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Create a dynamically scrolling graph in Visual Basic. Creates a graph as data is generated in real-

Create a dynamically scrolling graph in Visual Basic. Creates a graph as data is generated in real-time, such as in a monitoring program.

API Declarations


Private Const PS_SOLID = 0

Private Declare Function CreateCompatibleDC Lib "gdi32" _
(ByVal hdc As Long) As Long

Private Declare Function CreateCompatibleBitmap Lib "gdi32" _
(ByVal hdc As Long, _
ByVal nWidth As Long, _
ByVal nHeight As Long) As Long

Private Declare Function SelectObject Lib "gdi32" _
(ByVal hdc As Long, _
ByVal hObject As Long) As Long

Private Declare Function CreatePen Lib "gdi32" _
(ByVal nPenStyle As Long, _
ByVal nWidth As Long, _
ByVal crColor As Long) As Long

Private Declare Function LineTo Lib "gdi32" _
(ByVal hdc As Long, _
ByVal x As Long, _
ByVal y As Long) As Long

Private Declare Function MoveToEx Lib "gdi32" _
(ByVal hdc As Long, _
ByVal x As Long, _
ByVal y As Long, _
ByVal lpPoint As Long) As Long

Private Declare Function BitBlt Lib "gdi32" _
(ByVal hDestDC As Long, _
ByVal x As Long, _
ByVal y As Long, _
ByVal nWidth As Long, _
ByVal nHeight As Long, _
ByVal hSrcDC As Long, _
ByVal xSrc As Long, _
ByVal ySrc As Long, _
ByVal dwRop As Long) As Long

Private Const pWidth = 250 ' Width of picture box in pixels.
Private Const pHeight = 150 ' Height of picture box in pixels.
Private Const pGrid = 25 ' Distance between grid lines.
Private Const tInterval = 100 ' Interval between timer samplings
' in milliseconds.
Private Const pHeightHalf = pHeight \ 2
Dim counter As Long ' Number of data points logged so far. Used to
' sync grid.
Dim oldY As Long ' Contains the previous y coordinate.
Dim hDCh As Long, hPenB As Long, hPenC As Long



Rate Create a dynamically scrolling graph in Visual Basic. Creates a graph as data is generated in real-

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(1(1 Vote))

2) Add a Timer and a PictureBox control to Form1. 
3) Copy the following code to the Code window of Form1: 

Private Sub Form_Load()
    Dim hBmp As Long
    Dim i As Integer
    Me.Show
    Picture1.ScaleMode = 3
    Picture1.Left = 0
    Picture1.Top = 0
    Form1.ScaleMode = 3
    Picture1.Height = 155
    Picture1.Width = 255
    counter = 0
    hDCh = CreateCompatibleDC(Picture1.hdc)
    hBmp = CreateCompatibleBitmap(Picture1.hdc, _
                                 pWidth, _
                                 pHeight)
    Call SelectObject(hDCh, hBmp)
    hPenB = CreatePen(PS_SOLID, 0, vbBlack)
    hPenC = CreatePen(PS_SOLID, 0, vbRed)
    Call SelectObject(hDCh, hPenB)

' Plot horizontal grid lines.
    For i = pGrid To pHeight - 1 Step pGrid
        Picture1.Line (0, i)-(pWidth, i)
    Next

' Plot vertical grid lines.
    For i = pGrid - (counter Mod pGrid) To _
                     pWidth - 1 Step pGrid
        Picture1.Line (i, 0)-(i, pHeight)
    Next

    Call BitBlt(hDCh, _
               0, _
               0, _
               pWidth, _
               pHeight, _
               Picture1.hdc, _
               0, _
               0, _
               SRCCOPY)
    Timer1.Interval = 100
    Timer1.Enabled = True
    oldY = pHeightHalf
End Sub

Private Sub Timer1_Timer()
    Dim i As Integer
    Call BitBlt(hDCh, _
                  0, _
                  0, _
                  pWidth - 1, _
                  pHeight, _
                  hDCh, _
                  1, _
                  0, _
                  SRCCOPY)

    If counter Mod pGrid = 0 Then
        Call MoveToEx(hDCh, pWidth - 2, 0, 0)
        Call LineTo(hDCh, pWidth - 2, pHeight)
    End If

    i = Sin(0.1 * counter) * _
         (pHeightHalf - 1) + _
         pHeightHalf

    Call SelectObject(hDCh, hPenC)
    Call MoveToEx(hDCh, pWidth - 3, oldY, 0)
    Call LineTo(hDCh, pWidth - 2, i)
    Call SelectObject(hDCh, hPenB)
    Call BitBlt(Picture1.hdc, _
                  0, _
                  0, _
                  pWidth, _
                  pHeight, _
                  hDCh, _
                  0, _
                  0, _
                  SRCCOPY)
    counter = counter + 1
    oldY = i
End Sub