Drawing to a bitmap.

Posted on 2002-05-10
Medium Priority
Last Modified: 2013-11-20
Hi everybody.

 I would like to know how to create a Bitmap which contains the entire view and all the objects displayed n it.

 Note that I'm not asking for a screen capture: the whole idea is drawing the scene n a bitmap instead of n the
screen (as OnDraw does), perhaps creating previously a device context.

I already know how to save a bitmap to a file so do no mess with this point. Please make your answers as explicit
as possible. Code would help.

Hope you know what I mean.

Question by:Iraklis
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Author Comment

ID: 7003156
Is this question so difficult. Here you are more points.
LVL 12

Expert Comment

ID: 7003196
it isn`t so difficult
in general you have to make several steps:
1. create memory device context
2. bitmap
3. Select bitmap into the memory DC
4. draw your view using this memory DC
5. deselect bitmap
6. You have bitmap and you can save it to the disk

code example:
CDC dcMem;
CClientDC dcClient(this);
CRect rc;
CBitmap bmView;
bmView.CreateCompatibleBitmap(&dcMem, rc.Width(), rc.Height());
CBitmap* pbmOld = dcMem.SelectObject(&bmView);
OnDraw(&dcMem); // draw in this context
// now you have bitmap
StoreBitmap(&bmView);// save it to disk

Author Comment

ID: 7004706
Hi, Miguel.

I forgot to mention (my apologies for this) that I'm using a CSCrollView of wich map mode is set to MM_LOMETRIC. Therefore some functions such OnPrepareDC, LPtoDP and SetMapMode must be added.

On the other hand I doubt about the first parameter in
"CreateCompatibleBitmap". Should it be dcClient instead?

I can add more points if required.


Expert Comment

ID: 7005058
I don't understand you clearly.Are you want to convert a window which maybe have subwindow to a bitmap? If so, see this:

HBITMAP hBitMap = 0;
BOOL GetWndBmp()

   HDC hCatchDC = CreateCompatibleDC(NULL);
   HDC hTempDC = ::GetDC(NULL);
   RECT rect;
   ::GetWindowRect(m_hWnd/*your window handle*/, &rect);
   int nWidth = rect.right - rect.left;
   int nHeight = rect.bottom - rect.top;
   hBitMap = CreateCompatibleBitmap(hTempDC, nWidth, nHeight);
   HBITMAP oldbmp = (HBITMAP)SelectObject(hCatchDC, hBitMap);
   // let the window draw itself on my hCatchDC

   ::ReleaseDC(NULL, hTempDC);

   SelectObject(hCatchDC, oldbmp);
   return TRUE;

LVL 12

Accepted Solution

migel earned 753 total points
ID: 7005361
of course you must use clientDC
bmView.CreateCompatibleBitmap(&dcClient, rc.Width(), rc.Height());
and add
before OnDraw(&dcMem);
in general all preparation for drawing such as: SetMapMode, SetViewportExt and so on, you must do in the OnPrepareDC so no other preparation in my function need.

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