ComPtr.As（）有什么作用？ [英] What does ComPtr.As() do?

问题描述

我正在从一些例子学习DirectX 12，但我无法理解ComPtr.As（）方法是什么。

I am working on learning DirectX 12 from some examples but I am having trouble understanding what does the ComPtr.As() method does.

ComPtr<ID3D12Device> device;
ComPtr<ID3D12Device> device2; 

// Do Stuff with Device
device.As(&device2); // What does this do?

推荐答案

您在哪里找到此示例代码？它看起来鱼腥。这是对 As 的无谓使用。如果你将它扩展到底层的 QueryInterface ：

Where did you find this example code? It looks fishy. This is kind of a nonsense use of As. It's equally silly if you expand it to the underlying QueryInterface:

hr = device->QueryInterface( IID_PPV_ARGS(device2) );

其实，你的代码最好写成：

In fact, your code would be better written as:

device2 = device;

通常你会使用 As 从现有接口的新接口。例如，使用Direct3D 11，您将设备创建为Direct3D 11.0接口，然后必须使用 QueryInterface 11.1，11.2，11.3和/或11.4版本才能使用它们： / p>

Typically you'd use As to obtain a new interface from an existing interface. For example with Direct3D 11, you create the device as a Direct3D 11.0 interface and then have to QueryInterface the 11.1, 11.2, 11.3, and/or 11.4 versions to use them:

ComPtr<ID3D11Device> device;
DX::ThrowIfFailed(D3D11CreateDevice(..., device.ReleaseAndGetAddressOf());

ComPtr<ID3D11Device2> device2;
hr = device.As(&device2);
if (FAILED(hr))
    // Do whatever handling you do if the system doesn't support 11.2

Direct3D 11的另一个常见用途是处理可能不存在的调试界面：

Another common use with Direct3D 11 is dealing with the debug interfaces which may not be present:

#ifndef NDEBUG
    ComPtr<ID3D11Debug> d3dDebug;
    if (SUCCEEDED(device.As(&d3dDebug)))
    {
        ComPtr<ID3D11InfoQueue> d3dInfoQueue;
        if (SUCCEEDED(d3dDebug.As(&d3dInfoQueue)))
        {
#ifdef _DEBUG
            d3dInfoQueue->SetBreakOnSeverity(D3D11_MESSAGE_SEVERITY_CORRUPTION, true);
            d3dInfoQueue->SetBreakOnSeverity(D3D11_MESSAGE_SEVERITY_ERROR, true);
#endif
            D3D11_MESSAGE_ID hide [] =
            {
                D3D11_MESSAGE_ID_SETPRIVATEDATA_CHANGINGPARAMS,
                // TODO: Add more message IDs here as needed.
            };
            D3D11_INFO_QUEUE_FILTER filter = {};
            filter.DenyList.NumIDs = _countof(hide);
            filter.DenyList.pIDList = hide;
            d3dInfoQueue->AddStorageFilterEntries(&filter);
        }
    }
#endif

忽略从 As 返回的HRESULT返回值。您应该使用 SUCCEEDED 或 FAILED 宏或快速失败，例如 ThrowIfFailed 。

It's also important to not ignore the HRESULT return value that comes back from As. You should use SUCCEEDED or FAILED macro, or a fast-fail like ThrowIfFailed.

请参阅 ComPtr 。

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