Updates for IddCx versions 1.6 and later

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The following updates in IddCx version 1.6 apply to both console and remote indirect display drivers (IDDs).

The release prior to IddCx version 1.6 was version 1.4. IddCx version 1.5 contains internal changes only that do not affect external indirect display drivers (IDDs). For more information about version 1.4, see IddCx 1.4 updates.

Updated IddCxGetVersion version

The IddCx version returned by IddCxGetVersion on Windows 10, version 20H2 was updated to IDDCX_VERSION_MANGANESE (0x1600). See IddCx versions for a complete list of IddCx-related version information.

WPP information in public IddCx symbols

Starting with IddCx version 1.6, the public IddCx symbol files contain all the Windows software trace processor (WPP) information. This means that the !wmitrace.logdump debugger command decodes and displays the WPP message in the kernel debugger.

Ability to access buffers allocated in system memory

In certain scenarios, swapchain buffers are resident in system memory; for example, when the render adapter being used is WARP (Windows Advanced Rasterization Platform, the system-supplied software renderer). IddCx 1.6 adds the following OS callbacks that allow the driver to access buffers in system memory thus avoiding a sub-resource copy:

  • IddCxSwapChainInSystemMemory allows an IDD to check whether the buffers for a swapchain are resident in system memory. The result of this callback remains constant throughout the lifetime of the swapchain. The driver should check the value of this callback in itsEvtIddCxMonitorAssignSwapChain callback and set up state to release and acquire buffers.

  • IddCxSwapChainReleaseAndAcquireSystemBuffer allows an IDD to release and acquire a buffer, as well as obtain information for accessing the buffer (such as a system memory pointer, pitch/stride of the buffer, surface format and dimensions). The returned buffer is valid until the next successful call to this function.

    At the point of assignment of a new swapchain, the driver must decide which variant of IddCxSwapChainReleaseAndAcquireBuffer/IddCxSwapChainReleaseAndAcquireSystemBuffer it will call for the particular swapchain and must continue using that variant for the rest of lifetime of that swapchain. To decide, the driver should consider its specific requirements and the result of the call to IddCxSwapChainInSystemMemory. A driver will cause the operating system to bugcheck the UMDF process if it:

    • Calls the other variant of IddCxSwapChainReleaseAndAcquireSystemBuffer/IddCxSwapChainReleaseAndAcquireBuffer.
    • Calls IddCxSwapChainReleaseAndAcquireSystemBuffer when IddCxSwapChainInSystemMemory returns false.

It is recommended but not required that a driver use these callback functions. The behavior prior to IddCx 1.6 remains supported.

Ability to access buffers in physically contiguous memory

Starting with IddCx 1.6, the IDDCX_ADAPTER_FLAGS_PREFER_PHYSICALLY_CONTIGUOUS flag and IddCxSwapChainGetPhysicallyContiguousAddress OS callback function were added so that buffers can be accessed in physically contiguous memory.

Display drivers can request that primary surfaces be allocated in physically contiguous system memory by setting the IDDCX_ADAPTER_FLAGS_PREFER_PHYSICALLY_CONTIGUOUS flag in IDDCX_ADAPTER_CAPS. This allows a driver to directly scan out a surface without an intermediate copy.

The driver's request during initialization is not guaranteed to succeed. If the request does not succeed, the call to IddCxAdapterInitAsync will not fail. Instead, once the driver has performed a IddCxSwapChainReleaseAndAcquireBuffer (or IddCxSwapChainReleaseAndAcquireSystemBuffer), it should call IddCxSwapChainGetPhysicallyContiguousAddress to retrieve the physical address of the surface. IddCxSwapChainGetPhysicallyContiguousAddress will first wait for any pending render commands, then flush and invalidate the CPU caches associated with the address range where the surface is stored. However, if the initial request for the surfaces to be allocated in physically contiguous memory failed then IddCxSwapChainGetPhysicallyContiguousAddress will return E_NOINTERFACE.