DXGI 1.4 Improvements

The following functionality has been added or changed in Microsoft DirectX Graphics Infrastructure (DXGI) 1.4, largely to support Direct3D 12.

Cheaper adapter enumeration

For Direct3D 12, it’s no longer possible to backtrack from a device to the IDXGIAdapter that was used to create it. It’s also no longer possible to provide D3D_DRIVER_TYPE_WARP into D3D12CreateDevice. To make development easier, you can use IDXGIFactory4 to deal with both of these. IDXGIFactory4::EnumAdapterByLuid (designed to be paired with ID3D12Device::GetAdapterLuid) enables an app to retrieve information about the adapter where a Direct3D 12 device was created. IDXGIFactory4::EnumWarpAdapter provides an adapter which can be provided to D3D12CreateDevice to use the WARP renderer.

Video memory budget tracking

Application developers are encouraged to use a video memory reservation system, to inform the OS of the amount of physical video memory the app cannot go without.

The amount of physical memory available for a process is known as the "video memory budget". The budget can fluctuate noticeably as background processes wake-up and sleep; and fluctuate dramatically when the user switches away to another application. The application can be notified when the budget changes and poll both the current budget and the currently consumed amount of memory. If an application doesn’t stay within its budget, the process will be intermittently frozen to allow other applications to run and/or the creation APIs will return failure. The IDXGIAdapter3 interface provides the methods pertaining to this functionality, in particular QueryVideoMemoryInfo and RegisterVideoMemoryBudgetChangeNotificationEvent.

For more information, refer to the Direct3D 12 topic on Residency.

Direct3D 12 Swapchain Changes

Some of the existing Direct3D 11 swapchain functionality was deprecated to achieve the overhead reductions in Direct3D 12. While other changes were made to either align to Direct3D 12 concepts or provide better support for Direct3D 12 features.

Invariant Backbuffer Identity

In Direct3D 11, applications could call GetBuffer( 0, … ) only once. Every call to Present implicitly changed the resource identity of the returned interface. Direct3D 12 no longer supports that implicit resource identity change, due to the CPU overhead required and the flexible resource descriptor design. As a result, the application must manually call GetBuffer for every each buffer created with the swapchain. The application must manually render to the next buffer in the sequence after calling Present. Applications are encouraged to create a cache of descriptors for each buffer, instead of re-creating many objects each Present.

Multi-Adapter Support

When a swapchain is created on a multi-GPU adapter, the backbuffers are all created on node 1 and only a single command queue is supported. ResizeBuffers1 enables applications to create backbuffers on different nodes, allowing a different command queue to be used with each. These capabilities enable Alternate Frame Rendering (AFR) techniques to be used with the swapchain. Refer to Direct3D 12 Multi-Adapters.

Miscellaneous

  • A command queue object must be passed to CreateSwapChain methods instead of the Direct3D 12 device object.
  • Only the following two flip model swap effects are supported:
    DXGI_SWAP_EFFECT_FLIP_DISCARD should be preferred when applications fully render over the backbuffer before presenting it or are interested in supporting multi-adapter scenarios easily.
    DXGI_SWAP_EFFECT_FLIP_SEQUENTIAL should be used by applications that rely on partial presentation optimizations or regularly read from previously presented backbuffers.
  • SetFullscreenState no longer exclusively owns the display, so user-initiated operating system elements can seamlessly appear in front of application output. Volume settings is an example of this.

Direct3D 12 Hardware Feature Levels

Programming Guide for DXGI