Midpoint Circle Algorithm

midpoint.vb

Function MakeCircleApprox(cx As Integer, cy As Integer, radius As Integer) As List(Of Tuple(Of Integer, Integer))
            Dim ret_coords As New List(Of Tuple(Of Integer, Integer))
            Dim x, y, decisionOver2 As Integer
            x = radius
            y = 0
            decisionOver2 = 1 - x ' Decision criterion divided by 2 evaluated at x=r, y=0

            While (x >= y)
                ret_coords.Add(Tuple.Create(x + cx, y + cy))
                ret_coords.Add(Tuple.Create(y + cx, x + cy))
                ret_coords.Add(Tuple.Create(-x + cx, y + cy))
                ret_coords.Add(Tuple.Create(-y + cx, x + cy))
                ret_coords.Add(Tuple.Create(-x + cx, -y + cy))
                ret_coords.Add(Tuple.Create(-y + cx, -x + cy))
                ret_coords.Add(Tuple.Create(x + cx, -y + cy))
                ret_coords.Add(Tuple.Create(y + cx, -x + cy))
                y += 1

                If (decisionOver2 <= 0) Then
                    decisionOver2 += 2 * y + 1 'Change in decision criterion for y -> y+1
                Else
                    x -= 1
                    decisionOver2 += 2 * (y - x) + 1   ' Change for y -> y+1, x -> x-1
                End If
            End While

            Return ret_coords

        End Function