Public Class Form1
    Public Const Pi = 3.14159265358979
    Public Structure 位置データ
        Public X As Double
        Public Y As Double
        Public 角度 As Double
    End Structure
    Private 現在位置 As 位置データ   ' 現在位置
    Private 色 As Color               ' 表示色
    Private MaxAng As Double         ' 最大角度
    Private MaxDsp As Double
    Private Function 色設定(設定種類 As Integer, ID As Integer) As Color
        Select Case 設定種類
            Case 1 : 色設定 = 色設定1(ID)
            Case 2 : 色設定 = 色設定2(ID)
            Case Else : 色設定 = 色設定3(ID)
        End Select
    End Function
    Private Function 色設定1(ID As Integer) As Color     ' 色設定方法を以下の3種類用意する
        If ID > 60 Then
            色設定1 = Color.FromArgb(8 * (ID - 60), 8 * (ID - 60), 4 * (ID - 60) + 125)
        ElseIf ID > 30 Then
            色設定1 = Color.FromArgb(8 * (60 - ID), 0, 0)
        Else
            色設定1 = Color.FromArgb(0, 8 * (30 - ID), 8 * (30 - ID))
        End If
    End Function
    Private Function 色設定2(ID As Integer) As Color
        If ID > 60 Then
            色設定2 = Color.FromArgb(8 * (ID - 60), 4 * (ID - 60) + 125, 8 * (ID - 60))
        ElseIf ID > 30 Then
            色設定2 = Color.FromArgb(8 * (60 - ID), 4 * (ID - 60) + 125, 0)
        Else
            色設定2 = Color.FromArgb(8 * ID, 8 * (30 - ID), 8 * (30 - ID))
        End If
    End Function
    Private Function 色設定3(ID As Integer) As Color
        If ID > 60 Then
            色設定3 = Color.FromArgb(8 * (ID - 60), 4 * (ID - 60) + 125, 8 * (ID - 60))
        ElseIf ID > 30 Then
            色設定3 = Color.FromArgb(8 * (60 - ID), 4 * (ID - 60) + 125, 0)
        Else
            色設定3 = Color.FromArgb(8 * ID, 8 * (30 - ID), 0)
        End If
    End Function
    Private Sub 初期位置(X As Double, Y As Double, TH As Double)
        現在位置.X = X : 現在位置.Y = Y : 現在位置.角度 = TH
    End Sub
    Private Sub 方向変更(TH As Double)
        現在位置.角度 = 現在位置.角度 + TH
    End Sub
    Private Sub 進む(長さ As Double)
        Dim TH As Double, X As Single, Y As Double
        Dim X1 As Integer, Y1 As Integer, X2 As Integer, Y2 As Integer
        Dim g As Graphics = PictureBox1.CreateGraphics()
        Dim p As Pen = New Pen(色)
        With 現在位置
            TH = .角度 * Pi / 180
            X = .X + 長さ * Math.Cos(TH) : Y = .Y + 長さ * Math.Sin(TH)
            X1 = .X + 10 : Y1 = 200 - .Y : X2 = X + 10 : Y2 = 200 - Y
            g.DrawLine(New Pen(色), X1, Y1, X2, Y2)
            .X = X : .Y = Y
        End With
    End Sub
    Private Sub 拡張コッホ曲線(N As Integer, TH As Double, 長さ As Double) '　第1編で示したように
        Dim nn As Integer, R1 As Double, R2 As Double, L As Double
        If (N <= 0) Then                      '  角度で描画方法を変える
            進む(長さ)
        Else ' 方向・長さを固定
            nn = N - 1 : L = 長さ / 3
            If TH <= MaxAng Then
                R1 = L / (2 * Math.Cos(TH * Pi / 180)) : R2 = 0
            Else
                R1 = L : R2 = L * (1 - 2 * Math.Cos(TH * Pi / 180))
            End If
            拡張コッホ曲線(nn, TH, L) : 方向変更(TH)
            拡張コッホ曲線(nn, TH, R1) : 方向変更(-TH)
            If R2 > 0 Then 拡張コッホ曲線(nn, TH, R2)
            方向変更(-TH)
            拡張コッホ曲線(nn, TH, R1) : 方向変更(TH)
            拡張コッホ曲線(nn, TH, L)
        End If
    End Sub
    Private Sub 描画(設定種類 As Integer)
        Dim g As Graphics = PictureBox1.CreateGraphics()
        Dim i As Integer
        g.Clear(Color.Black)
        MaxAng = Val(TextBox1.Text) : MaxDsp = Val(TextBox2.Text)
        For i = MaxDsp To 0 Step -1
            初期位置(0, 0, 0) : 色 = 色設定(設定種類, i)
            拡張コッホ曲線(7, i, 300)
        Next
        初期位置(0, 0, 0) : 色 = Color.FromArgb(255, 255, 0)
        拡張コッホ曲線(7, 60, 300)
    End Sub
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        描画(1)
    End Sub
    Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
        描画(2)
    End Sub
    Private Sub Button3_Click(sender As System.Object, e As System.EventArgs) Handles Button3.Click
        描画(3)
    End Sub
End Class