Help with Flood Fill Algorithm

no-reply@allegro.cc (HellfireXP) — Tue, 25 Dec 2012 00:07:39 +0000

I am trying to write a flood fill algorithm using Allegro 5.0.7. Logically, my code should be working, but for some reason I don't think the set_pixel is being applied. The only thing I can think is the Allegro functions aren't doing what I think they are doing. My IDE is Visual C++ 2010. Can anyone help?

#SelectExpand
  1
  2void FloodFill(Point s, ALLEGRO_COLOR newClr)
  3{
al_lock_bitmap(FOCUS,ALLEGRO_PIXEL_FORMAT_ANY,ALLEGRO_LOCK_READWRITE);
ALLEGRO_COLOR oldClr = al_get_pixel(FOCUS,s.X,s.Y);
if (oldClr.r == newClr.r &&
    oldClr.g == newClr.g &&
    oldClr.b == newClr.b &&
    oldClr.a == newClr.a) { return; }
 10
stack<Point> ptsCollection;
ptsCollection.push(s);
 13
al_draw_pixel(s.X,s.Y,newClr);
 15
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(FOCUS)-1) ProcessPoint(ptsCollection, nPt.X+1, nPt.Y, oldClr, newClr);
  if (nPt.Y < al_get_bitmap_height(FOCUS)-1) ProcessPoint(ptsCollection, nPt.X,nPt.Y+1, oldClr, newClr);
}
al_unlock_bitmap(FOCUS);
 27}
 28
 29void ProcessPoint(stack<Point>& ptsCollection, int X, int Y, ALLEGRO_COLOR oClr, ALLEGRO_COLOR nClr)
 30{
ALLEGRO_COLOR tempClr = al_get_pixel(FOCUS,X,Y);
if (tempClr.r == oClr.r &&
    tempClr.g == oClr.g &&
    tempClr.b == oClr.b &&
    tempClr.a == oClr.a)
{
  ptsCollection.push(Point(X,Y));
  cout << X << ", " << Y << "\n";
  al_draw_pixel(X,Y,nClr);
}
 41}

no-reply@allegro.cc (Matthew Leverton) — Tue, 25 Dec 2012 00:52:52 +0000

Assuming your algorithm is correct and you are seeing your cout lines...

Are you sure that you have called al_set_target_bitmap() on the appropriate bitmap?

Are you then drawing that bitmap to the back buffer?

no-reply@allegro.cc (Elias) — Tue, 25 Dec 2012 02:25:38 +0000

I'd also use al_put_pixel, al_draw_pixel isn't really supposed to do much on a locked bitmap I think (at least the other al_draw_* functions aren't).

no-reply@allegro.cc (HellfireXP) — Tue, 25 Dec 2012 04:05:23 +0000

Thanks guys. The solution that worked was changing al_draw_pixel to al_put_pixel. I had the cout << in there just to try and see where my error was - I didn't plan on leaving it.

One thing I noticed was that all the coordinates kept being added to the stack over and over; thus none of them were applying the color to the bitmap or they'd have been removed. Good to know for future application - I'll use al_put_pixel instead.

Thanks.:D