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From: Michael S <already5chosen@yahoo.com>
Newsgroups: comp.lang.c
Subject: Re: filling area by color atack safety
Date: Sun, 17 Mar 2024 15:15:19 +0200
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On Sun, 17 Mar 2024 12:54:34 +0000
bart <bc@freeuk.com> wrote:

> On 17/03/2024 12:46, Michael S wrote:
> > On Sat, 16 Mar 2024 11:33:20 +0000
> > Malcolm McLean <malcolm.arthur.mclean@gmail.com> wrote:
> >  =20
> >> On 16/03/2024 04:11, fir wrote: =20
> >>> i was writing simple editor (something like paint but more custom
> >>> for my eventual needs) for big pixel (low resolution) drawing
> >>>
> >>> it showed in a minute i need a click for changing given drawed
> >>> area of of one color into another color (becouse if no someone
> >>> would need to do it=C2=A0 by hand pixel by pixel and the need to
> >>> change color of given element is very common)
> >>>
> >>> there is very simple method of doing it - i men i click in given
> >>> color pixel then replace it by my color and call the same function
> >>> on adjacent 4 pixels (only need check if it is in screen at all
> >>> and if the color to change is that initial color
> >>>
> >>> int RecolorizePixelAndAdjacentOnes(int x, int y, unsigned
> >>> old_color, unsigned new_color)
> >>> {
> >>>   =C2=A0 if(old_color =3D=3D new_color) return 0;
> >>>
> >>>   =C2=A0 if(XYIsInScreen( x,=C2=A0 y))
> >>>   =C2=A0 if(GetPixelUnsafe(x,y)=3D=3Dold_color)
> >>>   =C2=A0 {
> >>>   =C2=A0=C2=A0=C2=A0 SetPixelSafe(x,y,new_color);
> >>>   =C2=A0=C2=A0=C2=A0 RecolorizePixelAndAdjacentOnes(x+1, y,=C2=A0 old=
_color,
> >>> new_color); RecolorizePixelAndAdjacentOnes(x-1, y,=C2=A0 old_color,
> >>> new_color); RecolorizePixelAndAdjacentOnes(x, y-1,=C2=A0 old_color,
> >>> new_color); RecolorizePixelAndAdjacentOnes(x, y+1,=C2=A0 old_color,
> >>> new_color); return 1;
> >>>   =C2=A0 }
> >>>
> >>>   =C2=A0 return 0;
> >>> }
> >>>
> >>> it work but im not quite sure how to estimate the safety of this
> >>> - incidentally as i said i use this editor to low res graphics
> >>> like 200x200 pixels or less, and it is only a toll of private use,
> >>> yet i got no time to work on it more than 1-2-3 days i guess but
> >>> still
> >>>
> >>> is there maybe simple way to improve it?
> >>   > =20
> >> This is a cheap and cheerful fllod fill. And it's easy to get right
> >> and shouldn't afall over. =20
> >=20
> > Except I don't understand why it works it all.
> > Can't fill area have sub-areas that only connected through
> > diagonal? =20
>=20
> Suppose you have an image which is a chessboard. You want to fill one
> of the black squares so that it is red.
>=20
> If you allow connectivity through the diagonals (so two notionally=20
> square pixels that only meet at their corners would be connected),
> then all the black squares would turn red, not just one.
>=20

That's what I want.
Do fir wants something else?