ID Number: Q80670
1.00
WINDOWS
Summary:
Using the Windows API call BitBlt, you can capture the entire
Microsoft Windows screen and place the image into a Visual Basic
picture box. You first get the handle to the desktop, then use the
desktop window handle to get the handle to the desktop's device
context (hDC), and finally use the Windows API call BitBlt to copy the
screen into the Picture property of a Visual Basic picture box
control.
This information applies to Microsoft Visual Basic programming system
version 1.0 for Windows.
More Information:
Example
-------
1. Start Visual Basic (VB.EXE). Form1 is created by default.
2. Create a picture box (Picture1) on Form1.
3. Set the following properties:
Control Property Value
------- -------- -----
Picture1 AutoRedraw True
Picture1 Visible False
4. Add the following code:
Global.Bas
----------
Type lrect
left As Integer
top As Integer
right As Integer
bottom As Integer
End Type
Declare Function GetDesktopWindow Lib "user" () As Integer
Declare Function GetDC Lib "user" (ByVal hWnd%) As Integer
'Note: The following Declare should be on one line:
Declare Function BitBlt Lib "GDI" (ByVal hDestDC%,
ByVal X%,
ByVal Y%,
ByVal nWidth%,
ByVal nHeight%,
ByVal hSrcDC%,
ByVal XSrc%,
ByVal YSrc%,
ByVal dwRop&
) As Integer
'Note: The following Declare should be on one line:
Declare Function ReleaseDC Lib "User"(ByVal hWnd As Integer,
ByVal hDC As Integer
) As Integer
Declare Sub GetWindowRect Lib "User" (ByVal hWnd%, lpRect As lrect)
Global Const True = -1
Global Const False = 0
Global TwipsPerPixel As Single
Form1
-----
Sub Form_Click ()
Call GrabScreen
End Sub
Sub GrabScreen ()
Dim winSize As lrect
' Assign information of the source bitmap
' Note that BitBlt requires coordinates in pixels
hwndSrc% = GetDesktopWindow()
hSrcDC% = GetDC(hwndSrc%)
XSrc% = 0: YSrc% = 0
Call GetWindowRect(hwndSrc%, winSize)
nWidth% = winSize.right 'Units in pixels
nHeight% = winSize.bottom 'Units in pixels
' Assign informate of the destination bitmap
hDestDC% = Form1.Picture1.hDC
x% = 0: Y% = 0
' Set global variable TwipsPerPixel and use to set
' picture box to same size as screen being grabbed.
' If picture box not the same size as picture being
' BitBlt'ed to it, it will chop off all that does not
' fit in the picture box.
GetTwipsPerPixel
Form1.Picture1.Top = 0
Form1.Picture1.Left = 0
Form1.Picture1.Width = (nWidth% + 1) * TwipsPerPixel
Form1.Picture1.Height = (nHeight% + 1) * TwipsPerPixel
' Assign the value of the constant SRCOPYY to the Raster operation.
dwRop& = &HCC0020
' Note function call must be on one line:
Suc% = BitBlt(hDestDC%, x%, Y%, nWidth%, nHeight%,
hSrcDC%, XSrc%, YSrc%, dwRop&)
' Release the DeskTopWindow's hDC to Windows.
' Windows may hang if this is not done.
Dmy% = ReleaseDC(hwndSrc%, hSrcDC%)
'Make the picture box visible.
Form1.Picture1.Visible = True
End Sub
Sub GetTwipsPerPixel ()
'Set a global variable with the Twips to Pixel ratio.
Form1.ScaleMode = 3
NumPix = Form1.ScaleHeight
Form1.ScaleMode = 1
TwipsPerPixel = Form1.ScaleHeight / NumPix
End Sub
5. Run the program and click on the form.
6. With the mouse, change the size of the form to see more of the
picture box. With a little work, you can use this as a "screen
saver" program.
Additional reference words: 1.00