' version 04-11-2016
' compile with: fbc -s console

' the flood_fill needs to know the boundries of the window/screen
' without them the routine start to check outside the window
' this leads to crashes (out of stack)
' the Line routine has clipping it will not draw outside the window

Sub flood_fill(x As Integer, y As Integer, target As UInteger, fill_color As UInteger)

    Dim As Long x_max, y_max
    ScreenInfo x_max, y_max

    ' 0, 0 is top left corner
    If Point(x,y) <> target Then Exit Sub

    Dim As Long l = x, r = x

    While Point(l -1, y) = target AndAlso l -1 > -1
        l = l -1
    Wend

    While Point(r +1, y) = target AndAlso r +1 < x_max
        r = r +1
    Wend

    Line (l,y) - (r,y), fill_color

    For x = l To r
        If y +1 < y_max Then flood_fill(x, y +1, target, fill_color)
        If y -1 >    -1 Then flood_fill(x, y -1, target, fill_color)
    Next

End Sub

' ------=< MAIN >=------

Dim As ULong i, col, x, y

ScreenRes 400, 400, 32
Randomize Timer

For i As ULong = 1 To 5
    Circle(Rnd * 400 ,Rnd * 400), i * 40, Rnd * &hFFFFFF
Next

' hit a key to end or close window
Do
    x = Rnd * 400
    y = Rnd * 400
    col = Point(x, y)
    flood_fill(x, y, col, Rnd * &hFFFFFF )
    Sleep 2000
    If InKey <> "" OrElse InKey = Chr(255) + "k" Then End
Loop