VBReader

DirectXMesh

This C++ class is used to read elements from vertex buffer(s) based on a Direct3D input layout description. Data is extracted by individual semantics (i.e. POSITION or NORMALS).

This class supports multi-stream vertex buffer descriptions, but does not support instancing vertex buffers.

Header

#include "DirectXMesh.h"

By default, the library supports Direct3D 11. If you want to support Direct3D 12, then you need to #include <d3d12.h> before you do #include "DirectXMesh.h".

Initialization

The reader is initialized by providing a input layout description for the vertex buffer data, and then one or more memory buffers for the input streams.

auto reader = std::make_unique<VBReader>();

D3D11_INPUT_ELEMENT_DESC layout[] =
{
    { "POSITION", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, 0, D3D11_INPUT_PER_VERTEX_DATA, 0 },
    { "TEXCOORD", 0, DXGI_FORMAT_R32G32_FLOAT, 0, 12, D3D11_INPUT_PER_VERTEX_DATA, 0 },
};

struct Vertex
{
    XMFLOAT3 Pos;
    XMFLOAT2 Tex;
};

if ( FAILED( reader->Initialize( layout, 2 ) ) )
   // Error

// For Direct3D 12, use:
//    D3D12_INPUT_LAYOUT_DESC desc = { layout, 2 };
//    if ( FAILED( reader->Initialize( desc ) ) )

if ( FAILED( reader->AddStream( vbdata, nVerts, 0, sizeof(Vertex) ) ) )
   // Error

Note that AddStream can accept a stride of 0 which means to use the stride implied by the input layout description.

Extracting vertex data

The reader is designed to extract an array of XMVECTOR values given the layout semantic name and semantic index.

struct aligned_deleter { void operator()(void* p) { _aligned_free(p); } };

std::unique_ptr<XMVECTOR[], aligned_deleter> buff(
    reinterpret_cast<XMVECTOR*>( _aligned_malloc( sizeof(XMVECTOR) * nVerts, 16 ) ) );

if ( FAILED( reader->Read( buff.get(), "POSITION", 0, nVerts ) ) )
   // Error

// Load position data from XMVECTOR buff array

To simplify implementation of applications, the reader will accept either POSITION or SV_Position as an alias for the actual semantic name provided in the layout.

Biased data

The Read method takes an optional bool x2bias that defaults to false. If set to true, then DXGI_FORMAT_x_UNORM and DXGI_FORMAT_R11G11B10_FLOAT values are scaled so that the 0 to 1 range becomes -1 to 1. Typically this is used to store normals in compressed formats such as DXGI_FORMAT_R10G10B10A2_UNORM.