Knowledge Base

How To Create a Dynamically Scrolling Graph

Article ID: 183333

Article Last Modified on 6/29/2004

APPLIES TO

Microsoft Visual Basic 5.0 Learning Edition
Microsoft Visual Basic 6.0 Learning Edition
Microsoft Visual Basic 5.0 Professional Edition
Microsoft Visual Basic 6.0 Professional Edition
Microsoft Visual Basic 5.0 Enterprise Edition
Microsoft Visual Basic 6.0 Enterprise Edition

This article was previously published under Q183333

SUMMARY

This article shows you how to create a dynamically scrolling graph in Visual Basic. You can use the information in this article to create a graph as data is generated, such as in a monitoring program.

MORE INFORMATION

The sample project uses Timer and PictureBox controls. The graph is first created in memory and then copied to the PictureBox control using the BitBlt function. This method is used to allow the PictureBox control to update properly when another window partially or completely covers the PictureBox control.

The next section shows you how to create the sample project.

To Create the Sample Project

Start a new Standard EXE project in Visual Basic. Form1 is created by default.
Add a Timer and a PictureBox control to Form1.

Copy the following code to the Code window of Form1:

      Option Explicit
      Private Const SRCCOPY = &HCC0020 ' (DWORD) dest = source
      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

      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

From the Run menu, click Start or press the F5 key to start the program. A sine wave in red is displayed in the PictureBox control.

Additional query words: kbVBp kbdsd kbDSupport kbVBp600 kbSDKWin32 kbAPI kbVBp500

Keywords: kbhowto KB183333

Microsoft KB Archive/183333

Contents

How To Create a Dynamically Scrolling Graph

SUMMARY

MORE INFORMATION

To Create the Sample Project