draw a wave in VB.net panel

[qfchen]

Hi,

I need to draw a'wave form' in a panel inVB.net, the wave form will be updated once every one second. the problem is the screen blinking whenever it is updated. how can I solve this problem? the paint event code as below.

Private Sub Panel1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Panel1.Paint
        Dim i As Integer
        Dim x, y, offset As Integer
 
        offset = lastCnt - 2
 
       e.Graphics.DrawCurve(PenRed, trigP, 1, drawSegments, 0)
 
        MyBase.OnPaint(e)
    End Sub
 

[qfchen]

Hi need help on this. the waveform is updated dot by dot, the previous dots will be draw again when new dot moves in. that cause the whole panel screen blinking whenever update happen. any way to avoid re-draw previous dots again in new update?

[CroCrew]

Hello qfchen,

Can you post all your code so that I/we can simulate what you’re trying to do? Then maybe we can come up with an answer for you.

CroCrew~

[qfchen]

Hi CroCrew
I have a database, which capture real signals from a device, my application, every one second, read the signal from the database, then display as waveform on a panel screen, what I pass to the paint() is point array "Dim trigP(2000) As PointF", each time only the last point is new point, but have to redraw all the point in the Array.to show the waveform, Any way to display only one point without touching the previous points? below is the code

Private Sub Timer1_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        Dim cnt, CntLast, svCurrent, x, y As Integer
        Dim t1 As DateTime = Now
        Dim t2 As DateTime = Now
        Dim ft1, ft2, timeStamp, tStamp As Double
        Dim strSvCurrent As String
        Dim during As New TimeSpan(0, 2, 30)
 
        Timer1.Enabled = False
 
        t1 -= during
        t2 += during
        ft1 = t1.ToOADate()
        ft2 = t2.ToOADate()
 
        cnt = EM_AWARE_20kVTableAdapter.FillByDT(DataSet_ESD.EM_AWARE_20kV, ft1, ft2)
        If cnt <> 0 Then
            tStamp = DataSet_ESD.EM_AWARE_20kV.Rows(0).Item(3).ToString
            strSvCurrent = DataSet_ESD.EM_AWARE_20kV.Rows(0).Item(10).ToString
 
            svCurrent = Round((Convert.ToInt16(strSvCurrent) / 20) + TrigBoxMidPoint / 2)
            If firstRun = True Then
                firstRun = False
                timeStamp = tStamp
 
                x = Round(lastCnt * trigIntervel)
                y = Panel1.Height - svCurrent
                xData(lastCnt) = x
                yData(lastCnt) = y
                trigP(lastCnt) = New Point(x, y)
                lastCnt += 1
            ElseIf lastCnt * trigIntervel <= Panel1.Width - 1 Then
               timeStamp = tStamp
                x = Round(lastCnt * trigIntervel)
                y = Panel1.Height - svCurrent
                xData(lastCnt) = x
                yData(lastCnt) = y
                trigP(lastCnt) = New Point(x, y)
                lastCnt += 1
                If lastCnt > 3 Then
                    drawSegments = lastCnt - 2
                    Panel1.Refresh()
                End If
             Else
                timeStamp = tStamp
                For Counter = 1 To lastCnt - 1
                    yData(Counter - 1) = yData(Counter)
                    trigP(Counter - 1) = New Point(xData(Counter), yData(Counter))
                    Next
                x = Round(lastCnt * trigIntervel)
                y = Panel1.Height - svCurrent
                xData(lastCnt - 1) = x
                yData(lastCnt - 1) = y
                trigP(lastCnt - 1) = New Point(x, y)
                drawSegments = lastCnt - 2
                Panel1.Refresh()
                End If
        End If
 
        Timer1.Enabled = True
    End Sub
 

[qfchen]

any idea how to resolve the blinking issue when draw waveform in paint event?