WriteableBitmap.PixelBuffer 属性

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

IBuffer PixelBuffer();

public IBuffer PixelBuffer { get; }

var iBuffer = writeableBitmap.pixelBuffer;

Public ReadOnly Property PixelBuffer As IBuffer

属性值

对像素缓冲区的引用。

示例

此代码示例使用 WriteableBitmap 的 PixelBuffer 属性写入其像素内容。

C# 示例来自一个更大的代码示例- SDK XAML 图像示例。 显示的 C# 代码是转码方案的一部分，该方案最终使用 WriteableBitmap 作为 Image.Source 值并显示图像。

其他语言中的示例的范围和/或自包含性略有一些。

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;

注解

无法将 PixelBuffer 返回的 IBuffer 直接写入。 但可以使用特定于语言的技术写入缓冲区中的基础像素内容。

• 若要从 C# 或 Microsoft Visual Basic 访问像素内容，可以使用 WindowsRuntimeBufferExtensions.AsStream 方法 以流的形式访问基础缓冲区。 C# 代码示例中显示了这一点。
• 若要从 C++/WinRT 访问像素内容，有三种替代方法。 只要不是 using namespace winrt;，就可以包含 SDK 头文件 robuffer.h ，以引入 IBufferByteAccess COM 接口的定义。 但是，由于 using namespace winrt; 很常见，因此还可以在项目中的一个位置定义 IBufferByteAccess 接口 (请参阅 C++/WinRT 代码示例，了解) 方式。 定义 IBufferByteAccess 后，可以使用这两种技术之一查询 PixelBuffer 以获取 IBufferByteAccess 实例。 然后调用 IBufferByteAccess：：Buffer 方法 以检索指向表示像素内容的字节缓冲区的指针。 这在 C++/WinRT 代码示例中显示。 C++/WinRT 代码示例) 中显示的第三个替代 (是，通过检索uint8_t*可从可使用 调用WriteableBitmap.PixelBuffer().data()的帮助程序函数返回的 ，从而避免使用 IBufferByteAccess。
• 若要从 C++/CX 访问像素内容，可以查询 PixelBuffer 以获取 IBufferByteAccess 接口，该接口是 COM 接口。 添加 robuffer.h。 然后，可以调用 IBufferByteAccess：：Buffer 方法来 检索指向表示像素内容的字节缓冲区的指针。 C++/CX 代码示例中显示了这一点。

适用于

另请参阅

• BitmapSource
• BitmapDecoder
• IBuffer
• Windows.Graphics.Imaging 命名空间
• XAML 图像示例