IWICStream::InitializeFromFilename method (wincodec.h)

Article
02/22/2024

Initializes a stream from a particular file.

Syntax

HRESULT InitializeFromFilename(
  [in] LPCWSTR wzFileName,
  [in] DWORD   dwDesiredAccess
);

Parameters

[in] wzFileName

Type: LPCWSTR

The file used to initialize the stream.

[in] dwDesiredAccess

Type: DWORD

The desired file access mode.

Value	Meaning
GENERIC_READ	Read access.
GENERIC_WRITE	Write access.

Return value

Type: HRESULT

If this method succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.

Remarks

The IWICStream interface methods do not enable you to provide a file sharing option. To create a shared file stream for an image, use the SHCreateStreamOnFileEx function. This stream can then be used to create an IWICBitmapDecoder using the CreateDecoderFromStream method.

Examples

This example demonstrates the use of the InitializeFromFilename to create an image decoder.

    IWICImagingFactory *pFactory = NULL;
    IWICStream *pStream = NULL;
    IWICBitmapDecoder *pDecoder = NULL;

    HRESULT hr = CoCreateInstance(
                    CLSID_WICImagingFactory,
                    NULL,
                    CLSCTX_INPROC_SERVER,
                    IID_PPV_ARGS(&pFactory));

    // Create the stream.
    if (SUCCEEDED(hr))
    {
        hr = pFactory->CreateStream(&pStream);
    }

    // Initialize the stream from a specific file.
    if (SUCCEEDED(hr))
    {
        hr = pStream->InitializeFromFilename(L"test.jpg", GENERIC_READ);
    }    

    // Create a JPEG decoder.
    // Since the stream is created from the JPEG file, an explicit JPEG decoder
    // can be created using the generic IWICImagingFactory::CreateDecoder method.
    // However, use IWICImagingFactory::CreateDecoderFromStream method to auto
    // detect the stream and instantiate the appropriate codec.  
    if (SUCCEEDED(hr))
    {        
        hr = pFactory->CreateDecoder(
                GUID_ContainerFormatJpeg,   // Explicitly create a JPEG decoder.
                NULL,                       // No preferred vendor.
                &pDecoder);                 // Pointer to the decoder.
    } 

    // Initialize the decoder
    if (SUCCEEDED(hr))
    {
        hr = pDecoder->Initialize(
                pStream,                            // The stream to use.
                WICDecodeMetadataCacheOnDemand);    // Decode metadata when needed.
    } 

    // Process image frame.
    if (SUCCEEDED(hr))
    {
        UINT cFrames = 0;

        hr = pDecoder->GetFrameCount(&cFrames);

        if (SUCCEEDED(hr) && (cFrames > 0))
        {
            UINT width = 0, height = 0;        
            IWICBitmapFrameDecode *pBitmapFrame = NULL;

            hr = pDecoder->GetFrame(0, &pBitmapFrame);

            if (SUCCEEDED(hr))
            {
                // Do something with the frame here.
            }

            if (pBitmapFrame)
            {
                pBitmapFrame->Release();
            }
        }
    } 

    if (pStream)
    {
        pStream->Release();
    }

    if (pFactory)
    {
        pFactory->Release();
    }

    if (pDecoder)
    {
        pDecoder->Release();
    }

Requirements

Requirement	Value
Minimum supported client	Windows XP with SP2, Windows Vista [desktop apps \| UWP apps]
Minimum supported server	Windows Server 2008 [desktop apps \| UWP apps]
Target Platform	Windows
Header	wincodec.h
Library	Windowscodecs.lib
DLL	Windowscodecs.dll

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