Q66783: _floodfill() May Not Stop at the Correct Boundary Color

Article: Q66783
Product(s): See article
Version(s): 6.00 6.00a
Operating System(s): MS-DOS
Keyword(s): ENDUSER | S_QUICKC buglist6.00 buglist6.00a | mspl13_c
Last Modified: 14-JAN-1991

The _floodfill() function takes a parameter that specifies the color
of the boundary at which flood-filling should stop. In certain cases,
the filling will stop at an incorrect boundary.

A situation where _floodfill() may fill incorrectly is if a screen
consists of two horizontal lines of the same color with one line near
the top of the screen and the other near the bottom. The problem
occurs if _floodfill() is then called with a start position at the
middle of the screen between these lines and the filling color is the
same as the lines, while the boundary color specified is something
else.

Because the fill color is different from the boundary color, the
filling should cover the entire screen because there is no boundary to
stop it. However, in actuality the filling stops when it reaches the
horizontal lines. The sample program below demonstrates this problem.

Microsoft has confirmed this to be a problem in C versions 6.00 and
6.00a and in QuickC versions 2.00, 2.01, 2.50, and 2.51. We are
researching this problem and will post new information here as it
becomes available.

Sample Code
-----------

#include <graph.h>
#include <conio.h>

void main(void)
{
   _setvideomode( _ERESCOLOR );
   _setcolor( 5 );

   _moveto( 0, 100 );
   _lineto( 640, 100 );
   _moveto( 0, 300 );
   _lineto( 640, 300 );

   _floodfill( 320, 200, 7 );
   getch();
   _setvideomode( _DEFAULTMODE );
}

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