This flood fill code is adapted from a Tetris clone called "Tetanus On Drugs" by Damian Yerrick. It's licensed under the GNU General Public License and comes with ABSOLUTELY NO WARRANTY.

 #define BOARD_WIDTH  10
 #define BOARD_HEIGHT 20

 typedef struct MAP
 {
   unsigned char b[BOARD_HEIGHT][BOARD_WIDTH];
 } MAP;

 static void flood_loop(MAP *map, int x, int y,
                        unsigned int dst_c, unsigned  int src_c)
 {
   int fillL, fillR, i;
   int in_line = 1;

   /* find left side, filling along the way */
   fillL = fillR = x;
   while( in_line )
   {
     map->b[y][fillL] = dst_c;
     fillL--;
     in_line = (fillL < 0) ? 0 : (map->b[y][fillL] == src_c);
   }
   fillL++;

   /* find right side, filling along the way */
   in_line = 1;
   while( in_line )
   {
     map->b[y][fillR] = c;
     fillR++;
     in_line = (fillR > 9) ? 0 : (map->b[y][fillR] == fillC);
   }
   fillR--;

   /* search top and bottom */
   for(i = fillL; i <= fillR; i++)
   {
     if( y > 0 && map->b[y - 1][i] == fillC )
flood_loop(map, i, y - 1, c, fillC); 
     if( y < BOARD_HEIGHT && map->b[y + 1][i] == fillC )
flood_loop(map, i, y + 1, c, fillC); 
   }
 }

 void flood_fill(MAP *map, int x, int y, unsigned int c)
 {
   flood_loop(map, x, y, c, map->b[y][x]);
   map->b[y][x] = c;  /* some buggy optimizers needed this line */
 }
This is the same algorithm modified for Java by Claudio Santana

 int checkPixel(int[] oldPix, int[] newPix)
 {
   return (newPix[0] == oldPix[0] &&
   newPix[1] == oldPix[1]	&&
   newPix[2] == oldPix[2]  &&
   newPix[3] == oldPix[3] ? 1:0);
 }

 void floodLoop(WritableRaster raster, int x, int y, int[] fill, int[] old)
 {
   int fillL, fillR,i;
   int in_line=1;
   int[] aux =	{255,255,255,255};

   // find left side, filling along the way
   fillL = fillR = x;
   while(in_line!=0)
   {
     int[] p = raster.getPixel(fillL,y,aux);
     raster.setPixel(fillL,y,fill);
     fillL--;
     in_line = (fillL < 0) ? 0 : checkPixel(raster.getPixel(fillL,y,aux),old);
   }
   fillL++;

   // find right side, filling along the way
   in_line = 1;
   while (in_line!=0)
   {
     raster.setPixel(fillR,y,fill);
     fillR++;
     in_line = (fillR > d.width-1) ? 0 : checkPixel(raster.getPixel(fillR,y,aux),old);
   }
   fillR--;

   // look up and down
   for( i=fillL; i<=fillR; i++ )
   {
     if ( y>0 && checkPixel(raster.getPixel(i,y-1,aux),old)!=0 )
       floodLoop(raster,i,y-1,fill,old);
     if ( y
 }

 // Initial method you must call
 void floodLoop(WritableRaster raster, int x, int y, int[] fill)
 {
   int[] aux = new int[] {255,255,255,255};

   // validation so we don't fall in an infinite loop trying to
   // paint in the same color
   if ( checkPixel(raster.getPixel(x,y,aux),fill)!=0 )
     return;

   floodLoop(raster,x,y,fill,raster.getPixel(x,y,aux) );
 }