The Monolithic D3D11 Runtime

The Monolithic (or Mono) version of the D3D11 runtime provides a high-performance runtime by using streamlined, Xbox-specific versions of DirectX APIs. This version is platform-specific and has the generalized code from D3D11 removed.

Note The Stock version of the Direct3D driver has been removed from the XDK, so now, all development using the XDK is for Monolithic.

• Overview of Monolithic Direct3D
• Header and Library Files for Monolithic
• Flavors of Monolithic
• Monolithic-specific methods
• Shader Resource Views
• Using Deferred Contexts with Monolithic
• DXGI Formats: Monolithic Provides Additional Support for 16-bit Depth Buffers
• Additional Swap Chain Flags in Monolithic
• Monolithic Can Use Alpha Blend Without Dithering
• Gamma Ramp
• Monolithic APIs and COM
• Resources

Overview of Monolithic Direct3D

Many of the changes to Direct3D from the Windows version are because Xbox One uses a single specific hardware platform, and Game OS titles require very high graphics performance. Because the target hardware is specific rather than having to support a variety of CPUs and GPUs, a layer of abstraction has been removed to provide faster performance.

The Monolithic runtime is required for all titles. There is a single driver that combines the Direct3D runtime and user-mode driver, removing unnecessary abstraction and improving performance.

Monolithic Direct3D is encapsulated in the unified header file d3d11_x.h, which incorporates relevant definitions, types, and interfaces from the following Windows header files:

• d3d11.h, d3d11_1.h, and select d3d10 headers
• d3dcommon.h
• dxgi.h, dxgi1_2.h, dxgiformat.h, and dxgitype.h

The runtime is built to d3d11_x.dll. The d3dcompiler library itself remains an independent entity. All of the samples available at Xbox One Samples use the Monolithic runtime.

Header and Library Files for Monolithic

Flavors of Monolithic

Under Monolithic, the graphics User Mode driver has been split into four new flavors, selected with a set of new D3D11CreateDevice flags:

In addition to these flags, there are some other creation flags that are specific to Monolithic Direct3D (described in the table in Direct3D Creation Flags and Supported Formats on Xbox One).

Monolithic-specific methods

The Monolithic version of Direct3D also includes a number of methods that are not available in Windows DirectX to aid in maximizing performance. These methods have Fast inserted into the method name. There are a number of limitations that apply to the fast versions, described below the table.

The “Fast” methods have the following requirements or limitations:

• Before calling a “Fast” method, the caller must have set the appropriate resource to NULL using the appropriate Windows ID3D11DeviceContext method. For example, to make a call to PSSetFastConstantBuffer on slot 2, first make sure that the last call to PSSetConstantBuffers set that slot to NULL. Do not call PSSetConstantBuffers(NULL) before every call to PSSetFastConstantBuffer(), as that will defeat all the optimizations. Instead, call PSSetConstantBuffers(NULL) on a slot and then do a whole batch of “Fast” calls using that slot.
• The caller is responsible for all synchronization and GPU cache invalidation. The methods ID3D11DeviceContextX::FlushGpuCacheRange and ID3D11DeviceContextX::InsertWaitUntilIdle are provided as basic methods for doing this.
• The “Fast” methods do not accept NULL pointers.
• The “Fast” methods do not accept dynamic resources.
• The ID3D11DeviceContextX::xSSetFastShaderResource methods, such as ID3D11DeviceContextX::PSSetFastShaderResource, cannot take color or depth buffers.
• The ID3D11DeviceContextX::xSSetFastShaderResource methods, such as ID3D11DeviceContextX::PSSetFastShaderResource, cannot take MSAA textures.
• Direct3D does not do any state shadowing. “Get” versions of the methods will not return a pointer, but will return NULL.
• The ID3D11DeviceContextX::xSSetPlacement… methods, such as ID3D11DeviceContextX::PSSetPlacementShaderResource, take a pointer to the beginning of the resource allocation. This is important, for example, if PSSetPlacementShaderResource is called with a shader resource view created from an MIP level; the pointer supplied points to the base.

Shader Resource Views

The D3D11X_SRV_FORMAT structure is used with D3D Monolithic shader resource views. D3D11X_SRV_FORMAT allows the title to change the data format, numeric format, and component swizzle of a shader resource view after creation. The formats and swizzles are specified in their hardware form, which is enumerated in D3D11X_IMG_DATA_FORMAT, D3D11X_IMG_NUM_FORMAT, and D3D11X_SWIZZLE.

The D3D11X_SRV_FORMAT structure is output by ID3D11ShaderResourceView::GetFormatX, and is passed into ID3D11ShaderResourceView::SetFormatX.

Using Deferred Contexts with Monolithic

The following flag can be passed to improve the performance of ID3D11Device::CreateDeferredContext.

DXGI Formats: Monolithic Provides Additional Support for 16-bit Depth Buffers

The Xbox One hardware supports 16-bit depth buffers with 8-bit stencil; in the DXGI_FORMAT enumeration, refer to the following enumeration constants:

• DXGI_FORMAT_D16_UNORM_S8_UINT
• DXGI_FORMAT_R16_UNORM_X8_TYPELESS
• DXGI_FORMAT_X16_TYPELESS_G8_UINT

These formats offer higher performance when a stencil is required but depth precision does not need to be very high for the scene being rendered; for example, with certain shadow maps.

Additional Swap Chain Flags in Monolithic

The following are additional flags that are available in Monolithic Direct3D that are not in Windows DirectX, for DXGI_SWAP_CHAIN_FLAG.

Monolithic Can Use Alpha Blend Without Dithering

There is an option in Monolithic Direct3D to disable dithering, when alpha blend is used. When using Windows Direct3D, if alpha blend is used, dithering cannot be turned off.

When using Monolithic, to control whether dithering is enabled, in the D3D11_BLEND_DESC1 structure, for the AlphaToCoverageEnable member, specify 0, 1, or 2, as follows:

The choice to enable or disable dithering is purely aesthetic.

Gamma Ramp

There is some support for the Gamma ramp methods of the IDXGIOutput interface. An IDXGIOutput interface represents an adapter output, such as a monitor. The three supported methods work like the Windows equivalents, except that they are supported on Xbox One in either display mode (Full screen or Snapped).

Monolithic APIs and COM

The Monolithic APIs use a Microsoft COM-like architecture, but they do not actually use COM. Addref and Release work, but nothing beyond that is guaranteed to work. Monolithic interfaces may be wrapped in the Microsoft::WRL::ComPtr class and most functionality will work as expected. However, there is a case where calling QueryInterface on a Monolithic interface wrapped in a ComPtr class results in a compiler error. This behavior is “by design” because the Monolithic APIs do not provide a full implementation of COM.

The following code will give a compiler error (QueryInterface’ : cannot access private member declared in class):

      Microsoft::WRL::ComPtr<ID3D11DeviceContextX>  m_pd3dContextX;
      Microsoft::WRL::ComPtr<ID3D11DeviceContext>   m_pd3dContext;

      // TODO: ....create context for m_pd3dContext as usual.

      // Call QueryInterface to get the ID3D11DeviceContextX
      m_pd3dContext->QueryInterface(__uuidof(ID3D11DeviceContextX), (VOID**)&m_pd3dContextX);  

The way to get around this is to call QueryInterface on the actual context pointer and not the wrapped smart pointer. Replace the last line in the code above with:

      m_pd3dContext.Get()->QueryInterface(__uuidof(ID3D11DeviceContextX), (VOID**)&m_pd3dContextX);  

Note the use of the Get method on the COM pointer, which performs the operation on the underlying pointer directly.

In general, to create Monolithic D3D devices and contexts use ID3D11DeviceContextX and ID3D11DeviceX interfaces.

Resources

See the following white papers:

• Xbox One Graphics Driver Architecture (Developer Education Materials > All NDA Whitepapers)
• D3D Monolithic Runtime and APIs (Developer Education Materials > All NDA Whitepapers)

The full list of white papers is available at Xbox Game Developer: White Papers.

See also

DirectX