Saving a screenshot to a buffer

Since you are already using GDI+, you can simply call the LockBits method of the Bitmap class to give you the bitmap in whatever format you desire.

http://msdn.microsoft.com/en-us/library/ms536298(VS.85).aspx

It seems to be the right function. I'm trying to get all the bitmap's content as a jped and instead of saving it to a file i want to save those bytes into a buffer. Then just dump the buffer to either a flat file or to the stdout.
the GetEncoderClsid() function on the code that i posted earlier is here below.

any idea of the code for doing this? I mean, from the example on the MSDN i can learn a bit about how to read that data but i am still having trouble putting all those bytes into a buffer that i can use.

thanks

int GetEncoderClsid(WCHAR *format, CLSID *pClsid)
{
	unsigned int num = 0,  size = 0;
	GetImageEncodersSize(&num, &size);
	if(size == 0) return -1;
	ImageCodecInfo *pImageCodecInfo = (ImageCodecInfo *)(malloc(size));
	if(pImageCodecInfo == NULL) return -1;
	GetImageEncoders(num, size, pImageCodecInfo);
	for(unsigned int j = 0; j < num; ++j){
		if(wcscmp(pImageCodecInfo[j].MimeType, format) == 0){
			*pClsid = pImageCodecInfo[j].Clsid;
			free(pImageCodecInfo);
			return j;
		}    
	}
	free(pImageCodecInfo);
	return -1;
}

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So do you want the jpeg output saved to a memory block?  If that is the case, you should use the Save method which takes a stream (instead of a file name).

http://msdn.microsoft.com/en-us/library/ms535406(VS.85).aspx

To create a memory stream, you can use CreateStreamOnHGlobal:

http://msdn.microsoft.com/en-us/library/ms535406(VS.85).aspx

I messed up the link to the CreateStreamOnHGlobal.  Here is the correct link:

http://msdn.microsoft.com/en-us/library/aa378980.aspx

Thanks,

I run into those functions after your first post as I was searching the gdiplus API.
Maybe it is my lack of experience with COM, or the fact that i never got any of the MSDN code to work or the fact that I don't understand the way the MSDN explains anything (i'm an old time UNIX programmer).
In any case, i still can't find a way to save that image to a buffer.
If you can, could you please post some working code that can do this?

I appreciate the help

Come now, it is not that hard.  (I am a UNIX programmer from way back myself).  Attached is a code snippet which shows you how you might do it.

HGLOBAL	hMem;
 
if (hMem = GlobalAlloc(GMEM_MOVEABLE, 0))
{
    IStream * pStream;
 
    if (CreateStreamOnHGlobal(hMem, FALSE, &pStream) == S_OK)
    {
        Status result;
 
        result = pBitmap->Save(pStream, pEncoder);
 
        pStream->Release();
 
        if (result == Ok)
        {
            unsigned char * pBytes;
 
            if (pBytes = (unsigned char *) GlobalLock(hMem))
            {
                /*
                 * pBytes now points to your image file in memory
                 *  in whatever format was specified by your encoder
                 *	  parameter.
                 */
            }
        }
    }
}

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error C2664: 'Gdiplus::Status Gdiplus::Image::Save(const WCHAR *,const CLSID *,const Gdiplus::EncoderParameters *)' : cannot convert parameter 1 from 'IStream *' to 'const WCHAR *'
1>        Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

I am casting it but i still get the error. besides, you are placing inside the save something i assume is EncoderParameters  (the variable is pEncoder). Now, maybe i am missing something but that won't point to the actual bitmap data.
anyway, it's a mess to try to putt hat code inside the original function since i am guessing most of the variables on your code.

ok, this code below is my try. it compiles but it just does nothing. I debug it but nothing gets saved anywhere.

	if (hMem = GlobalAlloc(GMEM_MOVEABLE, 0))
	{
		IStream * pStream;
	 
		if (CreateStreamOnHGlobal(hMem, FALSE, &pStream) == S_OK)
		{
			
			// save the buffer to a file	
			pScreenShot = new Bitmap(hbmCapture, (HPALETTE)NULL);
			EncoderParameters encoderParams;
			encoderParams.Count = 1;
			encoderParams.Parameter[0].NumberOfValues = 1;
			encoderParams.Parameter[0].Guid  = EncoderQuality;
			encoderParams.Parameter[0].Type  = EncoderParameterValueTypeLong;
			encoderParams.Parameter[0].Value = &uQuality;
			GetEncoderClsid(L"image/jpeg", &imageCLSID);
	 
			result = pScreenShot->Save(pStream, &imageCLSID, &encoderParams);
	 
			pStream->Release();
	 
			//if (result == Ok)
			//{
				unsigned char * pBytes;
	 
				if (pBytes = (unsigned char *) GlobalLock(hMem))
				{
					/*
					 * pBytes now points to your image file in memory
					 *  in whatever format was specified by your encoder
					 *        parameter.
					 */
					printf("bitmap = %s\n", pBytes);
				}
				else
				{
					printf("error GlobalLock. Last err: %d\n", GetLastError());
					return 0;
				}
			//}
 
		}
		else
		{
			printf("error CreateStreamOnHGlobal. Last err: %d\n", GetLastError());
			return 0;
		}
	}
	else
	{
		printf("error GlobalAlloc. Last err: %d\n", GetLastError());
		return 0;
	}
 
	return result;

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Is the save returning OK (I notice that you have the check commented out)?  I am not really sure why you are trying to print the string returned by GlobalLock.  It is NOT an ASCII string that you can print in that manner, rather it is a pointer to the binary JPEG file.

Perhaps if you tell me exactly what you are trying to do, I might be able to suggest something.

the printf was there for the purpose of testing.
what i need to do is to grab that jpeg data, copy it to an array to whatever and wither save it to a file or add it to another buffer. That's all.
thanks for the help

great! thanks!

thanks so much for all the effort.