WriteableBitmap.PixelBuffer Property

Reference

Definition

Namespace:: Windows.UI.Xaml.Media.Imaging

Important

Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

Edit

Gets an access for the direct buffer where each pixel of the WriteableBitmap is written to.

public:
 property IBuffer ^ PixelBuffer { IBuffer ^ get(); };

IBuffer PixelBuffer();

public IBuffer PixelBuffer { get; }

var iBuffer = writeableBitmap.pixelBuffer;

Public ReadOnly Property PixelBuffer As IBuffer

Property Value

IBuffer

A reference to the pixel buffer.

Examples

This code example uses the PixelBuffer property of WriteableBitmap to write to its pixel content.

The C# example comes from a larger code sample—the SDK XAML images sample. The C# code shown is part of a transcoding scenario that eventually uses the WriteableBitmap as an Image.Source value, and displays the image.

The examples in the other languages are a little more scoped and/or self-contained.

using (IRandomAccessStream fileStream = await file.OpenAsync(Windows.Storage.FileAccessMode.Read)) 
{
    BitmapDecoder decoder = await BitmapDecoder.CreateAsync(fileStream); 
    // Scale image to appropriate size 
    BitmapTransform transform = new BitmapTransform() {  
        ScaledWidth = Convert.ToUInt32(Scenario4WriteableBitmap.PixelWidth), 
        ScaledHeight = Convert.ToUInt32(Scenario4WriteableBitmap.PixelHeight)
    }; 
    PixelDataProvider pixelData = await decoder.GetPixelDataAsync( 
        BitmapPixelFormat.Bgra8, // WriteableBitmap uses BGRA format 
        BitmapAlphaMode.Straight, 
        transform, 
        ExifOrientationMode.IgnoreExifOrientation, // This sample ignores Exif orientation 
        ColorManagementMode.DoNotColorManage
    ); 

    // An array containing the decoded image data, which could be modified before being displayed 
    byte[] sourcePixels = pixelData.DetachPixelData(); 

    // Open a stream to copy the image contents to the WriteableBitmap's pixel buffer 
    using (Stream stream = Scenario4WriteableBitmap.PixelBuffer.AsStream()) 
    { 
        await stream.WriteAsync(sourcePixels, 0, sourcePixels.Length); 
    }                     
}

// You'll need to add the Pictures Library capability to your Package.appxmanifest file.

// MainPage.xaml
...
<Image x:Name="anyExampleImage" Width="100" Height="100"/>
...

// pch.h
...
#include <winrt/Windows.Graphics.Imaging.h>
#include <winrt/Windows.Storage.Streams.h>
#include <winrt/Windows.UI.Xaml.Media.Imaging.h>
struct __declspec(uuid("905a0fef-bc53-11df-8c49-001e4fc686da")) IBufferByteAccess : ::IUnknown
{
    virtual HRESULT __stdcall Buffer(uint8_t** value) = 0;
};
...

// MainPage.h
...
struct MainPage : MainPageT<MainPage>
{
    ...
    Windows::Foundation::IAsyncAction ClickHandler(Windows::Foundation::IInspectable const&, Windows::UI::Xaml::RoutedEventArgs const&);
private:
    Windows::UI::Xaml::Media::Imaging::WriteableBitmap m_writeableBitmap{ nullptr };
};
...

// MainPage.cpp
...
Windows::Foundation::IAsyncAction MainPage::ClickHandler(IInspectable const&, RoutedEventArgs const&)
{
    uint32_t scaledSize = 100;
    m_writeableBitmap = Windows::UI::Xaml::Media::Imaging::WriteableBitmap(scaledSize, scaledSize);

    Windows::Storage::StorageFolder picturesFolder{ Windows::Storage::KnownFolders::PicturesLibrary() };
    auto anyExampleImageFile{ co_await picturesFolder.GetFileAsync(L"anyexampleimage.png") };
    Windows::Storage::Streams::IRandomAccessStream fileStream{ co_await anyExampleImageFile.OpenAsync(Windows::Storage::FileAccessMode::Read) };
    auto decoder{ co_await Windows::Graphics::Imaging::BitmapDecoder::CreateAsync(fileStream) };

    // Scale the image to the appropriate size.
    Windows::Graphics::Imaging::BitmapTransform transform;
    transform.ScaledWidth(scaledSize);
    transform.ScaledHeight(scaledSize);

    Windows::Graphics::Imaging::PixelDataProvider pixelData{ co_await decoder.GetPixelDataAsync(
        Windows::Graphics::Imaging::BitmapPixelFormat::Bgra8, // WriteableBitmap uses BGRA format 
        Windows::Graphics::Imaging::BitmapAlphaMode::Straight,
        transform,
        Windows::Graphics::Imaging::ExifOrientationMode::IgnoreExifOrientation, // This sample ignores Exif orientation 
        Windows::Graphics::Imaging::ColorManagementMode::DoNotColorManage
    ) };

    // An array containing the decoded image data, which could be modified before being displayed 
    winrt::com_array<uint8_t> sourcePixels{ pixelData.DetachPixelData() };

    // COMMENT OUT EXACTLY ONE OF TECHNIQUE 1/2
    // TECHNIQUE 1; QI for IBufferByteAccess.
    auto bufferByteAccess{ m_writeableBitmap.PixelBuffer().as<::IBufferByteAccess>() };
    uint8_t * pTargetBytes{ nullptr };
    bufferByteAccess->Buffer(&pTargetBytes);
    // TECHNIQUE 2; use a C++/WinRT helper function (and delete the definition of IBufferByteAccess in pch.h).
    //uint8_t * pTargetBytes{ m_writeableBitmap.PixelBuffer().data() };

    for (auto & element : sourcePixels)
    {
        *(pTargetBytes++) = element;
    }

    anyExampleImage().Source(m_writeableBitmap);
}
...

// pch.h
...
#include <robuffer.h>
...

// MainPage.xaml.cpp
auto writeableBitmap{ ref new Windows::UI::Xaml::Media::Imaging::WriteableBitmap(100, 100) };

::IUnknown* pUnk{ reinterpret_cast<IUnknown*>(writeableBitmap->PixelBuffer) };
Microsoft::WRL::ComPtr<Windows::Storage::Streams::IBufferByteAccess> bufferByteAccess;
HRESULT hr{ pUnk->QueryInterface(IID_PPV_ARGS(&bufferByteAccess)) };

byte *pBuffer{ nullptr };
bufferByteAccess->Buffer(&pBuffer);

// Now, write into the WriteableBitmap by using pBuffer. For example, make the first pixel red.
*pBuffer = 0xFF; ++pBuffer;
*pBuffer = 0xFF; ++pBuffer;
*pBuffer = 0x0; ++pBuffer;
*pBuffer = 0x0;

Remarks

Note

Use the Language picker (near the title) to choose a programming language for the code example.

The IBuffer returned by PixelBuffer can't be written to directly. But you can use language-specific techniques to write to the underlying pixel content in the buffer.

To access the pixel content from C# or Microsoft Visual Basic, you can use the WindowsRuntimeBufferExtensions.AsStream method to access the underlying buffer as a stream. This is shown in the C# code example.
To access the pixel content from C++/WinRT, you have three alternatives. As long as you're not using namespace winrt;, then you can include the SDK header file robuffer.h to bring in the definition of the IBufferByteAccess COM interface. However, since using namespace winrt; is very common, you can alternatively define the IBufferByteAccess interface in one place in your project (see the C++/WinRT code example to see how). Once IBufferByteAccess is defined, using either of those two techniques, you can query PixelBuffer for an instance of IBufferByteAccess. You then call the IBufferByteAccess::Buffer method to retrieve a pointer to the buffer of bytes that represents the pixel content. This is shown in the C++/WinRT code example. The third alternative (also shown in the C++/WinRT code example) is to avoid using IBufferByteAccess altogether by retrieving the uint8_t* that's returned from a helper function that you can call with WriteableBitmap.PixelBuffer().data().
To access the pixel content from C++/CX, you can query PixelBuffer for the IBufferByteAccess interface, which is a COM interface. Include robuffer.h. You can then call the the IBufferByteAccess::Buffer method to retrieve a pointer to the buffer of bytes that represents the pixel content. This is shown in the C++/CX code example.

Applies to

Jaa

WriteableBitmap.PixelBuffer Property

Definition

Property Value

Examples

Remarks

Applies to

See also

Palaute

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