Help with Flood Fill Algorithm
HellfireXP

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?

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1 2void FloodFill(Point s, ALLEGRO_COLOR newClr) 3{ 4 al_lock_bitmap(FOCUS,ALLEGRO_PIXEL_FORMAT_ANY,ALLEGRO_LOCK_READWRITE); 5 ALLEGRO_COLOR oldClr = al_get_pixel(FOCUS,s.X,s.Y); 6 if (oldClr.r == newClr.r && 7 oldClr.g == newClr.g && 8 oldClr.b == newClr.b && 9 oldClr.a == newClr.a) { return; } 10 11 stack<Point> ptsCollection; 12 ptsCollection.push(s); 13 14 al_draw_pixel(s.X,s.Y,newClr); 15 16 while (!ptsCollection.empty()) 17 { 18 Point nPt = ptsCollection.top(); 19 ptsCollection.pop(); 20 21 if (nPt.X > 0) ProcessPoint(ptsCollection, nPt.X-1, nPt.Y, oldClr, newClr); 22 if (nPt.Y > 0) ProcessPoint(ptsCollection, nPt.X, nPt.Y-1, oldClr, newClr); 23 if (nPt.X < al_get_bitmap_width(FOCUS)-1) ProcessPoint(ptsCollection, nPt.X+1, nPt.Y, oldClr, newClr); 24 if (nPt.Y < al_get_bitmap_height(FOCUS)-1) ProcessPoint(ptsCollection, nPt.X,nPt.Y+1, oldClr, newClr); 25 } 26 al_unlock_bitmap(FOCUS); 27} 28 29void ProcessPoint(stack<Point>& ptsCollection, int X, int Y, ALLEGRO_COLOR oClr, ALLEGRO_COLOR nClr) 30{ 31 ALLEGRO_COLOR tempClr = al_get_pixel(FOCUS,X,Y); 32 if (tempClr.r == oClr.r && 33 tempClr.g == oClr.g && 34 tempClr.b == oClr.b && 35 tempClr.a == oClr.a) 36 { 37 ptsCollection.push(Point(X,Y)); 38 cout << X << ", " << Y << "\n"; 39 al_draw_pixel(X,Y,nClr); 40 } 41}

Matthew Leverton

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?

Elias

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).

HellfireXP

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

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