How to smoothen scrolling of JFrame in Java

Question

I have a JFrame in my Java application that contains a JPanel where I have some drawing objects created at run-time. The problem is while scrolling the JF

Answer 1

Part 1

There are my little mods on mKorbel's answer, thanks to him and Gilbert Le Blanc :

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.LayoutManager;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.lang.ref.WeakReference;
import java.util.Random;
import javax.swing.Scrollable;
import javax.swing.SwingConstants;
import javax.swing.Timer;


/**
 *
 * @author leBenj
 */
public class GJPanelBufferedImageTileAdapter extends GJPanelBufferedImageAdapter implements Scrollable
{
    protected BufferedImage _image = null;

    protected GIPanelListener _parent = null;

    private int TILE_SIZE_W = -1;

    private int TILE_SIZE_H = -1;

    private int TILE_COUNT_W = 32;

    private int TILE_COUNT_H = 32;

    private int visibleTiles = 10;

    private boolean[][] loading;

    private WeakReference[][] subs;

    private final Random random;

    public GJPanelBufferedImageTileAdapter( final GIPanelListener parent , LayoutManager layout , boolean isDoubleBuffered )
    {
        super( parent , layout , isDoubleBuffered );
        this._parent = parent;
        resetTiling();
        random = new Random();
    }

    public void resetTiling()
    {
        loading = new boolean[TILE_COUNT_W][TILE_COUNT_H];
        subs = new WeakReference[TILE_COUNT_W][TILE_COUNT_H];
    }

    private BufferedImage getTile( int x , int y )
    {
        BufferedImage retour = null;
        if( x < TILE_COUNT_W )
        {
            if( y < TILE_COUNT_H )
            {
                if( subs[x][y] != null )
                {
                    retour = subs[x][y].get();
                }
            }
        }
        return retour;
    }

    private void setTile( BufferedImage sub , int x , int y )
    {
        subs[x][y] = new WeakReference( sub );
    }

    private boolean loadTile( final int x , final int y )
    {
        boolean canPaint = ( getTile( x , y ) != null );
        if( x < TILE_COUNT_W )
        {
            if( y < TILE_COUNT_H )
            {
                if( !canPaint && !loading[x][y] )
                {
                    Timer timer = new Timer( random.nextInt( 500 ) , new ActionListener()
                    {
                        @Override
                        public void actionPerformed( ActionEvent e )
                        {
                            BufferedImage sub = _image.getSubimage( x * TILE_SIZE_W , y * TILE_SIZE_H , TILE_SIZE_W , TILE_SIZE_H );
                            setTile( sub , x , y );
                            repaint( x * TILE_SIZE_W , y * TILE_SIZE_H , TILE_SIZE_W , TILE_SIZE_H );
                        }
                    } );
                    timer.setRepeats( false );
                    timer.start();
                }
            }
        }
        return canPaint;
        }

    // using paint(g) instead of paintComponent(g) to start drawing as soon as the panel is ready
    @Override
    protected void paint( Graphics g )
    {
        super.paint( g );
        Rectangle clip = g.getClipBounds();
        int startX = clip.x - ( clip.x % TILE_SIZE_W );
        int startY = clip.y - ( clip.y % TILE_SIZE_H );
        int endX = clip.x + clip.width /*- TILE_SIZE_W*/;
        int endY = clip.y + clip.height /*- TILE_SIZE_H*/;
        for( int x = startX ; x < endX ; x += TILE_SIZE_W )
        {
            for( int y = startY ; y < endY ; y += TILE_SIZE_H )
            {
                if( loadTile( x / TILE_SIZE_W , y / TILE_SIZE_H ) )
                {
                    BufferedImage tile = getTile( x / TILE_SIZE_W , y / TILE_SIZE_H );
                    if( tile != null )
                    {
                        g.drawImage( subs[x / TILE_SIZE_W][y / TILE_SIZE_H].get() , x , y , this );
                    }
                }
                else
                {
                    g.setColor( Color.RED );
                    g.fillRect( x , y , TILE_SIZE_W - 1 , TILE_SIZE_H - 1 );
                }
            }
        }
            g.dispose(); // Without this, the original view area will never be painted
    }

    /**
     * @param image the _image to set
     */
    public void setImage( BufferedImage image )
    {
        this._image = image;
        TILE_SIZE_W = _image.getWidth() / TILE_COUNT_W;
        TILE_SIZE_H = _image.getHeight() / TILE_COUNT_H;
        setPreferredSize( new Dimension( TILE_SIZE_W * TILE_COUNT_W , TILE_SIZE_H * TILE_COUNT_H ) );
    }

    @Override
    public Dimension getPreferredScrollableViewportSize()
    {
        return new Dimension( visibleTiles * TILE_SIZE_W , visibleTiles * TILE_SIZE_H );
    }

    @Override
    public int getScrollableBlockIncrement( Rectangle visibleRect , int orientation , int direction )
    {
        if( orientation == SwingConstants.HORIZONTAL )
        {
            return TILE_SIZE_W * Math.max( 1 , visibleTiles - 1 );
        }
        else
        {
            return TILE_SIZE_H * Math.max( 1 , visibleTiles - 1 );
        }
    }

    @Override
    public boolean getScrollableTracksViewportHeight()
    {
        return false;
    }

    @Override
    public boolean getScrollableTracksViewportWidth()
    {
        return false;
    }

    @Override
    public int getScrollableUnitIncrement( Rectangle visibleRect , int orientation , int direction )
    {
        if( orientation == SwingConstants.HORIZONTAL )
        {
            return TILE_SIZE_W;
        }
        else
        {
            return TILE_SIZE_H;
        }
    }

}

Explanations :

There was a little problem on right and bottom scrolls : to avoid ArrayOutOfBoundsException, I implemented tests on x and y.

I splitted the TILE_SIZE in two parts in order to fit the image proportions.

As I mentioned in the link in my previous comment, coupling the tiles with an array of WeakReference regulates memory usage : I replaced the boolean[][] loaded by WeakReference[][] and implemented the tileGet(x,y) function to get the tile.

The setImage() methods initializes the class fields such as the size of tiles.

The this._image field is inherited from a superclass and is implemented as below :

protected BufferedImage _image = null;

I hope this could help someone.