c++ - 如何填充常量着色器以避免 E_INVALIDARG？

Question

我正在调查一个 E_INVALIDARG 异常，当我尝试创建第二个常量缓冲区来存储我的灯光信息时抛出该异常:

    // create matrix stack early
    CD3D11_BUFFER_DESC constantMatrixBufferDesc(sizeof(ModelViewProjectionConstantBuffer), D3D11_BIND_CONSTANT_BUFFER);
    DX::ThrowIfFailed(
        m_d3dDevice->CreateBuffer(
        &constantMatrixBufferDesc,
        nullptr,
        &m_constantMatrixBuffer
        )
        );

    DX::ThrowIfFailed(
        m_matrixStack.Initialize(m_d3dContext, m_constantMatrixBuffer, &m_constantMatrixBufferData)
        );

    // also create the light buffer early, we must create it now but we will later
    // update it with the light information that we parsed from the model
    CD3D11_BUFFER_DESC constantLightBufferDesc(sizeof(LightConstantBuffer), D3D11_BIND_CONSTANT_BUFFER);

/* !!!!---- AN E_INVALIDARG IS THROWN BY THE FOLLOWING LINE ----!!!! */
    DX::ThrowIfFailed(
        m_d3dDevice->CreateBuffer(
        &constantLightBufferDesc,
        nullptr,
        &m_constantLightBuffer
        )
        );

此时，似乎传递到 Light 的 CreateBuffer 调用的参数与 Matrix 的状态相同!问题似乎与缓冲区描述中存储的字节数有关。

缓冲区在模块中是这样定义的:

// a constant buffer that contains the 3 matrices needed to
// transform points so that they're rendered correctly
struct ModelViewProjectionConstantBuffer
{
    DirectX::XMFLOAT4X4 model;
    DirectX::XMFLOAT4X4 view; 
    DirectX::XMFLOAT4X4 projection;
};

// a constant buffer that contains up to 4 directional or point lights
struct LightConstantBuffer
{
    DirectX::XMFLOAT3 ambient[4];
    DirectX::XMFLOAT3 diffuse[4];
    DirectX::XMFLOAT3 specular[4];

    // the first spot in the array is the constant attenuation term,
    // the second is the linear term, and the third is quadradic
    DirectX::XMFLOAT3 attenuation[4];

    // the position and direction of the light
    DirectX::XMFLOAT3 position[4];
    DirectX::XMFLOAT3 direction[4];

    // the type of light that we're working with, defined in lights.h
    UINT type[4];

    // a number from 0 to 4 that tells us how many lights there are
    UINT num;
};

因此在顶点着色器 (.hlsl) 中:

cbuffer ModelViewProjectionConstantBuffer : register (b0)
{
    matrix model;
    matrix view;
    matrix projection;
};

cbuffer LightConstantBuffer : register (b1)
{
    float3 ambient[4];
    float3 diffuse[4];
    float3 specular[4];

    // the first spot in the array is the constant attenuation term,
    // the second is the linear term, and the third is quadradic
    float3 attenuation[4];

    // the position and direction of the light
    float3 position[4];
    float3 direction[4];

    // the type of light that we're working with, defined in lights.h
    uint type[4];

    // a number from 0 to 4 that tells us how many lights there are
    uint num;
}

为了找出造成这种情况的原因，我在 MSDN HLSL 着色器文档 (http://msdn.microsoft.com/en-us/library/windows/desktop/ff476898(v=vs.85).aspx) 中偶然发现了这一行:

Each element stores a 1-to-4 component constant, determined by the format of the data stored.

这是什么意思，是这个异常的原因吗？我注意到在 Visual Studio 3D 初学者工具包 ( http://code.msdn.microsoft.com/wpapps/Visual-Studio-3D-Starter-455a15f1 ) 中，缓冲区有额外的 float 填充它们:

///////////////////////////////////////////////////////////////////////////////////////////
    //
    // Constant buffer structures
    //
    // These structs use padding and different data types in places to adhere
    // to the shader constant's alignment.
    //
    struct MaterialConstants
    {
        MaterialConstants()
        {
            Ambient = DirectX::XMFLOAT4(0.0f,0.0f,0.0f,1.0f);
            Diffuse = DirectX::XMFLOAT4(1.0f,1.0f,1.0f,1.0f);
            Specular = DirectX::XMFLOAT4(0.0f, 0.0f, 0.0f, 0.0f);
            Emissive = DirectX::XMFLOAT4(0.0f, 0.0f, 0.0f, 0.0f);
            SpecularPower = 1.0f;
            Padding0 = 0.0f;
            Padding1 = 0.0f;
            Padding2 = 0.0f;
        }

        DirectX::XMFLOAT4   Ambient;
        DirectX::XMFLOAT4   Diffuse;
        DirectX::XMFLOAT4   Specular;
        DirectX::XMFLOAT4   Emissive;
        float               SpecularPower;
        float               Padding0;
        float               Padding1;
        float               Padding2;
    };

    struct LightConstants
    {
        LightConstants()
        {
            ZeroMemory(this, sizeof(LightConstants));
            Ambient = DirectX::XMFLOAT4(1.0f,1.0f,1.0f,1.0f);
        }

        DirectX::XMFLOAT4   Ambient;
        DirectX::XMFLOAT4   LightColor[4];
        DirectX::XMFLOAT4   LightAttenuation[4];
        DirectX::XMFLOAT4   LightDirection[4];
        DirectX::XMFLOAT4   LightSpecularIntensity[4];
        UINT                IsPointLight[4*4];
        UINT                ActiveLights;
        float               Padding0;
        float               Padding1;
        float               Padding2;
    };

    ... // and there's even more where that came from

那么我只是没有正确填充这些东西吗？如果是这样，我应该如何填充它们？还是我缺少的是完全不同的东西？

非常感谢您阅读本文并尝试提供帮助。

Answer 1

由于缺少重要信息，很难解决您的问题，但让我们试一试。

显然，“E_INVALIDARG”表示传递给函数的参数无效。现在我们必须弄清楚哪个参数是错误的。 ID3D11Device::CreateBuffer方法接受 3 个参数:D3D11_BUFFER_DESC , D3D11_SUBRESOURCE_DATA 和 ID3D11Buffer ** 本身。

然后您向它提供 &constantLightBufferDesc、nullptr、&m_constantLightBuffer。现在您必须仔细阅读所有 4 篇 MSDN 文章以找出问题所在。

1. constantLightBuffer 这不是问题，只要检查它是否具有 ID3D11Buffer 指针类型即可。
2. nullptr这不太可能是个问题， 但据我所知，它不是 C++ 标准关键字，所以在这里简单的 '0' 可能会更好。 ^{实际上，它是 C++11 以来的标准}
3. 很遗憾，您没有提供您的 constantLightBufferDesc 定义，这可能会成为一个问题:正如您所说，可能存在缓冲区对齐错误:如果您的 constantLightBufferDesc.BindFlags 具有 D3D11_BIND_CONSTANT_BUFFER 标志和 constantLightBufferDesc.ByteWidth is not a multiple of 16 , 缓冲区创建失败。但这只是一个猜测。您可以在这里有任何其他不匹配，因此，您可以无限地猜测。

幸运的是，还有另一种诊断方法:如果您创建 ID3D11Device与 D3D11_CREATE_DEVICE_DEBUG标志，在 Visual Studio 输出窗口中，您将根据 D3D11 看到所有警告和错误。例如，如果未对齐，您将看到:

D3D11 ERROR: ID3D11Device::CreateBuffer: The Dimensions are invalid. For ConstantBuffers, marked with the D3D11_BIND_CONSTANT_BUFFER BindFlag, the ByteWidth (value = 10) must be a multiple of 16. ByteWidth must also be less than or equal to 65536 on the current driver. [ STATE_CREATION ERROR #66: CREATEBUFFER_INVALIDDIMENSIONS]

因此，如果 CreateBuffer() 由于错误的缓冲区大小而失败，有几种方法可以处理此问题:

1. 调整结构的大小:添加填充成员，使总的 sizeof() 成为 16 的倍数。
2. 将您的结构声明为 16 位对齐。据我所知，只有特定于编译器的方法可以做到这一点:例如 #pragma pack对于 MSVC。
3. 分配给 ByteWidth 的不是实际结构大小，而是四舍五入为 16 的下一个倍数:link

调试愉快! =)