Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!lll-winken!uunet!tektronix!tekgen!jonh
From: jonh@tekgen.BV.TEK.COM (Jon Howell)
Newsgroups: comp.graphics
Subject: Re: Looking for simple fill algorithm
Message-ID: <4344@tekgen.BV.TEK.COM>
Date: 23 Apr 89 22:40:17 GMT
References: <390030@hpfcdq.HP.COM> <1718@blake.acs.washington.edu>
Reply-To: jonh@tekgen.BV.TEK.COM (Jon Howell)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 45

The basics are covered in Foley  and Van Dam's _Fundamentals_of_Interactive_
_Computer_Graphics_, pp. 448-449 in pseudocode:
A FLOOD FILL converts all adjecent values of the same color to another
color.  A BOUNDARY FILL converts all pixels within a certain-colored boundary
to another color.
Foley & Van Dam's FLOOD FILL code:
procedure FLOOD_FILL_4(
	x, y,			{Starting point}
	old_value,		{value to convert}
	new_value: integer);	{Color to conver to}
begin
	if READ_PIXEL(x,y)=old_value
		then begin
			WRITE_PIXEL(x,y,new_value); {change color}
			{Attempt to propagate in four (eight) directions}
			FLOOD_FILL_4(x,y-1, old_value, new_value);
			{Repeat for (x,y+1..),(x-1,y..),(x+1,y..), and
			four more if you want an 8-bounded (diag.) region}
		end
end

procedure BOUNDARY_FILL_4(
	x, y,			{Starting point}
	boundary_value,		{boundary color}
	new_value: integer);	{Color to fill with}
	{it is permissible to have new_value=boundary_value; otherwise no
	  pixels may be initially set to new_value} [huh?!?]
	begin
		if READ_PIXEL(x,y)<>boundary_value	{boundary not reached}
		and READ_PIXEL(x,y)<>new_value	{and prev. filled pel not "  }
			then begin
				WRITE_PIXEL(x, y, new_value);	{change color}
				{four (eight) call to BOUNDARY FILL}
			end
end

Get the book.  Lots of handy code and algoritms amid the explanations of
hardware.  Hope you can make sense of the PASCAL pseudocode.  He shoulda
used C. :-)
		--Jon
-- 
jonh@tekgen.bv.tek.com     (503) MAK-SEMA  Jon Howell | Q: How come they never
  //  //  //  _  __    _   .  .   . .    ___   .  _   | play that on the radio?
 //  //  //  / \(_ __ (_)  |\/|  /| |\ |  |   /| /    | A: They should.
//  //  //   \_/__)    /   |  | /"| | \| _|_ /"| \_   |             --Dave Barry