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  1. #1
    Join Date
    Feb 2009

    TV static noise animation-adding random generator


    First forum posting.

    I am a newbie (retired social worker) using Visual Basic 2010 Express edition and need some help with an animation for an eLearning lesson. The animation illustrates a type of white noise (like TV static) called dynamic visual noise. I've got much of the code worked out (with a lot of help) but I discovered that the speed of the animation, using this code is wrong and need some help to fix the code, get it working correctly.

    You can view a Flash demo of this noise animation at http://elearningprojects.com/WN5.swf

    More info here about the visual noise animation (even a Delphi source code and Windows demo): http://www.st-andrews.ac.uk/~www_sp/.../personal/jgq/

    The animation has a 640 X 640 canvas, with 8 X 8 white and black dots filling it using 80 across and 80 down, for a total of 6400 dots. Some of these (approximately 400) change every second (1000 Ms) from white to black or black to white. These 400 dots need to be selected randomly every second.

    The VB code I am using is missing the ability to randomly select the 400 dots per second which are the dots to be changed (white to black or black to white).

    Here is the current (commented) code that needs an addition of a random generator for the 400 dots every second that will be changed:

    Option Strict On
    Public Class Form1
    Private gDotSize As Integer = 8
    Private gCanvasSize As Integer = 640
    Private gDelay As Integer = 100 'ms
    Private gProceed As Boolean = False
    Private gImage As New System.Drawing.Bitmap(gCanvasSize, gCanvasSize)
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Me.SetClientSizeCore(gCanvasSize, gCanvasSize)
    Me.Text = "Click the form to start and stop"
    'Set double-buffering so that graphics may be invalidated without causing flickering.
    SetStyle(ControlStyles.AllPaintingInWmPaint Or ControlStyles.DoubleBuffer Or ControlStyles.ResizeRedraw Or ControlStyles.UserPaint, True)
    End Sub
    Private Sub Form1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Click
    If gProceed Then
    gProceed = False
    gProceed = True
    Dim vThread As New System.Threading.Thread(AddressOf GenerateStatic_Background)
    With vThread
    .IsBackground = True
    .Name = "Thread for generating static"
    End With
    vThread.Start(New Object) 'You could pass an object into the thread here if you wanted.
    End If
    End Sub
    Private Sub GenerateStatic_Background(ByVal Arg As System.Object)
    'The canvas is square, so how many rows and columns will there be?
    Dim vRows As Integer = Convert.ToInt32(gCanvasSize / gDotSize)
    Dim vCols As Integer = Convert.ToInt32(gCanvasSize / gDotSize)
    'How many dots will there be total?
    Dim vTotalDots As Integer = Convert.ToInt32(vRows * vCols)
    'Create blank image to draw on.
    Dim vImg As New System.Drawing.Bitmap(gCanvasSize, gCanvasSize)
    Using vGr As System.Drawing.Graphics = System.Drawing.Graphics.FromImage(vImg)
    'Instance random generator object and seed data.
    Dim vGen As New System.Security.Cryptography.RNGCryptoServiceProvider
    'Prepare an empty array of bytes which will be used to store random seed data.
    'These random bytes will be converted to a 32-bit integer. Int32's are 4 bytes
    'in length; therefore the array will be 4 bytes in size. Remember, when
    'dimensioning static arrays, we do not specify the "length" of the array like
    'in C++, but instead we specify the "upper bounds" a.k.a. the last index of
    'the array, which would be 3 (0-3).
    Dim vSeed(3) As Byte
    'Fill the empty array with a cryptographically strong sequence of random values.
    'Instance a Random object using the random bytes (converted to an integer) as a seed.
    Dim vRand As Random = New Random(BitConverter.ToInt32(vSeed, 0))
    'Variables for choosing the color.
    Dim vCurrentRand As Integer = 0 'Black is 0; white is 1
    Dim vCurrentColor As System.Drawing.Color = System.Drawing.Color.Black
    'Do until told to stop by the user.
    While gProceed
    'Wait the desired period.
    'We will start on the first row on the left, work right across the columns, then drop
    'down to the second next row (back to the left), and again work right across the
    'columns, and so on...
    Dim vCurrentDot As New System.Drawing.Rectangle(0, 0, gDotSize, gDotSize)
    Dim vCurrentRow As Integer = 0
    Dim vCurrentCol As Integer = 0
    'Iterate each dot... come up with a random black or white state, and draw it to the image.
    For i As Integer = 0 To vTotalDots - 1
    'Generate random black or white state for this dot.
    vCurrentRand = vRand.Next(0, 2) 'Either 0 or 1
    If vCurrentRand = 0 Then vCurrentColor = System.Drawing.Color.Black Else vCurrentColor = System.Drawing.Color.White
    'Draw this dot.
    vGr.FillRectangle(New System.Drawing.SolidBrush(vCurrentColor), vCurrentDot)
    'Increment the current dot for the next iteration.
    vCurrentCol += 1 : vCurrentDot.X += gDotSize
    If vCurrentCol = vCols Then
    vCurrentCol = 0 : vCurrentDot.X = 0
    vCurrentRow += 1 : vCurrentDot.Y += gDotSize
    End If
    'Update the UI.
    If Me.InvokeRequired Then
    Me.Invoke(New DrawUpdate_Delegate(AddressOf DrawUpdate), CType(vImg, System.Object))
    Catch ex As Exception
    'Error cuz you ended the program without allowing the thread to stop.
    'To prevent this error, you could set gProceed = False in the Form_Closing event so the thread can end naturally.
    'This Try block just prevents the error message.
    End Try
    DrawUpdate(CType(vImg, System.Object))
    End If
    End While
    End Using
    End Sub
    Private Delegate Sub DrawUpdate_Delegate(ByVal Arg As System.Object)
    Private Sub DrawUpdate(ByVal Arg As System.Object)
    gImage = DirectCast(Arg, System.Drawing.Bitmap)
    End Sub
    Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
    e.Graphics.DrawImageUnscaled(gImage, 0, 0)
    End Sub
    End Class
    I would appreciate any code suggestions to add the random generator (described above) and where to add it in the above code. It would also be a huge help if I can change the specific number of random dots so I can try values ranging from 390-400 dots per second to see which value best replicates the precise animation speed needed.

    Thanks very much for your help.

    Kind Regards,

    Last edited by saratogacoach; February 21st, 2011 at 07:23 PM.

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