Public Class Form1

    Dim bmp As Bitmap
    Dim lastMouseX, lastMouseY As Integer


    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        bmp = New Bitmap(PictureBox1.Width, PictureBox1.Width, Imaging.PixelFormat.Format32bppArgb)
    End Sub



    Private Sub btnGo_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGo.Click

        'recreate the bitmap
        bmp = Nothing
        bmp = New Bitmap(PictureBox1.Width, PictureBox1.Width, Imaging.PixelFormat.Format32bppArgb)

        Dim g As Graphics = Graphics.FromImage(bmp)

        g.Clear(Color.Black)

        On Error Resume Next

        Dim X As Decimal, Y As Decimal
        Dim xsquare, ysquare As Decimal
        Dim dx As Decimal, dy As Decimal
        Dim i As Integer, j As Decimal, bail As Decimal
        Dim iter, mul, col As Integer
        Dim rangex1, rangex2, rangey1, rangey2 As Decimal
        Dim q(0 To bmp.Width + 1) As Decimal, p As Decimal

        Dim xpos, ypos As Integer
        Dim palette(256) As Color

        'set up a palette
        For i = 0 To 63
            palette(i) = Color.FromArgb(0, i * 4, (63 - i) * 4)
        Next
        For i = 64 To 127
            palette(i) = Color.FromArgb((i - 64) * 4, (127 - i) * 4, 0)
        Next
        For i = 128 To 191
            palette(i) = Color.FromArgb(255, 0, (i - 128) * 4)
        Next
        For i = 192 To 255
            palette(i) = Color.FromArgb((255 - i) * 4, 0, 255)
        Next

        rangex1 = txtRangex1.Text
        rangex2 = txtRangex2.Text
        rangey1 = txtRangey1.Text
        rangey2 = txtRangey2.Text

        iter = Int(txtIterations.Text)
        mul = 255 / iter
        bail = txtBailout.Text
        dx = (rangex2 - rangex1) / bmp.Width
        dy = (rangey2 - rangey1) / bmp.Height

        q(0) = rangey2
        For i = 1 To bmp.Width
            q(i) = q(i - 1) - dy
        Next i

        ProgressBar1.Maximum = bmp.Width
        xpos = 0 : ypos = 0

        For p = rangex1 To rangex2 Step dx
            i = 0

            For j = rangey1 To rangey2 Step dy
                X = 0 : Y = 0 : xsquare = 0 : ysquare = 0 : col = 1

                Do
                    If col > iter Then
                        bmp.SetPixel(xpos, ypos, Color.Black)
                        Exit Do
                    End If
                    If Math.Sqrt(xsquare + ysquare) > bail Then
                        bmp.SetPixel(xpos, ypos, palette((col * mul) Mod 255))
                        Exit Do
                    End If
                    xsquare = X * X
                    ysquare = Y * Y
                    Y = Y * X
                    Y = Y + (Y + q(i))
                    X = xsquare - ysquare + p
                    col = col + 1
                Loop
                i = i + 1

                ypos = ypos + 1
                If ypos >= bmp.Height Then Exit For

            Next j

            xpos = xpos + 1
            If xpos >= bmp.Width Then Exit For
            ypos = 0
            ProgressBar1.Value = xpos
        Next p

        PictureBox1.Image = bmp
        ProgressBar1.Value = 0

    End Sub

    Private Sub PictureBox1_MouseMove(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseMove
        lastMouseX = e.X
        lastMouseY = e.Y
    End Sub

    Private Sub Zoom(ByVal amount As Decimal)
        Dim rangex1, rangex2, rangey1, rangey2 As Decimal
        Dim posx, posy As Decimal
        posx = lastMouseX
        posy = bmp.Height - lastMouseY

        rangex1 = txtRangex1.Text
        rangex2 = txtRangex2.Text
        rangey1 = txtRangey1.Text
        rangey2 = txtRangey2.Text

        posx = posx * (rangex2 - rangex1) / bmp.Width
        posx = posx + rangex1
        posy = posy * (rangey2 - rangey1) / bmp.Height
        posy = posy + rangey1

        txtRangex1.Text = posx - (rangex2 - rangex1) * amount
        txtRangex2.Text = posx + (rangex2 - rangex1) * amount
        txtRangey1.Text = posy - (rangey2 - rangey1) * amount
        txtRangey2.Text = posy + (rangey2 - rangey1) * amount

        btnGo_Click(Nothing, Nothing)
    End Sub


    Private Sub PictureBox1_DoubleClick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles PictureBox1.DoubleClick
        Zoom(0.25)
    End Sub

    Private Sub ZoomOutToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ZoomOutToolStripMenuItem.Click
        Zoom(1.25)
    End Sub

End Class