常量缓冲区包含着色器常量数据.本节描述如何在准备渲染时初始化常量缓冲区。

初始化常量缓冲区

1. 定义描述常量数据的结构。
2. 通过填充D3D11_BUFFER_DESC结构创建缓冲区描述，将D3D11_BIND_CONSTANT_BUFFER标志传递给BindFlags成员，并将常量缓冲区描述结构的大小(以字节为单位)传递给ByteWidth成员。注意，D3D11_BIND_CONSTANT_BUFFER标志不能与任何其他标志组合。
3. 调用ID3D11Device::CreateBuffer，同时传递D3D11_BUFFER_DESC结构、D3D11_SUBRESOURCE_DATA结构和指向ID3D11Buffer接口的指针的地址进行初始化。

下面的代码示例演示如何创建常量缓冲区。本例假设g_pd3dDevice是一个有效的ID3D11Device对象，g_pd3dContext是一个有效的ID3D11DeviceContext对象。

ID3D11Buffer*   g_pConstantBuffer11 = NULL;

// Define the constant data used to communicate with shaders.
struct VS_CONSTANT_BUFFER
{
    D3DXMATRIX mWorldViewProj;                              
    D3DXVECTOR4 vSomeVectorThatMayBeNeededByASpecificShader;
    float fSomeFloatThatMayBeNeededByASpecificShader;
    float fTime;                                            
    float fSomeFloatThatMayBeNeededByASpecificShader2;
    float fSomeFloatThatMayBeNeededByASpecificShader3;
};

// Fill in a buffer description.
D3D11_BUFFER_DESC cbDesc;
cbDesc.ByteWidth = sizeof( VS_CONSTANT_BUFFER );
cbDesc.Usage = D3D11_USAGE_DYNAMIC;
cbDesc.BindFlags = D3D11_BIND_CONSTANT_BUFFER;
cbDesc.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
cbDesc.MiscFlags = 0;
cbDesc.StructureByteStride = 0;

// Create the buffer.
hr = g_pd3dDevice->CreateBuffer( &cbDesc, NULL, 
                                 &g_pConstantBuffer11 );

if( FAILED( hr ) )
   return hr;

// Set the buffer.
g_pd3dContext->VSSetConstantBuffers( 0, 1, &g_pConstantBuffer11 );