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Drawing a picture in a memory DC?

I have a picture in a CPictureHolder, I need to render this picture in a memory DC then use the memory DC in a  BitBlt function to draw parts of it on the screen.
I wrote some code but it is not working, what did I miss or is it not a valid idea?

void CControl::OnDraw(CDC* pcdc, const CRect& crcBounds, const CRect& crcInvalid)
{
MemoryDC.CreateCompatibleDC(pcdc);
Picture.Render(MemoryDC, crcBounds, crcBounds);
}

cdc->BitBlt(0, 0, nWidth, nHeight, &MemoryDC, 0, 0, SRCAND);
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Daed
Asked:
Daed
1 Solution
 
gilad_noCommented:
You need to create and attach a bitmap to the memory dc before you use it.

{
CDC memoryDC;
memoryDC.CreateCompatibleDC(pcdc);
CBitmap bitmap;
bitmap.CreateCompatibleBitmap(pcdc,nWidth,nHeight);
CBitmap *oldb=memoryDC.SelectObject(&bitmap);

// now you can work on your memoryDC


pcdc->BitBlt(0,0,nWidth,nHeight,0,0,SRCAND);
memoryDC.SelectObject(oldb);
}

Since you create the memoryDC in the stack, you don't need to destroy it by yourself
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