Imports System.Drawing.Drawing2D

Partial Class Captcha
    Inherits System.Web.UI.Page

	Private Const CAPTCHA_WIDTH As Single = 180
	Private Const CAPTCHA_HEIGHT As Single = 80
	Private Const CAPTCHA_MSGLENGTH As Integer = 6

	Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
		Dim imgwidth As Integer = CType(CAPTCHA_WIDTH, Integer)
		Dim imgheight As Integer = CType(CAPTCHA_HEIGHT, Integer)

		Dim bmp As Bitmap
		bmp = New Bitmap(imgwidth, imgheight)

		Dim gfx As Graphics
		gfx = Graphics.FromImage(bmp)

		' Gradient will clear picture!
		' gfx.Clear(Color.Blue)

		Dim background As LinearGradientBrush
		background = New LinearGradientBrush(New Point(0, 0), New Point(imgwidth, 0), Color.Blue, Color.Black)
		background.WrapMode = WrapMode.TileFlipX

		Dim linecolour As Pen

		' define colours
		Dim bgblend As New ColorBlend
		Dim bgsrccolours() As Color = {Color.Black, Color.Blue, Color.DarkGreen, Color.DarkMagenta, Color.DarkOrchid}
		Dim bgsrclinecolours() As Color = {Color.Green, Color.Blue, Color.Brown, Color.DarkMagenta}
		bgblend.Colors = New Color() {bgsrccolours(Int(Rnd() * (UBound(bgsrclinecolours) + 1))), bgsrccolours(Int(Rnd() * (UBound(bgsrclinecolours) + 1))), bgsrccolours(Int(Rnd() * (UBound(bgsrclinecolours) + 1)))}
		linecolour = New Pen(bgsrclinecolours(Int(Rnd() * (UBound(bgsrclinecolours) + 1))))

		bgblend.Positions = New Single() {0.0, 0.5, 1.0}
		background.InterpolationColors = bgblend

		' draw the background
		gfx.FillRectangle(background, 0, 0, imgwidth, imgheight)

		' draw some gfx to mess up the display
		' objGraphics.DrawLine(new Pen(Color.Red), 0, 0, 200, 200)
		Dim loopi As Integer

		For loopi = 0 To 12
			gfx.DrawLine(linecolour, 0, CAPTCHA_HEIGHT * Rnd(), CAPTCHA_WIDTH, CAPTCHA_HEIGHT * Rnd())
			gfx.DrawLine(linecolour, CAPTCHA_WIDTH * Rnd(), 0, CAPTCHA_WIDTH * Rnd(), CAPTCHA_HEIGHT)
		Next
		linecolour.Color = Color.White
		For loopi = 0 To 4
			gfx.DrawLine(linecolour, 0, CAPTCHA_HEIGHT * Rnd(), CAPTCHA_WIDTH, CAPTCHA_HEIGHT * Rnd())
			gfx.DrawLine(linecolour, CAPTCHA_WIDTH * Rnd(), 0, CAPTCHA_WIDTH * Rnd(), CAPTCHA_HEIGHT)
		Next

		gfx.TextRenderingHint = Drawing.Text.TextRenderingHint.AntiAlias

		' create our message
		Dim msgpt1 As String
		Dim msgpt2 As String

		msgpt1 = ""
		msgpt2 = ""
		For loopi = 1 To CAPTCHA_MSGLENGTH / 2
			msgpt1 = msgpt1 & Int(Rnd() * 10).ToString
			msgpt2 = msgpt2 & Int(Rnd() * 10).ToString
		Next

		' font for our text
		Dim fontname1 As String
		Dim fontname2 As String

		Dim fontnames() As String = {"Arial", "Courier", "Times new Roman", "Georgia", "Trebuchet MS", "Impact", "MS Sans Serif", "Roman", "Comic Sans MS"}
		fontname1 = fontnames(Int(Rnd() * (UBound(fontnames) + 1)))
		fontname2 = fontnames(Int(Rnd() * (UBound(fontnames) + 1)))

		Dim style1 As FontStyle
		Dim style2 As FontStyle
		Dim styles() As FontStyle = {FontStyle.Bold, FontStyle.Italic, FontStyle.Regular, FontStyle.Underline}
		style1 = styles(Int(Rnd() * (UBound(styles) + 1)))
		style2 = styles(Int(Rnd() * (UBound(styles) + 1)))

		Dim fntpt1 As Font
		fntpt1 = New Font(fontname1, 32, style1)
		Dim fntpt2 As Font
		fntpt2 = New Font(fontname2, 32, style2)

		' part 1
		' find a position for it
		Dim fntsize As SizeF
		fntsize = gfx.MeasureString(msgpt1, fntpt1)
		Dim fntwidth As Single = fntsize.Width
		Dim fntheight As Single = fntsize.Height
		fntsize = gfx.MeasureString(msgpt2, fntpt2)
		fntwidth += fntsize.Width
		fntheight += fntsize.Height


		Dim leftoffset As Single
		Dim topoffset As Single
		leftoffset = (CAPTCHA_WIDTH - fntwidth) / 2.0
		topoffset = ((CAPTCHA_HEIGHT - fntheight) / 2.0) + (Rnd() * 20) + 12		'  + 12 stops negative slopes going off the top of the screen

		' Bend it a bit!
		Dim rotation As Single
		rotation = ((Rnd() * 16) - 4)
		gfx.RotateTransform(rotation)
		' draw our message
		gfx.DrawString(msgpt1, fntpt1, Brushes.White, leftoffset, topoffset)


		' part 2
		leftoffset = ((CAPTCHA_WIDTH - fntwidth) / 2.0) + (CAPTCHA_WIDTH / 2 + (Rnd() * 20))
		topoffset = ((CAPTCHA_HEIGHT - fntheight) / 2.0) + (Rnd() * 20) + 12

		' transform it a bit!
		gfx.ResetTransform()
		' inverse the old rotation
		gfx.RotateTransform(12 - rotation)
		gfx.ScaleTransform((Rnd() * 0.15) + 0.75, (Rnd() * 0.15) + 0.75)
		' draw our message
		gfx.DrawString(msgpt2, fntpt2, Brushes.White, leftoffset, topoffset)


		' save our msg
		Session.Add("CAPTCHA_TEXT", msgpt1 & msgpt2)

		' set the content type
		Response.ContentType = "image/GIF"
		' output our image
		bmp.Save(Response.OutputStream, ImageFormat.Gif)
		' clear up
		fntpt1.Dispose()
		fntpt2.Dispose()
		gfx.Dispose()
		bmp.Dispose()
	End Sub
End Class