DOCUMENT:Q183333 11-JAN-2001 [vbwin] TITLE :HOWTO: Create a Dynamically Scrolling Graph PRODUCT :Microsoft Visual Basic for Windows PROD/VER: OPER/SYS: KEYWORDS:kbGrpDSVB ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 - Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 - Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 ------------------------------------------------------------------------------- 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 ---------------------------- 1. Start a new Standard EXE project in Visual Basic. Form1 is created by default. 2. Add a Timer and a PictureBox control to Form1. 3. 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 4. 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. (c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Arsenio Locsin, Microsoft Corporation Additional query words: kbVBp kbdsd kbDSupport kbVBp600 kbSDKWin32 kbAPI kbVBp500 ====================================================================== Keywords : kbGrpDSVB Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600 Issue type : kbhowto ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.