Delphi - floodfill without canvas

Sometimes a region with a certain property has to be 
filled. Eg the brightness is above a threshold. The image
is assumed a field where the pixels are :

 MyField=array[0..width-1,0..height-1]of byte, integer;

The result is assumed also a field as above, the result 
pixel is set to 1 when it belongs to the area.

The property test is external and returns true when the
property meets the criteria :

 function test(x,y):boolean;

 eg : function test(x,y):boolean;
      begin
       result:=(Image.canvas.pixels[x,y] > threshold);
      end;

an additional function inside(x,y) has to be provided,
which checks a new pixel being inside the image.


procedure FloodFill(var image,FResult:MyField; startx,starty:integer);

procedure ff(a,b:integer);
begin
 if (FResult[a,b]=0)and(test(image[a,b])) then begin   // valid pixel
   FResult[a,b]:=1;	  // set the pixel as used
   if inside(a-1,b-1) then ff(a-1,b-1);
   if inside(a-1,b)   then ff(a-1,b);
   if inside(a-1,b+1) then ff(a-1,b+1);
   if inside(a,b-1)   then ff(a,b-1);
   if inside(a,b+1)   then ff(a,b+1);
   if inside(a+1,b-1) then ff(a+1,b-1);
   if inside(a+1,b)   then ff(a+1,b);
   if inside(a+1,b+1) then ff(a+1,b+1);
  end
 else FResult[a,b]:=-1;   // invalidate pixel
end;  // local proc ff


begin
 Fresult.clear;        // set the result field to zero
 ff(startx,starty);
end;

findings

• find regions which are greater/smaller than a certain number of pixels
• integrate over a region