Name: rlT66838 Date: 08/04/99


The wrong image was created from a MemoryImageSource
because the constructor for the MemoryImageSource seemed to
ignore the offset provided.

For the code sample:
usecolors is a ColorModel
database is a byte[] that is width*height*depth long
area = width*height

This piece of code produces an Image that uses the first

//Test case
import java.awt.* ;
import java.awt.image.* ;
import java.awt.Color ;
import java.awt.Graphics ;


public class ImageBug extends Frame implements ImageObserver, Runnable
{

  int height = 100 ;
  int width = 100 ;
  int levels = 3 ;
  IndexColorModel cm ;
  Image image ;
  Thread irun ;
  boolean first = true ;

  byte[] db = new byte[ height*width*levels] ;


  public boolean imageUpdate( Image i
                            , int flags
                            , int a
                            , int b
                            , int c
                            , int d )
  { return ( true ) ;
  }

  public void createColorModel()
  {
    byte red[] = new byte[256] ;
    byte green[] = new byte[256] ;
    byte blue[] = new byte[256] ;
 
    for ( int i=0 ; i<256 ; i++ )
    { red[i] = (byte)( i & 0xff ) ;
      //green[i] = (byte)( i & 0xff ) ;
      blue[i] = (byte)( i & 0xff ) ;
      //commented out green so I could get purple
    }

    cm = new IndexColorModel( 8, 256, red, green, blue ) ;
  }

  public void generateBuggyImage( int offset )
  { // Initialize the database, Three slices, different shades of grey
    int l = 0 ;
    if ( first )
    { for ( int k=0 ; k<levels ;k++ )
      { for ( int i=0 ; i<height ; i++ )
        { for ( int j=0 ; j<width ; j++ )
          { if( k== 0)
                 db[l] = (byte)( 70 & 0xff ) ;
              if (k==1)
                 db[l] = (byte)( 150 & 0xff ) ;
              if (k==2)
                 db[l] = ( byte)( 230 & 0xff ) ;
              l++ ;
      } } }
      first = false ;
     }
     
     System.out.println("db length="+db.length) ;
     System.out.println("offset= "+offset) ;
     // Here the image is created using the offset,
     image = createImage( new MemoryImageSource( width, height, (ColorModel)cm,
                                                db, offset, width )) ;
   }

   public void generateForcedImage( int offset )
   {
     int area = width*height ;
     byte[] tempdb = new byte[area] ;

     // using the offset grab just the slice of the db we want to display
     for ( int i=0 ; i<area ; i++ )
        tempdb[i] = db[i+offset] ;

     // Create the image with an offset of zero, image is ok
     image = createImage( new MemoryImageSource( width, height, (ColorModel)cm,
                                                 tempdb, 0, width )) ;
   }

   public void paint( Graphics g )
   {
      g.drawImage( image, 10, 10, this ) ;
   }

   public void run()
   {
     // The thread runs generating six images. The first three attempt to
     // traverse the three slices of the database in turn. The output is
     // as if the offset is always 0 in the MemoryImageSource.
     // The second three cut out only the part of the database we are trying
     // to display. The output is fine.
     try
     { System.out.println("These images are created using the offset");
       for ( int i=0 ; i<3 ; i++ )
       { generateBuggyImage( i*width*height ) ;
         repaint() ;
         Thread.currentThread().sleep( 5000 ) ;
         // five second delay between new images
       }
       System.out.println("These are forcing the db and using offset of zero");
       for ( int i=0 ;i<3 ;i++ )
       { generateForcedImage( i*width*height ) ;
         repaint() ;
         Thread.currentThread().sleep( 5000 ) ;
       }
     }
     catch ( InterruptedException e )
     {}
     System.exit(0) ;
   }
       
   public void showBug()
   { irun = new Thread( this ) ;
     irun.start() ;
   }


   public static void main( String args[] )
   {
     
      ImageBug ib = new ImageBug() ;
      ib.createColorModel() ;
      ib.setSize(100,100) ;
      ib.show() ;
      ib.showBug() ;
   }
}
(Review ID: 83512)
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