Save bitmap to global memory

Question

I have a Bitmap object and want to create a bmp-file in a global memory using the save Method with an Istream Interface. How can I obtain the size of the bmp file before streaming it to my global memory??

Answer 1

Chicken-and-egg problem, you don't really know until you've serialized the bitmap.  You can certainly calculate the size from the BITMAPINFOHEADER.  But avoid getting that wrong by using an IStream implementation that knows how to expand the memory allocation when necessary.  CreateStreamOnHGlobal() fits that bill.

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Hans Passant.

Answer 2

The Bitmap has a width, height and bpp. The size depends on the specific format, which is documented in many places.

Answer 3

Was successful with CreateStreamOnHGlobal(...) Thanx!

Bitmap *bitmap;

HGLOBAL hMem;

IStream *stream;

LPVOID pImage, pMem;

CLSID encoderCLSID;

DWORD bmpSize;

bitmap = new Bitmap((**phAreaData)->PictDef.PictWidth,

(**phAreaData)->PictDef.PictHeight,

PixelFormat32bppPARGB);

.... // fill the bitmap

// calculate bitmap size

bmpSize = bitmap->GetWidth() * bitmap->GetHeight() * 4 + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

// Create a global memory

hMem = ::GlobalAlloc(GMEM_MOVEABLE, bmpSize);

// Create a stream object from the global memory

CreateStreamOnHGlobal(hMem, true, &stream);

// Save bitmap to iStream

GetEncoderClsid(L"image/bmp", &encoderCLSID);

bitmap->Save(stream, &encoderCLSID);

pMem = ::GlobalLock(hMem);

// custom function

pict = CreatePicture(pMem, bmpSize);

::GlobalUnlock(hMem);

stream->Release();