Map

HRESULT Map(
    UINT Subresource,
    const D3D12_RANGE  pReadRange,
    void  ppData
)

// Copy the triangle data to the vertex buffer.
UINT8* pVertexDataBegin;
CD3DX12_RANGE readRange(0, 0);        // We do not intend to read from this resource on the CPU.
ThrowIfFailed(m_vertexBuffer->Map(0, &readRange, reinterpret_cast<void**>(&pVertexDataBegin)));
memcpy(pVertexDataBegin, triangleVertices, sizeof(triangleVertices));
m_vertexBuffer->Unmap(0, nullptr);

// Create an upload heap for the constant buffers.
ThrowIfFailed(pDevice->CreateCommittedResource(
&CD3DX12_HEAP_PROPERTIES(D3D12_HEAP_TYPE_UPLOAD),
D3D12_HEAP_FLAG_NONE,
&CD3DX12_RESOURCE_DESC::Buffer(sizeof(ConstantBuffer) * m_cityRowCount * m_cityColumnCount),
D3D12_RESOURCE_STATE_GENERIC_READ,
nullptr,
IID_PPV_ARGS(&m_cbvUploadHeap)));

// Map the constant buffers. Note that unlike D3D11, the resource
// does not need to be unmapped for use by the GPU. In this sample,
// the resource stays 'permanently' mapped to avoid overhead with
// mapping/unmapping each frame.
CD3DX12_RANGE readRange(0, 0);        // We do not intend to read from this resource on the CPU.
ThrowIfFailed(m_cbvUploadHeap->Map(0, &readRange, reinterpret_cast<void**>(&m_pConstantBuffers)));