Q183333: HOWTO: Create a Dynamically Scrolling Graph
Article: Q183333
Product(s): Microsoft Visual Basic for Windows
Version(s):
Operating System(s):
Keyword(s): kbGrpDSVB
Last Modified: 11-JAN-2001
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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
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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
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Keywords : kbGrpDSVB
Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600
Issue type : kbhowto
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