Public Class Form1

    Private img As New Bitmap(500, 500) '500x500サイズのImage
    Private gf As Graphics
    Dim k As Double, B As Double, DT As Double, NSEP As Integer, DB As Double
    Dim check As Boolean = True
    Private Sub InitData()
        k = Val(TextBox1.Text)
        B = Val(TextBox2.Text)
        DB = Val(TextBox3.Text)
        check = CheckBox1.Checked
        NSEP = 800 : DT = 2 * Math.PI / NSEP
    End Sub

    Private Function RED(I As Integer) As Integer
        RED = (I Mod &H1000000) \ &H10000
    End Function
    Private Function GREEN(I As Integer) As Integer
        GREEN = (I Mod &H10000) \ &H100
    End Function
    Private Function BLUE(I As Integer) As Integer
        BLUE = I Mod &H100
    End Function
    Private Function intX(X As Double) As Integer
        If check Then
            intX = X * 100 + 0.5
        Else
            intX = 250 + X * 40 + 0.5
        End If
    End Function
    Private Function intY(Y As Double) As Integer
         intY = 250 - Y * 20 + 0.5
    End Function
    Private Sub drawPic(X As Double, Y As Double, i As Integer)
        Dim IX As Integer = intX(X), IY As Integer = intY(Y)
        If IX >= 0 And IX < img.Width And IY >= 0 And IY < img.Height Then
            img.SetPixel(intX(X), intY(Y), Color.FromArgb(RED(i), GREEN(i), BLUE(i)))
        End If
    End Sub
    Private Sub drawAttract()
        Cursor.Current = Cursors.WaitCursor
        gf = Graphics.FromImage(img) : gf.Clear(Color.Black) '描画クリア
        Dim T As Double = 0, X As Double = 0.2, Y As Double = 0.1
        Dim XN As Double, YN As Double, i As Integer, DX As Double, DY As Double
        Dim iflag As Boolean
        For j = 1 To 8000
            iflag = True
            For i = 1 To NSEP
                If Not check Then drawPic(X, Y, j * 127)
                DX = Y * DT : DY = (-k * Y - X * X * X + B * Math.Cos(T)) * DT
                XN = X + DX : YN = Y + DY
                If XN > 100 Or XN < -100 Or YN > 100 Or YN < -100 Then
                    iflag = False : Exit For
                End If
                T = T + DT : X = XN : Y = YN
            Next
            If iflag Then drawPic(X, Y, j * 127)
        Next
        PictureBox1.Image = img : gf.Dispose()
        Cursor.Current = Cursors.Default

    End Sub
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        InitData()
        Timer1.Enabled = True
    End Sub

    Private Sub Timer1_Tick(sender As System.Object, e As System.EventArgs) Handles Timer1.Tick
        If B > 12.07 Then
            Timer1.Enabled = False
        Else
            Label1.Text = Format(B, "B = #0.00")
            drawAttract()
            B = B + DB
        End If
    End Sub
    Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
        Timer1.Enabled = False
    End Sub
    Private Sub Button3_Click(sender As System.Object, e As System.EventArgs) Handles Button3.Click
        InitData()
        drawAttract()
    End Sub
End Class