DirectX12

DirectX12 support in SteamVR

SteamVR supports submission of eye buffers originating from the DirectX12 graphics API.

Image description

When submitting a DirectX12 image as an overlay or eye texture into SteamVR, use TextureType_DirectX12 for its ETextureType. The handle to pass into the Texture_t structure should be a pointer to a D3D12TextureData_t structure containing the DirectX12 resources needed for the runtime to process it:

struct D3D12TextureData_t
{
	ID3D12Resource *m_pResource;
	ID3D12CommandQueue *m_pCommandQueue;
	uint32_t m_nNodeMask;
};

• m_pResource - pointer to ID3D12Resource created with D3D12_RESOURCE_DIMENSION_TEXTURE2D.
• m_pCommandQueue - pointer to ID3D12CommandQueue on which SteamVR will execute the transfer of the image.
• m_nNodeMask - in the case of multi-adapter, this is a bitmask of the set of nodes. If not using multi-adapter, set this to 0.

Image Resource State

The D3D12 m_pResource should be transitioned to the resource state D3D12_RESOURCE_STATE_PIXEL_SHADER_RESOURCE prior to passing it ot the SteamVR runtime. The resource will remain in the D3D12_RESOURCE_STATE_PIXEL_SHADER_RESOURCE state when the submission work has finished executing.

Explicit Timing

Vulkan applications can enable explicit timing mode by calling IVRCompositor::SetExplicitTimingMode. In DirectX12, the purpose of explicit timing mode is to get a more accurate GPU timestamp for when the frame begins.

More accurate GPU timestamp for the start of the frame is achieved by the application calling IVRCompositor::SubmitExplicitTimingData immediately before its first submission to the ID3D12CommandQueue for the frame. This is more accurate because normally this GPU timestamp is recorded during WaitGetPoses. In D3D11, WaitGetPoses queues a GPU timestamp write, but it does not actually get submitted to the GPU until the application performs it next flush. By using SubmitExplicitTimingData, the timestamp is recorded at the same place for DirectX12 as it is for D3D11, resulting in a more accurate GPU time measurement for the frame.

Example Code

An example of using DirectX12 with SteamVR on Windows (Visual Studio 2015+) can be found in the SDK https://github.com/ValveSoftware/openvr/tree/master/samples/hellovr_dx12.