DirectX - Buffers

For the GPU to access an array of vertices, they need to be placed in a special resource structure called a buffer, which is represented by the ID3D11Buffer interface.

A buffer that stores vertices is called a vertex buffer. Direct3D buffers not only store data, but also describe how the data will be accessed and where it will be bound to the rendering pipeline.

Indices and Index Buffers

Because indices need to be accessed by the GPU, they need to be placed in a special resource structure — an index buffer. Creating an index buffer is very similar to creating a vertex buffer, except that the index buffer stores indices instead of vertices. Therefore, rather than repeating a discussion similar to the one carried out for vertex buffers, we just show an example of creating an index buffer −

UINT indices[24] = {
   0, 1, 2, // Triangle 0
   0, 2, 3, // Triangle 1
   0, 3, 4, // Triangle 2
   0, 4, 5, // Triangle 3
   0, 5, 6, // Triangle 4
   0, 6, 7, // Triangle 5
   0, 7, 8, // Triangle 6
   0, 8, 1 // Triangle 7
};
// Describe the index buffer we are going to create. Observe the
// D3D11_BIND_INDEX_BUFFER bind flag
D3D11_BUFFER_DESC ibd;
ibd.Usage = D3D11_USAGE_IMMUTABLE;
ibd.ByteWidth = sizeof(UINT) * 24;
ibd.BindFlags = D3D11_BIND_INDEX_BUFFER;
ibd.CPUAccessFlags = 0;
ibd.MiscFlags = 0;
ibd.StructureByteStride = 0;
// Specify the data to initialize the index buffer.
D3D11_SUBRESOURCE_DATA iinitData;
iinitData.pSysMem = indices;
// Create the index buffer.
ID3D11Buffer* mIB;
HR(md3dDevice->CreateBuffer(&ibd, &iinitData, &mIB));

As with vertex buffers, and other Direct3D resources for that matter, before we can use it, we need to bind it to the pipeline. An index buffer is bound to the input assembler stage with theID3D11DeviceContext::IASetIndexBuffer method.

Following is an example call −

md3dImmediateContext->IASetIndexBuffer(mIB, DXGI_FORMAT_R32_UINT, 0);
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