How to read vertices from vertex buffer in Direct3d11

Question

I have a question regarding vertex buffers. How does one read the vertices from the vertex buffer in D3D11? I want to get a particular vertex\'s position for calculations, i

Answer 1

Drop's answer was helpful. I figured that the reason why I wasn't able to read the buffer was because I didn't have the CPU_ACCESS_FLAG set to D3D11_CPU_ACCESS_READ before. Here

D3D11_BUFFER_DESC bufferDesc;
ZeroMemory(&bufferDesc, sizeof(bufferDesc));
bufferDesc.ByteWidth = iNumElements * sizeof(T);
bufferDesc.Usage = D3D11_USAGE_DEFAULT;
bufferDesc.CPUAccessFlags = D3D11_CPU_ACCESS_READ | D3D11_CPU_ACCESS_WRITE;
bufferDesc.BindFlags = D3D11_BIND_UNORDERED_ACCESS | D3D11_BIND_SHADER_RESOURCE ;
bufferDesc.MiscFlags = D3D11_RESOURCE_MISC_BUFFER_STRUCTURED;
bufferDesc.StructureByteStride = sizeof(T);

And then to read data I did

    const ID3D11Device& device = *DXUTGetD3D11Device();
    ID3D11DeviceContext& deviceContext = *DXUTGetD3D11DeviceContext();
    D3D11_MAPPED_SUBRESOURCE ms;
    HRESULT hr = deviceContext.Map(g_pParticles, 0, D3D11_MAP_READ, 0, &ms);    

    Particle* p = (Particle*)malloc(sizeof(Particle*) * g_iNumParticles);
    ZeroMemory(p, sizeof(Particle*) * g_iNumParticles);
    memccpy(p, ms.pData, 0, sizeof(ms.pData));
    deviceContext.Unmap(g_pParticles, 0);

    delete[] p;

I agree it's a performance decline, I wanted to do this, just to be able to debug the values!

Thanks anyway! =)