Flood Fill - Close but not working

[HellfireXP]

I'm working on a flood fill routine; I think I'm close, but it's not quite working right. I tested it with a bitmap 32x32 pixels with the starting point at 16,16. It just makes a cross, so it isn't extending across the entire bitmap. I have wracked my head over this code a few hours now, tweaking this and that with no success... Perhaps some smarter minds could take a look.

A few things to clarify:
Point is just a class containing integers X and Y.
#include <stack> is needed to access stack<>
Allegro 5 is the graphics library I'm using for colors and pixel manipulation.

void FloodFill(Point s, ALLEGRO_COLOR newClr)
{
	ALLEGRO_COLOR oldClr = al_get_pixel(aBMP,s.X,s.Y);
	if (oldClr.r == newClr.r &&
			oldClr.g == newClr.g &&
			oldClr.b == newClr.b &&
			oldClr.a == newClr.a) { return; }

	stack<Point> ptsCollection;
	ptsCollection.push(s);

	al_draw_pixel(s.X,s.Y,newClr);

	while (!ptsCollection.empty())
	{
		Point nPt = ptsCollection.top();
		ptsCollection.pop();

		if (nPt.X > 0) ProcessPoint(ptsCollection, nPt.X-1, nPt.Y, oldClr, newClr);
		if (nPt.Y > 0) ProcessPoint(ptsCollection, nPt.X, nPt.Y-1, oldClr, newClr);
		if (nPt.X < al_get_bitmap_width(aBMP)-1) ProcessPoint(ptsCollection, nPt.X+1, nPt.Y, oldClr, newClr);
		if (nPt.Y < al_get_bitmap_height(aBMP)-1) ProcessPoint(ptsCollection, nPt.X,nPt.Y+1, oldClr, newClr);
	}
}

void ProcessPoint(stack<Point> pts, int X, int Y, ALLEGRO_COLOR oClr, ALLEGRO_COLOR nClr)
{
	ALLEGRO_COLOR tempClr = al_get_pixel(aBMP,X,Y);
	if (tempClr.r == oClr.r &&
			tempClr.g == oClr.g &&
			tempClr.b == oClr.b &&
			tempClr.a == oClr.a)
	{
		pts.push(Point(X,Y));
		al_draw_pixel(X,Y,nClr);
	}
}

[helios]

You're passing the stack to ProcessPoint() by copy not by reference, so modifications made to it in ProcessPoint() are not reflected in the caller.

[HellfireXP]

doh! thanks, that should fix it.