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Use of Window handle and BMP's

Posted on 2000-12-13
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Last Modified: 2008-03-10
I have used API functions to manipulate windows using their handles, eg setting top most etc.

I am interfacing with a video capture card and I have got a function from a direct video capture software library which it says "retrieves  the contents of a video window as a windows BMP image" and returns the handle to the a newly created windows BMP.

My question is what can I do with the handle? I want to transfer the image to a picturebox.
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Question by:nickwoolley
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15 Comments
 
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Accepted Solution

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l99057j earned 300 total points
ID: 15053
Private Declare Function CreateCompatibleBitmap Lib "gdi32" (ByVal hdc As Long, ByVal nWidth As Long, ByVal nHeight 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 Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hdc As Long) As Long
Private Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long
Public Declare Function DeleteDC Lib "gdi32" Alias "DeleteDC" (ByVal hdc As Long) As Long

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

Dim hNewDC As Long
Dim hOldBitmap As Long

'Create a device context
hNewDC = CreateCompatibleDC(Picture1.hdc)

'Select the bitmap into the device context...
hOldBitmap = SelectObject(hNewDC, hBMPHandle)
   
'Draw the picture into the picture box...
BitBlt Picture1.hdc, 0, 0, 20, 20, hNewDC, 0, 0, SRCCOPY
   
'Deselect the bitmap
SelectObject hNewDC, hOldBitmap
   
'Release the device context
DeleteDC hNewDC
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LVL 1

Expert Comment

by:morgan_peat
ID: 15073
Check out the DIBSection class from vbAccelerator.com.  This contains all the functionality needed to manipulate DIB's.

http://www.vbaccelerator.com/codelib/gfx/cdibsect.zip
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LVL 32

Expert Comment

by:Erick37
ID: 15118
You can use the oleCreatePictureIndirect API to convert a bitmap handle into an OLE Picture object.  Here is an example which loads a bitmap from file and uses its handle to create a picture.

Option Explicit
Private Type PicBmp
    Size As Long
    Type As Long
    hBmp As Long
    hPal As Long
    Reserved As Long
End Type
Private Type GUID
    Data1 As Long
    Data2 As Integer
    Data3 As Integer
    Data4(7) As Byte
End Type
Private Declare Function OleCreatePictureIndirect Lib "olepro32.dll" _
    (PicDesc As PicBmp, RefIID As GUID, _
    ByVal fPictureOwnsHandle As Long, IPic As IPicture) As Long
   
'// For testing
Const LR_LOADFROMFILE = &H10
Const LR_DEFAULTSIZE = &H40
Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long
Private Declare Function LoadImage Lib "user32" Alias "LoadImageA" _
    (ByVal hInst As Long, ByVal lpsz As String, ByVal un1 As Long, ByVal n1 As Long, ByVal n2 As Long, ByVal un2 As Long) As Long
'//

Private Sub Command1_Click()
    Dim hBmp As Long
    'Get a bitmap handle
    hBmp = LoadImage(0, "c:\bitmap1.bmp", 0, 0, 0, LR_DEFAULTSIZE Or LR_LOADFROMFILE)
    'Create a picture from a bitmap handle
    Picture1.Picture = CreateBitmapPicture(hBmp)
    'Free the picture in memory
    Call DeleteObject(hBmp)
End Sub

Public Function CreateBitmapPicture(ByVal hBmp As Long, Optional ByVal hPal As Long) As Picture

    Dim r As Long
    Dim Pic As PicBmp
    ' IPicture requires a reference to "Standard OLE Types."
    Dim IPic As IPicture
    Dim IID_IDispatch As GUID
   
    If IsMissing(hPal) Then hPal = 0
    ' 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
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Author Comment

by:nickwoolley
ID: 21283
morgan_peat: This is a good site, and I've downloaded the DIB class but it will need me to spend some time looking through it.

Erick37: This was simple to setup and works well with Windows Bmp's.

My Problem is that I am working with a Bmp which is a DIB Device Independant Bitmap) in 'top-down' format with a negative height (Let's be honest I don't really know what I'm talking about!).

l99057j: Your comment looks as though it might do some conversion as it references CreateCompatibleBitmap??? But I would need a little more explanation from 'Create a device context......'
 
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LVL 2

Expert Comment

by:l99057j
ID: 21995
You need to BitBlt the image from the capture to the picture box.  BitBlt requires two Device Contexts... one for the source and one for the destination.  The captured image is not bound to a device context, it is simply the minimum amount of information necessary to define what the bitmap looks like.

CreateCompatibleDC creates a device context that has the same configuration (bits-per-pixel, planes, etc.) as the picturebox you are going to copy the bitmap to.  

SelectObject actually associates the bitmap with the device context you created so that it can be used in the BitBlt call.

The second select object de-associates the bitmap with the device context.

The DeleteDC call cleans everything up so we don't leak memory.

0
 

Author Comment

by:nickwoolley
ID: 22597
l99057j:

This looks good!

Does gdi32.dll come with NT, Win95, and Win98 do you know?

I've setup the code and when I run it I get the message no picture loaded, so I assume the BiBlt function is not working yet. MSDN notes for BitBlt say that the parameter  hdcSrc, which you have as hNewDC, is the handle to the source device context. Should hNewDC be hOldBitmap? I tried changing it but it did not work. I need to do some more testing on it

(I assume hBMPHandle is the handle I have which is returned from the capture card.)

I shall be back on the case Tuesday, have a good weekend everyone.
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LVL 2

Expert Comment

by:l99057j
ID: 22691
No hNewDC is correct.  The code ran on my machine. The only thing I left out is that hBMPHandle is indeed the handle returned from the capture card.  

Check the return values from all the API calls and you'll narrow down the problem.  I left them out for brevity.
0
 
LVL 2

Expert Comment

by:l99057j
ID: 22694
P.S. gdi32.dll is an integral part of windows.  If it isn't there, your application will be the least of the user's worries :)
0
 

Author Comment

by:nickwoolley
ID: 28151
l99057j: I tried loading the image using the Bmp handle from the capture card with your code and got the error message no image loaded. I then tried loading an image direct from a saved Bmp and passing to a handle with the your code adapted as below, but I get the same message.

What format of Bmp is your code compatible with?


Public Declare Function CreateCompatibleBitmap Lib "gdi32" (ByVal hdc As Long, ByVal nWidth As Long, ByVal nHeight As Long) As Long
Public 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
Public Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hdc As Long) As Long
Public Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long
Public Declare Function DeleteDC Lib "gdi32" (ByVal hdc As Long) As Long
Public Const SRCCOPY = &HCC0020 ' (DWORD) dest = source
Public Declare Function LoadImage Lib "user32" Alias "LoadImageA" (ByVal hInst As Long, ByVal lpsz As String, ByVal un1 As Long, ByVal n1 As Long, ByVal n2 As Long, ByVal un2 As Long) As Long


Sub Main()

'Some code

hBmp = LoadImage(0, "C:\dog.bmp", 0, 0, 0, &H40 Or &H10)
Call ConvertAndLoadDIBBmp(hBmp)

'Some more code

End Sub


Public Function ConvertAndLoadDIBBmp(hBmp As Long)

    Dim hNewDC As Long
    Dim hOldBitmap As Long
   
    On Error GoTo errHandler
   
    'Create a device context
    hNewDC = CreateCompatibleDC(Form1.Picture1.hdc)
    'hNewDC = CreateCompatibleDC(frmLive.imPhoto.hdc)
   
    'Select the bitmap into the device context...
    hOldBitmap = SelectObject(hNewDC, hBmp)
       
    'Draw the picture into the picture box...
    BitBlt Form1.Picture1.hdc, 0, 0, 20, 20, hNewDC, 0, 0, SRCCOPY
   
    Form1.Show
   
    'Deselect the bitmap
    SelectObject hNewDC, hOldBitmap
       
    'Release the device context
    DeleteDC hNewDC

End Function
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Author Comment

by:nickwoolley
ID: 66887
l99057j: Should your code work with a handle to a DIB Bmp as compared to a windows Bmp?
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Expert Comment

by:l99057j
ID: 67133
I copied my code from above, pasted it into VB and it worked fine... step through the code one line at a time and tell me which line is throwing the error.
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Author Comment

by:nickwoolley
ID: 72140
l99057j:You tried it with a DIB?
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Expert Comment

by:l99057j
ID: 73217
I tried your code which loaded a BMP from a file.  Since I don't have a video capture card or other easy way to create a DIB in memory I didn't try that.  Theoretically, once Windows has a handle to a bitmap you aren't supposed to have to worry about minor differences in structure.

P.S.  In reference to your earlier post about the top-down format with a negative height...  this just means that the image is stored "upside down".  If you want to learn all about bitmaps I recommend Nigel Thompsons's "Animation Techniques in Win32."  The book is aimed at game developers and was written before the advent of DirectX, so most of the game stuff is outdated.  But the early chapters tell all about bitmap structures, device contexts, and palettes.  A VERY good source of information.  I had to read these chapters four or five times before everything clicked, but I have yet to find anything better.  I know at one point you could find it on MSDN for free.
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Author Comment

by:nickwoolley
ID: 73315
l99057j: I can believe it works with a handle to a normal Bmp, infact I successfully tested one of the above code examples with a handle to a Windows Bmp. I think the problem lies with the format of the DIB. Can I send you the DIB file (163KB)?
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Author Comment

by:nickwoolley
ID: 6039640
It was the format of my BMP which was causing the problem.
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