let rec cleanblack surface x y =
        Sdlvideo.put_pixel_color surface x y (255,255,255);
        if (x > 0) then
                begin
                if (Sdlvideo.get_pixel_color surface (x-1) y = (0,0,0)) then
                 cleanblack surface (x-1) y
                end;
        if (x < (w-1)) then
                begin
                if (Sdlvideo.get_pixel_color surface (x+1) y = (0,0,0)) then
                cleanblack surface (x+1) y
                end;
        if (y > 0) then
                begin
                if (Sdlvideo.get_pixel_color surface x (y-1) = (0,0,0)) then
                cleanblack surface x (y-1)
                end;
        if (y < (h-1)) then
                begin
                if (Sdlvideo.get_pixel_color surface x (y+1) = (0,0,0)) then
                cleanblack surface x (y+1)
                end