为什么 Direct3D 11 中的顶点输入参数使用 DXGI 格式

Question

I was learning Direct3D 11 sometime ago, I switched from DX9 to DX11 because it has more features. But, I can't explain why input vertex layout format use DXGI formats like this

polygonLayout.Format = DXGI_FORMAT_R32G32B32_FLOAT; //For position i don't need color

In Direct3D9 it was simpler using D3DVERTEXELEMENT9:

D3DVERTEXELEMENT9 dwDecl3[] = 
{
    {0, 0,  D3DDECLTYPE_FLOAT3,   D3DDECLMETHOD_DEFAULT, 
                                      D3DDECLUSAGE_POSITION, 0},
    {0, 12, D3DDECLTYPE_D3DCOLOR, D3DDECLMETHOD_DEFAULT, 
                                      D3DDECLUSAGE_COLOR, 0},
    {0, 16, D3DDECLTYPE_D3DCOLOR, D3DDECLMETHOD_DEFAULT, 
                                      D3DDECLUSAGE_COLOR, 1},
    {1,  0, D3DDECLTYPE_FLOAT2,   D3DDECLMETHOD_DEFAULT, 
                                      D3DDECLUSAGE_TEXCOORD, 0},
    {2,  0, D3DDECLTYPE_FLOAT2,   D3DDECLMETHOD_DEFAULT, 
                                      D3DDECLUSAGE_TEXCOORD, 1},
    D3DDECL_END()
};

Answer 1

This isn't really a technical or programming question and more of a "why did they do that?" history question.

So...

The original idea was that when Microsoft changed Direct3D 7 to Direct3D 8 to Direct3D 9, the device/adapter enumeration code was always changing even though it all did the same thing. Therefore, the idea of extracting out the bits of the Direct3D API that did device/adapter enumeration was hit upon and thus DirectX Graphics Infrastructure (DXGI) was created to address this need. Hence why enumerations like pixel formats are in DXGI_FORMAT_* enums rather than "Direct3D enums".

The plan at the time was that DXGI wouldn't need to change and that you could just write this stuff once and it would work for Direct3D 10 and future versions of DirectX.

Alas, "no plan survives contact with the enemy" and DXGI has changed almost constantly with every change of Direct3D and Windows OS.

DXGI 1.0      Windows Vista and Direct3D 10

DXGI 1.1      Windows 7 and Direct3D 11
              The "you really need to use DXGICreateFactory1" release
              Included BGR formats for D3D_FEATURE_LEVEL_9_x devices
              Included BC6/BC7 formats for D3D_FEATURE_LEVEL_11_0 devices

DXGI 1.2      Windows 8 and DirectX 11.1
              Windows Store apps and the "CoreWindow" swapchain
              Introduced the DXGI_SWAP_EFFECT_FLIP_SEQUENTIAL flip model
              Included a bunch of new formats for DirectX 11 Video APIs
              Added 16bpp (5:5:5:1, 5:6:5, and 4:4:4:4) formats

DXGI 1.3      Windows 8.1 and DirectX 11.2
              Added DXGICreateFactory2 so you could enable DXGI Debugging

DXGI 1.4      Windows 10 and DirectX 11.3 / 12.0
              Introduced the DXGI_SWAP_EFFECT_FLIP_DISCARD flip model
              DirectX 12 requires  DXGI_SWAP_EFFECT_FLIP_* flip models
              Includes a few more video formats for JPEG hardware decoding support

DXGI 1.5      Windows 10 (15086) added DuplicateOutput1
              Support for Variable refresh rate displays
              (a.k.a. DXGI_PRESENT_ALLOW_TEARING)

DXGI 1.6      Windows 10 (15063) added support for HDR displays

              Windows 10 (16299) added support for some special adapter fences

              Windows 10 (17134) added the DXGI_GPU_PREFERENCE enumeration;
              Also added HDR10+ metadata support

              Windows 10 (17763) added a way to register for an event
              for adapter changes

See DirectX Graphics Infrastructure (DXGI): Best Practices , DXGI Debug Device , and For best performance, use DXGI flip model