DirectX 11 Map deviceContext failed - visual-studio

Question

I have an application that render a cube and do some other syuff. But unfortunately, when I want to move some vertices with the mouse. I have an error. When I map the vertex buffer, the vertices recorded in another struct array is empty. For testing my application, I just put a map after creating the vertexbuffer in order to see if the debugger show me the real numbers. It fails too. Everything is populated with a 0.00 value (positions, normals, tangents...).What is the problem ?
Here you can find the code.
D3D11_BUFFER_DESC bd;
ZeroMemory( &bd, sizeof(bd) );
bd.Usage = D3D11_USAGE_DYNAMIC; //D3D11_USAGE_DEFAULT; //D3D11_USAGE_DYNAMIC;// D3D11_USAGE_DEFAULT;
bd.ByteWidth = CBSize( sizeof( VERTEX_PNTTB)* NumVertices);
bd.BindFlags = D3D11_BIND_VERTEX_BUFFER;
bd.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE; // 0; // D3D11_CPU_ACCESS_READ; //D3D11_CPU_ACCESS_WRITE; // 0;
bd.StructureByteStride = 0;
bd.MiscFlags = 0;
//bd.StructureByteStride
//bd.MiscFlags = 0;
D3D11_SUBRESOURCE_DATA InitData;
ZeroMemory( &InitData, sizeof(InitData) );
InitData.pSysMem = (void*)vertices; //(void*)(mesh->GetVertexes().data()); //vertices; //(float*)vertices; // (UINT*)vertices;
InitData.SysMemPitch=0;
ID3D11Buffer* vbuff = NULL;
hr = device->CreateBuffer(&bd, &InitData, &vbuff); // &(m->vertexBuffer)); //&m_pVertexBuffer );
//if( FAILED( hr ) )
// return hr;
//}
m->vertexBuffer = vbuff;
D3D11_MAPPED_SUBRESOURCE mappedResource;
ID3D11Buffer* &buff = vbuff;
//g_pImmediateContext->CopyResource(buff, mElements[ 0 ]->getElement().model ->Meshes()[selectedMeshIndex]->VertexBuffer());
hr = g_pImmediateContext->Map( buff, 0, D3D11_MAP_WRITE_DISCARD ,0, &mappedResource); // D3D11_MAP_WRITE_DISCARD, 0, &mappedResource);
if (SUCCEEDED(hr))
{
VERTEX_PNTTB *vertices = (VERTEX_PNTTB *)mappedResource.pData;
// Fill vertex buffer
//vertices[0].position = vertices[0]; // XMFLOAT3(toX0,toY0,0); //-1;//toX0; //-1;//vf1.x; // x0;
/*for(UINT i=0; i<faces_indices.size(); i++)
{
vertices[ faces_indices[i] ].position.x = vertices[faces_indices[i] ].position.x + DirectX::XMFLOAT3(20*dx,20*dy,0).x;
vertices[ faces_indices[i] ].position.y = vertices[faces_indices[i] ].position.y + DirectX::XMFLOAT3(20*dx,20*dy,0).y;
vertices[ faces_indices[i] ].position.z = vertices[faces_indices[i] ].position.z + DirectX::XMFLOAT3(20*dx,20*dy,0).z;
}*/
//g_pImmediateContext->Unmap( mElements[ 0 ]->getElement().model ->Meshes()[selectedMeshIndex]->VertexBuffer(), 0);
g_pImmediateContext->Unmap( buff, 0);
}

Answer 1

Generally you don't want to create Vertex Buffer or Index Buffers in CPU-readable memory as it has a major negative performance impact. You'll find it's much better to have static VB/IB and another copy of the data in standard RAM for the CPU to modify.
That said, you can create the Direct3D 11 buffer in shared memory by using D3D11_USAGE_DYNAMIC and D3D11_CPU_ACCESS_READ | D3D11_CPU_ACCESS_WRITE. You then call Map with D3D11_MAP_READ_WRITE.
You definitely should not use D3D11_MAP_WRITE_DISCARD which gives you a fresh piece of memory that has no data in it which will overwrite the old data when you call Unmap.