Visual C++ DirectX11 - Updating Dynamic Resource not working as expected

Question

I want to update the vertices of a DirectX11 ID3D11Buffer, but it is not working. I followed the guide How to use dynamic resources from Microsoft.

This is my code for the buffer:

// Create vertex buffer
int verticesAmount = 5;
pVertices = new XMFLOAT3[verticesAmount];
pVertices[0] = XMFLOAT3( -0.1f, -0.1f, 0 );
pVertices[1] = XMFLOAT3( -0.1f, 0.1f, 0 );
pVertices[2] = XMFLOAT3( 0.1f, 0.1f, 0 );
pVertices[3] = XMFLOAT3( 0.1f, -0.1f, 0 );
pVertices[4] = XMFLOAT3( -0.1f, -0.1f, 0 );

D3D11_BUFFER_DESC bd;
ZeroMemory( &bd, sizeof(bd) );
bd.Usage = D3D11_USAGE_DYNAMIC;
bd.ByteWidth = sizeof( XMFLOAT3 ) * verticesAmount;//sizeof(vertices);
bd.BindFlags = D3D11_BIND_VERTEX_BUFFER;
bd.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
bd.MiscFlags = 0;
bd.StructureByteStride = 0;

D3D11_SUBRESOURCE_DATA InitData;
ZeroMemory( &InitData, sizeof(InitData) );
InitData.pSysMem = pVertices;
InitData.SysMemPitch = 0;
InitData.SysMemSlicePitch = 0;

result = pDevice->CreateBuffer( &bd, &InitData, &pLineStripBuffer )

This is my code when updating:

//pVertices[2].x += 0.1f;  commented because I want to test whether it updates at all
D3D11_MAPPED_SUBRESOURCE mappedResource;
ZeroMemory(&mappedResource, sizeof(D3D11_MAPPED_SUBRESOURCE));
//  Disable GPU access to the vertex buffer data.
pContext->Map(pLineStripBuffer, 0, D3D11_MAP_WRITE_DISCARD, 0, &mappedResource);
//  Update the vertex buffer here.
memcpy(mappedResource.pData, pVertices, 5);
//  Reenable GPU access to the vertex buffer data.
pContext->Unmap(pLineStripBuffer, 0)

This is what it looks like when the update code above is commented out:

This is what is looks like uncommented:

The screenshot of the updated buffer should be the same as the one above because the vertices didn't change positions.

Answer 1

It turned out that the size memcpy was to small. The code in the question only copies the x of the first XMFLOAT3 vector. When I would render the buffer, the first line would go from the center to x of the first vector.

memcpy(mappedResource.pData, pVertices, 5 * sizeof(XMFLOAT3));