The information in this article applies to:
- Standard, Professional, and Enterprise Editions of Microsoft Visual
Basic, 16-bit and 32-bit, for Windows, version 4.0
SUMMARY
This article shows how to capture any form or window including the screen
into a Visual Basic Picture object. Once the on-screen image is captured in
the Picture object, it can easily be printed using the PaintPicture method
of the Visual Basic Printer object.
MORE INFORMATION
The included example provides several useful routines for capturing images.
All of the routines have been written to work under both 16- and 32-bit
Windows platforms and they contain full palette support. The routines in
the example can:
- Capture the entire contents of a form
- Capture the client area of a form
- Capture the entire screen
- Capture the active window on the screen
- Capture any portion of any window given a handle to it
- Create a Picture object from a bitmap and a palette
- Print a Picture object as large as possible on the page
Visual Basic 4.0 introduced a new Picture object. The Picture object is
actually a standard OLE type and it is documented in the Control
Developer's Kit (CDK.)
The CDK includes the function OleCreatePictureIndirect which can be used to
construct new Picture objects from Visual Basic 4.0. The routine
CreateBitmapPicture in the example calls OleCreatePictureIndirect to build
a Picture object from a handle to a bitmap and a handle to a palette. If
the Picture includes a valid palette, Visual Basic will know to use it when
rendering the Picture to the screen or printer. The CreateBitmapPicture
routine is used by the CaptureWindow routine to construct Picture objects
containing a bitmap of a part or all of a window.
The CaptureWindow routine in the example captures any portion of a window
given a window handle. The routine includes several parameters for
describing the exact portion of the window to capture. Capture Window works
by copying the on-screen image of a window into a new bitmap. It also
checks to see if the screen has a palette and if so it makes a copy of it.
CaptureWindow then calls CreateBitmapPicture to construct a bitmap from the
newly created bitmap and palette.
The CaptureForm, CaptureClient, CaptureScreen, and CaptureActiveWindow
routines included in the example all use CaptureWindow to capture specific
windows. CaptureForm and CaptureClient both call Capture window and pass it
the hWnd property of a Form object. CaptureScreen simply gets the handle to
the desk top window and calls CaptureWindow. Similarly, CaptureActiveWindow
just gets the window handle of the active window and calls CaptureWindow.
Once the desired image is captured in a Picture object, it is easy to print
in Visual Basic 4.0 using the PaintPicture method of the Printer object.
The example provides the routine PrintPictureToFitPage that uses the
PaintPictureMethod to print the captured images as large as possible in the
printable area of the page.
Example
- Start a new project. Form1 is created by default.
- Place six CommandButtons on the form along the left side.
- Place one picture box on the form to the right of the buttons.
- Put the following code in Form1:
'--------------------------------------------------------------------
' Capture the entire screen
Private Sub Command1_Click()
Set Picture1.Picture = CaptureScreen()
End Sub
' Capture the entire form including title and border
Private Sub Command2_Click()
Set Picture1.Picture = CaptureForm(Me)
End Sub
' Capture the client area of the form
Private Sub Command3_Click()
Set Picture1.Picture = CaptureClient(Me)
End Sub
' Capture the active window after two seconds
Private Sub Command4_Click()
MsgBox "Two seconds after you close this dialog " & _
"the active window will be captured."
' Wait for two seconds
Dim EndTime As Date
EndTime = DateAdd("s", 2, Now)
Do Until Now > EndTime
DoEvents
Loop
Set Picture1.Picture = CaptureActiveWindow()
' Set focus back to form
Me.SetFocus
End Sub
' Print the current contents of the picture box
Private Sub Command5_Click()
PrintPictureToFitPage Printer, Picture1.Picture
Printer.EndDoc
End Sub
' Clear out the picture box
Private Sub Command6_Click()
Set Picture1.Picture = Nothing
End Sub
' Initialize the form and controls
Private Sub Form_Load()
Me.Caption = "Capture and Print Example"
Command1.Caption = "&Screen"
Command2.Caption = "&Form"
Command3.Caption = "&Client"
Command4.Caption = "&Active"
Command5.Caption = "&Print"
Command6.Caption = "C&lear"
Picture1.AutoSize = True
End Sub
'--------------------------------------------------------------------
- Add a new standard module to the project (module1 by default).
- Put the following code in the new module:
'--------------------------------------------------------------------
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
' Visual Basic 4.0 16/32 Capture Routines
'
' This module contains several routines for capturing windows into a
' picture. All the routines work on both 16 and 32 bit Windows
' platforms.
' The routines also have palette support.
'
' CreateBitmapPicture - Creates a picture object from a bitmap and
' palette
' CaptureWindow - Captures any window given a window handle
' CaptureActiveWindow - Captures the active window on the desktop
' CaptureForm - Captures the entire form
' CaptureClient - Captures the client area of a form
' CaptureScreen - Captures the entire screen
' PrintPictureToFitPage - prints any picture as big as possible on
' the page
'
' NOTES
' - No error trapping is included in these routines
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
Option Explicit
Option Base 0
Private Type PALETTEENTRY
peRed As Byte
peGreen As Byte
peBlue As Byte
peFlags As Byte
End Type
Private Type LOGPALETTE
palVersion As Integer
palNumEntries As Integer
palPalEntry(255) As PALETTEENTRY ' Enough for 256 colors
End Type
Private Type GUID
Data1 As Long
Data2 As Integer
Data3 As Integer
Data4(7) As Byte
End Type
#If Win32 Then
Private Const RASTERCAPS As Long = 38
Private Const RC_PALETTE As Long = &H100
Private Const SIZEPALETTE As Long = 104
Private Type RECT
Left As Long
Top As Long
Right As Long
Bottom As Long
End Type
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 GetDeviceCaps Lib "GDI32" ( _
ByVal hDC As Long, ByVal iCapabilitiy As Long) As Long
Private Declare Function GetSystemPaletteEntries Lib "GDI32" ( _
ByVal hDC As Long, ByVal wStartIndex As Long, _
ByVal wNumEntries As Long, lpPaletteEntries As PALETTEENTRY) _
As Long
Private Declare Function CreatePalette Lib "GDI32" ( _
lpLogPalette As LOGPALETTE) As Long
Private Declare Function SelectObject Lib "GDI32" ( _
ByVal hDC As Long, ByVal hObject As Long) As Long
Private Declare Function BitBlt Lib "GDI32" ( _
ByVal hDCDest As Long, ByVal XDest As Long, _
ByVal YDest As Long, ByVal nWidth As Long, _
ByVal nHeight As Long, ByVal hDCSrc As Long, _
ByVal XSrc As Long, ByVal YSrc As Long, ByVal dwRop As Long) _
As Long
Private Declare Function DeleteDC Lib "GDI32" ( _
ByVal hDC As Long) As Long
Private Declare Function GetForegroundWindow Lib "USER32" () _
As Long
Private Declare Function SelectPalette Lib "GDI32" ( _
ByVal hDC As Long, ByVal hPalette As Long, _
ByVal bForceBackground As Long) As Long
Private Declare Function RealizePalette Lib "GDI32" ( _
ByVal hDC As Long) As Long
Private Declare Function GetWindowDC Lib "USER32" ( _
ByVal hWnd As Long) As Long
Private Declare Function GetDC Lib "USER32" ( _
ByVal hWnd As Long) As Long
Private Declare Function GetWindowRect Lib "USER32" ( _
ByVal hWnd As Long, lpRect As RECT) As Long
Private Declare Function ReleaseDC Lib "USER32" ( _
ByVal hWnd As Long, ByVal hDC As Long) As Long
Private Declare Function GetDesktopWindow Lib "USER32" () As Long
Private Type PicBmp
Size As Long
Type As Long
hBmp As Long
hPal As Long
Reserved As Long
End Type
Private Declare Function OleCreatePictureIndirect _
Lib "olepro32.dll" ( PicDesc As PicBmp, RefIID As GUID, _
ByVal fPictureOwnsHandle As Long, IPic As IPicture) As Long
#ElseIf Win16 Then
Private Const RASTERCAPS As Integer = 38
Private Const RC_PALETTE As Integer = &H100
Private Const SIZEPALETTE As Integer = 104
Private Type RECT
Left As Integer
Top As Integer
Right As Integer
Bottom As Integer
End Type
Private Declare Function CreateCompatibleDC Lib "GDI" ( _
ByVal hDC As Integer) As Integer
Private Declare Function CreateCompatibleBitmap Lib "GDI" ( _
ByVal hDC As Integer, ByVal nWidth As Integer, _
ByVal nHeight As Integer) As Integer
Private Declare Function GetDeviceCaps Lib "GDI" ( _
ByVal hDC As Integer, ByVal iCapabilitiy As Integer) As Integer
Private Declare Function GetSystemPaletteEntries Lib "GDI" ( _
ByVal hDC As Integer, ByVal wStartIndex As Integer, _
ByVal wNumEntries As Integer, _
lpPaletteEntries As PALETTEENTRY) As Integer
Private Declare Function CreatePalette Lib "GDI" ( _
lpLogPalette As LOGPALETTE) As Integer
Private Declare Function SelectObject Lib "GDI" ( _
ByVal hDC As Integer, ByVal hObject As Integer) As Integer
Private Declare Function BitBlt Lib "GDI" ( _
ByVal hDCDest As Integer, ByVal XDest As Integer, _
ByVal YDest As Integer, ByVal nWidth As Integer, _
ByVal nHeight As Integer, ByVal hDCSrc As Integer, _
ByVal XSrc As Integer, ByVal YSrc As Integer, _
ByVal dwRop As Long) As Integer
Private Declare Function DeleteDC Lib "GDI" ( _
ByVal hDC As Integer) As Integer
Private Declare Function GetForegroundWindow Lib "USER" _
Alias "GetActiveWindow" () As Integer
Private Declare Function SelectPalette Lib "USER" ( _
ByVal hDC As Integer, ByVal hPalette As Integer, ByVal _
bForceBackground As Integer) As Integer
Private Declare Function RealizePalette Lib "USER" ( _
ByVal hDC As Integer) As Integer
Private Declare Function GetWindowDC Lib "USER" ( _
ByVal hWnd As Integer) As Integer
Private Declare Function GetDC Lib "USER" ( _
ByVal hWnd As Integer) As Integer
Private Declare Function GetWindowRect Lib "USER" ( _
ByVal hWnd As Integer, lpRect As RECT) As Integer
Private Declare Function ReleaseDC Lib "USER" ( _
ByVal hWnd As Integer, ByVal hDC As Integer) As Integer
Private Declare Function GetDesktopWindow Lib "USER" () As Integer
Private Type PicBmp
Size As Integer
Type As Integer
hBmp As Integer
hPal As Integer
Reserved As Integer
End Type
Private Declare Function OleCreatePictureIndirect _
Lib "oc25.dll" ( PictDesc As PicBmp, RefIID As GUID, _
ByVal fPictureOwnsHandle As Integer, IPic As IPicture) _
As Integer
#End If
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
' CreateBitmapPicture
' - Creates a bitmap type Picture object from a bitmap and palette
'
' hBmp
' - Handle to a bitmap
'
' hPal
' - Handle to a Palette
' - Can be null if the bitmap doesn't use a palette
'
' Returns
' - Returns a Picture object containing the bitmap
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
#If Win32 Then
Public Function CreateBitmapPicture(ByVal hBmp As Long, _
ByVal hPal As Long) As Picture
Dim r As Long
#ElseIf Win16 Then
Public Function CreateBitmapPicture(ByVal hBmp As Integer, _
ByVal hPal As Integer) As Picture
Dim r As Integer
#End If
Dim Pic As PicBmp
' IPicture requires a reference to "Standard OLE Types"
Dim IPic As IPicture
Dim IID_IDispatch As GUID
' Fill in with IDispatch Interface ID
With IID_IDispatch
.Data1 = &H20400
.Data4(0) = &HC0
.Data4(7) = &H46
End With
' Fill Pic with necessary parts
With Pic
.Size = Len(Pic) ' Length of structure
.Type = vbPicTypeBitmap ' Type of Picture (bitmap)
.hBmp = hBmp ' Handle to bitmap
.hPal = hPal ' Handle to palette (may be null)
End With
' Create Picture object
r = OleCreatePictureIndirect(Pic, IID_IDispatch, 1, IPic)
' Return the new Picture object
Set CreateBitmapPicture = IPic
End Function
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
' CaptureWindow
' - Captures any portion of a window
'
' hWndSrc
' - Handle to the window to be captured
'
' Client
' - If True CaptureWindow captures from the client area of the
' window
' - If False CaptureWindow captures from the entire window
'
' LeftSrc, TopSrc, WidthSrc, HeightSrc
' - Specify the portion of the window to capture
' - Dimensions need to be specified in pixels
'
' Returns
' - Returns a Picture object containing a bitmap of the specified
' portion of the window that was captured
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
''''''
'
#If Win32 Then
Public Function CaptureWindow(ByVal hWndSrc As Long, _
ByVal Client As Boolean, ByVal LeftSrc As Long, _
ByVal TopSrc As Long, ByVal WidthSrc As Long, _
ByVal HeightSrc As Long) As Picture
Dim hDCMemory As Long
Dim hBmp As Long
Dim hBmpPrev As Long
Dim r As Long
Dim hDCSrc As Long
Dim hPal As Long
Dim hPalPrev As Long
Dim RasterCapsScrn As Long
Dim HasPaletteScrn As Long
Dim PaletteSizeScrn As Long
#ElseIf Win16 Then
Public Function CaptureWindow(ByVal hWndSrc As Integer, _
ByVal Client As Boolean, ByVal LeftSrc As Integer, _
ByVal TopSrc As Integer, ByVal WidthSrc As Long, _
ByVal HeightSrc As Long) As Picture
Dim hDCMemory As Integer
Dim hBmp As Integer
Dim hBmpPrev As Integer
Dim r As Integer
Dim hDCSrc As Integer
Dim hPal As Integer
Dim hPalPrev As Integer
Dim RasterCapsScrn As Integer
Dim HasPaletteScrn As Integer
Dim PaletteSizeScrn As Integer
#End If
Dim LogPal As LOGPALETTE
' Depending on the value of Client get the proper device context
If Client Then
hDCSrc = GetDC(hWndSrc) ' Get device context for client area
Else
hDCSrc = GetWindowDC(hWndSrc) ' Get device context for entire
' window
End If
' Create a memory device context for the copy process
hDCMemory = CreateCompatibleDC(hDCSrc)
' Create a bitmap and place it in the memory DC
hBmp = CreateCompatibleBitmap(hDCSrc, WidthSrc, HeightSrc)
hBmpPrev = SelectObject(hDCMemory, hBmp)
' Get screen properties
RasterCapsScrn = GetDeviceCaps(hDCSrc, RASTERCAPS) ' Raster
'capabilities
HasPaletteScrn = RasterCapsScrn And RC_PALETTE ' Palette
'support
PaletteSizeScrn = GetDeviceCaps(hDCSrc, SIZEPALETTE) ' Size of
' palette
' If the screen has a palette make a copy and realize it
If HasPaletteScrn And (PaletteSizeScrn = 256) Then
' Create a copy of the system palette
LogPal.palVersion = &H300
LogPal.palNumEntries = 256
r = GetSystemPaletteEntries(hDCSrc, 0, 256, _
LogPal.palPalEntry(0))
hPal = CreatePalette(LogPal)
' Select the new palette into the memory DC and realize it
hPalPrev = SelectPalette(hDCMemory, hPal, 0)
r = RealizePalette(hDCMemory)
End If
' Copy the on-screen image into the memory DC
r = BitBlt(hDCMemory, 0, 0, WidthSrc, HeightSrc, hDCSrc, _
LeftSrc, TopSrc, vbSrcCopy)
' Remove the new copy of the on-screen image
hBmp = SelectObject(hDCMemory, hBmpPrev)
' If the screen has a palette get back the palette that was
' selected in previously
If HasPaletteScrn And (PaletteSizeScrn = 256) Then
hPal = SelectPalette(hDCMemory, hPalPrev, 0)
End If
' Release the device context resources back to the system
r = DeleteDC(hDCMemory)
r = ReleaseDC(hWndSrc, hDCSrc)
' Call CreateBitmapPicture to create a picture object from the
' bitmap and palette handles. Then return the resulting picture
' object.
Set CaptureWindow = CreateBitmapPicture(hBmp, hPal)
End Function
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
' CaptureScreen
' - Captures the entire screen
'
' Returns
' - Returns a Picture object containing a bitmap of the screen
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
Public Function CaptureScreen() As Picture
#If Win32 Then
Dim hWndScreen As Long
#ElseIf Win16 Then
Dim hWndScreen As Integer
#End If
' Get a handle to the desktop window
hWndScreen = GetDesktopWindow()
' Call CaptureWindow to capture the entire desktop give the handle
' and return the resulting Picture object
Set CaptureScreen = CaptureWindow(hWndScreen, False, 0, 0, _
Screen.Width \ Screen.TwipsPerPixelX, _
Screen.Height \ Screen.TwipsPerPixelY)
End Function
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
' CaptureForm
' - Captures an entire form including title bar and border
'
' frmSrc
' - The Form object to capture
'
' Returns
' - Returns a Picture object containing a bitmap of the entire
' form
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
Public Function CaptureForm(frmSrc As Form) As Picture
' Call CaptureWindow to capture the entire form given it's window
' handle and then return the resulting Picture object
Set CaptureForm = CaptureWindow(frmSrc.hWnd, False, 0, 0, _
frmSrc.ScaleX(frmSrc.Width, vbTwips, vbPixels), _
frmSrc.ScaleY(frmSrc.Height, vbTwips, vbPixels))
End Function
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
' CaptureClient
' - Captures the client area of a form
'
' frmSrc
' - The Form object to capture
'
' Returns
' - Returns a Picture object containing a bitmap of the form's
' client area
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
Public Function CaptureClient(frmSrc As Form) As Picture
' Call CaptureWindow to capture the client area of the form given
' it's window handle and return the resulting Picture object
Set CaptureClient = CaptureWindow(frmSrc.hWnd, True, 0, 0, _
frmSrc.ScaleX(frmSrc.ScaleWidth, frmSrc.ScaleMode, vbPixels), _
frmSrc.ScaleY(frmSrc.ScaleHeight, frmSrc.ScaleMode, vbPixels))
End Function
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
' CaptureActiveWindow
' - Captures the currently active window on the screen
'
' Returns
' - Returns a Picture object containing a bitmap of the active
' window
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
Public Function CaptureActiveWindow() As Picture
#If Win32 Then
Dim hWndActive As Long
Dim r As Long
#ElseIf Win16 Then
Dim hWndActive As Integer
Dim r As Integer
#End If
Dim RectActive As RECT
' Get a handle to the active/foreground window
hWndActive = GetForegroundWindow()
' Get the dimensions of the window
r = GetWindowRect(hWndActive, RectActive)
' Call CaptureWindow to capture the active window given it's
' handle and return the Resulting Picture object
Set CaptureActiveWindow = CaptureWindow(hWndActive, False, 0, 0, _
RectActive.Right - RectActive.Left, _
RectActive.Bottom - RectActive.Top)
End Function
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
' PrintPictureToFitPage
' - Prints a Picture object as big as possible
'
' Prn
' - Destination Printer object
'
' Pic
' - Source Picture object
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
Public Sub PrintPictureToFitPage(Prn As Printer, Pic As Picture)
Const vbHiMetric As Integer = 8
Dim PicRatio As Double
Dim PrnWidth As Double
Dim PrnHeight As Double
Dim PrnRatio As Double
Dim PrnPicWidth As Double
Dim PrnPicHeight As Double
' Determine if picture should be printed in landscape or portrait
' and set the orientation
If Pic.Height >= Pic.Width Then
Prn.Orientation = vbPRORPortrait ' Taller than wide
Else
Prn.Orientation = vbPRORLandscape ' Wider than tall
End If
' Calculate device independent Width to Height ratio for picture
PicRatio = Pic.Width / Pic.Height
' Calculate the dimentions of the printable area in HiMetric
PrnWidth = Prn.ScaleX(Prn.ScaleWidth, Prn.ScaleMode, vbHiMetric)
PrnHeight = Prn.ScaleY(Prn.ScaleHeight, Prn.ScaleMode, vbHiMetric)
' Calculate device independent Width to Height ratio for printer
PrnRatio = PrnWidth / PrnHeight
' Scale the output to the printable area
If PicRatio >= PrnRatio Then
' Scale picture to fit full width of printable area
PrnPicWidth = Prn.ScaleX(PrnWidth, vbHiMetric, Prn.ScaleMode)
PrnPicHeight = Prn.ScaleY(PrnWidth / PicRatio, vbHiMetric, _
Prn.ScaleMode)
Else
' Scale picture to fit full height of printable area
PrnPicHeight = Prn.ScaleY(PrnHeight, vbHiMetric, Prn.ScaleMode)
PrnPicWidth = Prn.ScaleX(PrnHeight * PicRatio, vbHiMetric, _
Prn.ScaleMode)
End If
' Print the picture using the PaintPicture method
Prn.PaintPicture Pic, 0, 0, PrnPicWidth, PrnPicHeight
End Sub
'--------------------------------------------------------------------
- Save the project.
- Run the project and test. You should be able to capture the form, the
form's client area, the screen, and the active window. You will also be
able to print any of these.
NOTES: Once you have captured the image you want in a Picture object you
can easily place it on the clipboard using the SetData method of the
Clipboard object.
|