C / C++ / MFC

4-Oct-01 6:44

I'm capturing a frame from a video stream. The data is being captured (I've verified that) as a 24-bit image. Part of the data being "captured" is the contents of the BITMAPINFOHEADER struct (again, this struct contains viable data).

I want to take this image and store it to the clipboard as a DIB.

Why doesn't this code work?

BITMAPINFO bmi;
memset(&bmi, 0, sizeof(BITMAPINFO));
bmi.bmiHeader = cb.bih; // the cb struct is populated by the capture callback

HDC hMemDC = CreateCompatibleDC(NULL);
HBITMAP hBitmap = CreateDIBitmap(hMemDC, &bmi.bmiHeader, CBM_INIT, cb.pBuffer, &bmi, DIB_RGB_COLORS);

if (OpenClipboard(NULL))
{
   EmptyClipboard();
   if (!SetClipboardData(CF_DIB, hBitmap))
   {
      // show error message
   }
   CloseClipboard();
}

It always says that the hBitmap handle is invalid when I try to call SetClipboardData(). The hBitmap isn't NULL.

C^hris L^osinger4-Oct-01 7:00

4-Oct-01 7:00

try using a real DC (instead of NULL) in your CreateCompatibleDC call. i find that these CreateCompatible things often only work with a real DC.

-c

------------------------------
Smaller Animals Software, Inc.
http://www.smalleranimals.com

#realJSOP4-Oct-01 7:18

4-Oct-01 7:18

I tried the CreateCompatibleDC method, and the results are the same.

The SDK documentation says that if you pass NULL to CreateCompatibleDC, you get a screen DC. Why isn't that good enough?

Confused | :confused:

C^hris L^osinger4-Oct-01 7:29

4-Oct-01 7:29

that might be true..

i only metion that becaseu i find that doing something like this:

CDC memDC;
memDC.CreateCompatibleDC(pRealDC);
CBitmap memBMP;
memBMP.CreateCompatibleBitmap(memDC, ...);

will often fail (i get a monochrome bitmap or something equally perverse). To make it work I have to use pRealDC in the CreateCompatibleBitmap call. using the 'compatible' DC screws things up.

so, as a rule, i always use a real DC (from GetDC(NULL), or a paint DC or a CClientDC) in these functions.

just a thought.

also, when i copy DIBs to the clipboard, i do it like this:

HGLOBAL CISImage::MakeClipboardDIB()
{
   HGLOBAL hDIB = MakeDIB();
   
   HGLOBAL hCBDIB = NULL;
   if (hDIB)
   {
      DWORD dwSize = GlobalSize(hDIB);
      hCBDIB = GlobalAlloc(GMEM_MOVEABLE | GMEM_DDESHARE, dwSize);
      if (hCBDIB)
      {
         BYTE *pCBDIB = (BYTE *)GlobalLock(hCBDIB);
         memcpy(pCBDIB, (BYTE *)hDIB, dwSize);
         GlobalUnlock(hCBDIB);
      }
      
      GlobalFree(hDIB);
   }
   
   return hCBDIB;
}

...

if (OpenClipboard(AfxGetMainWnd()->m_hWnd))
{
   CISImage img; 

   ...put something in img...etc.

   HGLOBAL hDib = img.MakeClipboardDIB();
   
   HANDLE res = SetClipboardData(CF_DIB, hDib);
   ASSERT(res);

   CloseClipboard();
}

-c

------------------------------
Smaller Animals Software, Inc.
http://www.smalleranimals.com

#realJSOP4-Oct-01 7:57

4-Oct-01 7:57

I can't find any reference to MakeDIB except for a MSDN sample app, and it requires parameters.

C^hris L^osinger4-Oct-01 7:59

4-Oct-01 7:59

yeah. that's my own function. it just creates a typical BITMAPINFOHEADER and image data DIB. i'm assuming you already have a DIB floating around somewhere.

-c

------------------------------
Smaller Animals Software, Inc.
http://www.smalleranimals.com

#realJSOP4-Oct-01 8:19

4-Oct-01 8:19

Wel, I have a populated BITMAPINFOHEADER and a shitload of captured bytes... Smile | :)

I've been trying to make a DIB that can be stored to the clipboard. Trouble is, I don't know what I've done right, and what I've done wrong. Smile | :)

Why does something like this have to be so hard in a *graphical* operating system?

C^hris L^osinger4-Oct-01 8:23

4-Oct-01 8:23

sounds like you've got a DIB. have you tried displaying it (with something like StretchDIBits), just to be sure?

// Get source bitmap info
BITMAPINFO *pBMInfo = (LPBITMAPINFO)pDIB ;

// assumes a generic 24bit DIB
LPVOID lpDIBBits = (LPVOID)(pDIB + pBMInfo->bmiHeader.biSize);

// now blast it to the CDC passed in.
// lines returns the number of lines actually displayed
UINT32 lines = StretchDIBits(outHDC,
                     xPos, yPos,
                     outWidth, outHeight,
                     0,0,
                     inWidth,
                     inHeight,
                     lpDIBBits,
                     pBMInfo,
                     DIB_RGB_COLORS,
                     SRCCOPY);

that's the easiest way to tell if your DIB is correct/well-formed.

-c

------------------------------
Smaller Animals Software, Inc.
http://www.smalleranimals.com

#realJSOP4-Oct-01 8:42

4-Oct-01 8:42

Yup, when I do a StrechDIBits, lines is equal to bmiHeader.biHeight.

C^hris L^osinger4-Oct-01 8:45

4-Oct-01 8:45

hmmm.. have you tried the clipboard code i posted above?

-c

------------------------------
Smaller Animals Software, Inc.
http://www.smalleranimals.com

#realJSOP4-Oct-01 8:49

4-Oct-01 8:49

not yet - in the process tho...

Tomasz Sowinski4-Oct-01 7:10

Tomasz Sowinski

4-Oct-01 7:10

You can't just pass a dib handle to SetClipboardData - that would be too easy. You have to copy the contents into a global memory block and pass the handle of this memory block to SetClipboardData. DIBLOOK sample may be helpful; have a look at CopyHandle helper.

Tomasz Sowinski -- http://www.shooltz.com

#realJSOP4-Oct-01 7:16

4-Oct-01 7:16

I've already tried the CopyHandle() method, and I get the same results.