getHeight() ) {
            BufferedImage temp = new BufferedImage( getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB );
            Graphics tg = temp.getGraphics();
            tg.drawImage( image, 0, 0, this );
            tg.dispose();
            image = temp;
        }
        g.drawImage( image, 0, 0, this );
        g.setColor( Color.black );
        g.drawRect( 0, 0, getWidth(), getHeight() );
    }
    
    public Graphics2D getGraphics2D() {
        if ( image == null ) {
            image = new BufferedImage( getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB );
        }
        return (Graphics2D)image.getGraphics();
    }
    
    public static void main(String[] args) {
        JFrame f = new JFrame( "DrawComponent Test" );
        final DrawComponent dc = new DrawComponent();
        dc.addMouseMotionListener( new MouseMotionAdapter() {
            public void mouseMoved( MouseEvent e ) {
                Graphics2D g = dc.getGraphics2D();
                g.drawOval( e.getX() - 5, e.getY() - 5, 10, 10 );
                dc.repaint();
            }
        } );
        f.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        f.getContentPane().add( dc );
        f.setSize( 200, 200 );
        f.setVisible( true );
    }
}

If you explain what exactly are you trying to do I might be able to offer more direction.