无XAML控件/窗口下，在Direct2D中绘制WinRT Composition Visual并取像素

我正尝试在Direct2D应用中绘制cppwinrt Lottie动画，但不清楚具体实现方法。请问能否不借助XAML控件和窗口，绘制WinRT::Windows::UI::Composition::Visual动画并获取像素数据？

我已成功加载Lottie动画，代码如下：

auto bmv = winrt::make<AnimatedVisuals::LottieLogo1>();
auto avptr = bmv.TryCreateAnimatedVisual(compositor, diags);
        
m_visual = avptr.RootVisual();

auto progressAnimation = compositor.CreateScalarKeyFrameAnimation();
progressAnimation.Duration(std::chrono::seconds(5));
progressAnimation.IterationBehavior(winrt::Windows::UI::Composition::AnimationIterationBehavior::Forever);
progressAnimation.Direction(winrt::Windows::UI::Composition::AnimationDirection::Alternate);
auto linearEasing = compositor.CreateLinearEasingFunction();
progressAnimation.InsertKeyFrame(0, 0, linearEasing);
progressAnimation.InsertKeyFrame(1, 1, linearEasing);

m_visual.Properties().StartAnimation(L"Progress", progressAnimation);

现在我需要将该动画绘制到D2D Bitmap上或获取像素信息。我尝试创建帧池，但未收到帧，相关代码如下：

winrt::Windows::Graphics::DirectX::Direct3D11::IDirect3DDevice m_device;
{
    auto d3dDevice = CreateD3DDevice();
    auto dxgiDevice = d3dDevice.as<IDXGIDevice>();
    if (dxgiDevice)
    {
        hr = CreateDirect3DDevice(dxgiDevice.get(), &m_device);
    }
}

m_framePool = winrt::Windows::Graphics::Capture::Direct3D11CaptureFramePool::Create(
    m_device,
    winrt::Windows::Graphics::DirectX::DirectXPixelFormat::B8G8R8A8UIntNormalized,
    3,
    winrt::Windows::Graphics::SizeInt32({ 400, 400 }));

m_session = m_framePool.CreateCaptureSession(winrt::Windows::Graphics::Capture::GraphicsCaptureItem::CreateFromVisual(m_visual));

m_frameArrived = m_framePool.FrameArrived(winrt::auto_revoke, { this, &CLottie::OnFrameArrived });

m_session.StartCapture();

再次询问：能否不使用XAML控件和窗口实现该动画的绘制与数据获取？

更新内容 #

auto controller = CreateDispatcherQueueController();

winrt::Windows::UI::Composition::Compositor compositor{};   

CComPtr<ABI::Windows::UI::Composition::ICompositorInterop> compositorInterop;

hr = winrt::get_unknown(compositor)->QueryInterface(&compositorInterop);
winrt::com_ptr<ABI::Windows::UI::Composition::ICompositionGraphicsDevice> device = nullptr;

hr = compositorInterop->CreateGraphicsDevice(direct2dDevice, device.put());
auto gDevice = device.as<winrt::Windows::UI::Composition::CompositionGraphicsDevice>();

winrt::Windows::Foundation::Size surfaceSize{ 400, 400 };
winrt::Windows::UI::Composition::CompositionDrawingSurface surface = gDevice.CreateDrawingSurface(surfaceSize,
    winrt::Windows::Graphics::DirectX::DirectXPixelFormat::B8G8R8A8UIntNormalized,
    winrt::Windows::Graphics::DirectX::DirectXAlphaMode::Premultiplied);

auto brush = compositor.CreateSurfaceBrush(surface);
float width = 400.0f, height = 400.0f;

winrt::Windows::UI::Composition::SpriteVisual visual = compositor.CreateSpriteVisual();
visual.Brush(brush);
visual.Size({ width, height });

winrt::Windows::UI::Composition::ShapeVisual shape = compositor.CreateShapeVisual();
shape.Size({ 100.0f,100.0f });
auto circleGeometry = compositor.CreateEllipseGeometry();
circleGeometry.Radius(winrt::Windows::Foundation::Numerics::float2(30, 30));
auto circleShape = compositor.CreateSpriteShape(circleGeometry);
circleShape.FillBrush(compositor.CreateColorBrush(winrt::Windows::UI::Colors::Orange()));
circleShape.Offset(winrt::Windows::Foundation::Numerics::float2(50, 50));
shape.Shapes().Append(circleShape);
visual.Children().InsertAtTop(shape);

auto surfaceInterop = surface.as<ABI::Windows::UI::Composition::ICompositionDrawingSurfaceInterop>();

CComPtr<ID2D1DeviceContext> dc;
POINT offset = {};

hr = surfaceInterop->BeginDraw(nullptr,
    __uuidof(dc),
    reinterpret_cast<void**>(&dc),
    &offset);

CComPtr<ID2D1Bitmap1> bitmap = nullptr;
D2D1_BITMAP_PROPERTIES1 prop;
prop.pixelFormat.format = DXGI_FORMAT_B8G8R8A8_UNORM;
prop.pixelFormat.alphaMode = D2D1_ALPHA_MODE_PREMULTIPLIED;
prop.dpiX = 96;
prop.dpiY = 96;
prop.bitmapOptions = D2D1_BITMAP_OPTIONS_CPU_READ | D2D1_BITMAP_OPTIONS_CANNOT_DRAW;
prop.colorContext = NULL;

hr = dc->CreateBitmap(D2D1::SizeU(width, height), NULL, 0, prop, &bitmap);

hr = bitmap->CopyFromRenderTarget(NULL, dc, NULL);

hr = surfaceInterop->EndDraw();

完全可以不依赖XAML控件和窗口实现需求，核心思路是利用Composition离线渲染结合Direct3D/Direct2D互操作，或者修正Graphics Capture的使用问题。以下是两种可行方案：

方案一：修正Graphics Capture获取帧失败问题 #

你当前用Graphics Capture没收到帧，核心原因是GraphicsCaptureItem::CreateFromVisual要求目标Visual必须属于一个有激活的Composition Host的树（即使是离线Host），且需要确保Compositor和DispatcherQueue正确初始化。

修复步骤： #

1. 确保DispatcherQueue生命周期稳定
   离线使用Composition必须先创建DispatcherQueue，你更新代码里的CreateDispatcherQueueController()是对的，但要确保它的生命周期和Compositor、Visual树一致，不能提前销毁。

2. 创建离线Composition目标并挂载Lottie Visual
   必须把Lottie Visual挂载到根ContainerVisual，并关联到离线CompositionTarget：

   // 初始化Compositor后创建离线目标
   auto target = compositor.CreateCompositionTargetForOffscreen();
   auto rootVisual = compositor.CreateContainerVisual();
   rootVisual.Size({400, 400});
   // 将你的Lottie Visual添加到根视觉树
   rootVisual.Children().InsertAtTop(m_visual);
   target.Root(rootVisual);
   

3. 重新创建Capture Session
   用CreateFromVisual传入rootVisual来创建CaptureItem，此时帧池就能正常收到渲染后的帧。

4. 在FrameArrived中读取像素数据
   在回调里通过帧的Direct3DSurface拿到ID3D11Texture2D，映射到CPU读取像素：

   void CLottie::OnFrameArrived(winrt::Windows::Graphics::Capture::Direct3D11CaptureFramePool const& sender, winrt::Windows::Foundation::IInspectable const&)
   {
       auto frame = sender.TryGetNextFrame();
       auto d3dSurface = frame.Direct3DSurface();
       winrt::com_ptr<ID3D11Texture2D> texture;
       winrt::check_hresult(d3dSurface.as<::Windows::Graphics::DirectX::Direct3D11::IDirect3DDxgiInterfaceAccess>()->GetInterface(__uuidof(texture), texture.put_void()));
   
       // 映射纹理到CPU
       D3D11_MAPPED_SUBRESOURCE mapped{};
       winrt::check_hresult(m_d3dDeviceContext->Map(texture.get(), 0, D3D11_MAP_READ, 0, &mapped));
       // mapped.pData即为B8G8R8A8_UNORM格式的像素数据
       // 处理数据...
       m_d3dDeviceContext->Unmap(texture.get(), 0);
   }
   

方案二：直接将Composition Visual渲染到D2D Bitmap #

利用Composition和Direct2D的互操作，直接把Lottie Visual的渲染结果绘制到可读取的D2D Bitmap上：

实现步骤： #

1. 关联CompositionGraphicsDevice与Direct2D设备
   确保用同一个Direct3D设备创建CompositionGraphicsDevice和Direct2D设备，你更新代码里的这一步是正确的。

2. 创建渲染Surface并渲染Lottie Visual
   将Lottie Visual添加到SpriteVisual，再通过CompositionRenderer渲染到DrawingSurface：

   // 创建SpriteVisual并挂载Lottie Visual
   winrt::Windows::UI::Composition::SpriteVisual renderVisual = compositor.CreateSpriteVisual();
   renderVisual.Size({400, 400});
   renderVisual.Children().InsertAtTop(m_visual);
   
   // 创建用于渲染的DrawingSurface
   auto renderSurface = gDevice.CreateDrawingSurface(
       winrt::Windows::Foundation::Size{400, 400},
       winrt::Windows::Graphics::DirectX::DirectXPixelFormat::B8G8R8A8UIntNormalized,
       winrt::Windows::Graphics::DirectX::DirectXAlphaMode::Premultiplied);
   
   // 渲染Visual到Surface
   auto renderer = compositor.CreateRenderer();
   renderer.RenderTarget(renderSurface);
   renderer.Render(renderVisual);
   

3. 从Surface复制像素到可CPU读取的D2D Bitmap
   通过ICompositionDrawingSurfaceInterop获取D2D DeviceContext，将Surface内容复制到指定Bitmap后读取像素：

   auto surfaceInterop = renderSurface.as<ABI::Windows::UI::Composition::ICompositionDrawingSurfaceInterop>();
   CComPtr<ID2D1DeviceContext> dc;
   POINT offset{};
   winrt::check_hresult(surfaceInterop->BeginDraw(nullptr, __uuidof(dc), reinterpret_cast<void**>(&dc), &offset));
   
   // 创建可CPU读取的Bitmap
   D2D1_BITMAP_PROPERTIES1 prop{};
   prop.pixelFormat = D2D1::PixelFormat(DXGI_FORMAT_B8G8R8A8_UNORM, D2D1_ALPHA_MODE_PREMULTIPLIED);
   prop.dpiX = 96;
   prop.dpiY = 96;
   prop.bitmapOptions = D2D1_BITMAP_OPTIONS_CPU_READ | D2D1_BITMAP_OPTIONS_CANNOT_DRAW;
   
   CComPtr<ID2D1Bitmap1> cpuBitmap;
   winrt::check_hresult(dc->CreateBitmap(D2D1::SizeU(400, 400), nullptr, 0, prop, &cpuBitmap));
   
   // 复制Surface内容到Bitmap
   winrt::check_hresult(cpuBitmap->CopyFromRenderTarget(nullptr, dc, nullptr));
   
   // 读取像素数据
   D2D1_MAPPED_RECT mappedRect{};
   winrt::check_hresult(cpuBitmap->Map(D2D1_MAP_OPTIONS_READ, &mappedRect));
   // mappedRect.pBits即为像素数据
   cpuBitmap->Unmap();
   
   winrt::check_hresult(surfaceInterop->EndDraw());
   

关键注意事项 #

• 所有Composition对象（Compositor、Visuals、Target）的生命周期必须和DispatcherQueue绑定，DispatcherQueueController不能提前销毁。
• Direct3D设备需支持至少Feature Level 11.0，且创建时要开启D3D11_CREATE_DEVICE_BGRA_SUPPORT标志。
• 确保DispatcherQueue的消息循环正常运行，否则Lottie的Progress动画无法更新。

内容的提问来源于stack exchange，提问作者Nikolay