Indirect Display

Indirect Display Driver - Quick Reference

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: indirect-display. Authoritative source: learn.microsoft.com/en-us/windows-hardware/drivers/display/indirect-display-driver-model-overview. Canonical sample: general/IddSampleDriver in microsoft/Windows-driver-samples.

What IDD is (and isn't)

IDD is a UMDF v2 driver that registers itself as a display adapter via IddCx. The OS treats the IDD's monitors like real displays for layout, DPI, multi-mon, cursor, etc. The driver receives swap-chains (a stream of GPU surfaces) for each connected monitor and is responsible for consuming the frames somehow.

IDD architecture in one diagram

                Apps (DWM composes the desktop into per-monitor swapchains)
                                           |
   ────────────────────────────── Kernel mode (DXGK / GPU schedulers) ──────────
                                           |   (handled by IddCx + WDDM emulation)
   ────────────────────────────── User mode  (WUDFHost.exe) ────────────────────
                                           |
                            +----------------------------+
                            | Your IDD UMDF DLL          |
                            |  - EvtIddCxAdapterInitFinished
                            |  - EvtIddCxParseMonitorDescription
                            |  - EvtIddCxMonitorGetDefaultModes
                            |  - EvtIddCxMonitorQueryTargetModes
                            |  - EvtIddCxMonitorAssignSwapChain
                            |  - <swap-chain processing thread>
                            |       AcquireBuffer / FinishedProcessing
                            |       -> encode (NVENC) -> send (TCP/UDP/Rivermax)
                            +----------------------------+

Lifecycle / callback flow (simplified)

1. DriverEntry → IddCxDriverInitialize registers IDD
2. EvtDeviceAdd → create the WDF device, then IddCxDeviceInitialize
3. EvtIddCxAdapterInitFinished — adapter is up; you can now plug monitors with IddCxMonitorCreate + IddCxMonitorArrival
4. EvtIddCxParseMonitorDescription / MonitorGetDefaultModes / MonitorQueryTargetModes — declare what the virtual monitor supports (resolution, refresh rate, color)
5. EvtIddCxMonitorAssignSwapChain — DWM is ready to push frames; start your processing thread
6. Processing thread: loop IddCxSwapChainAcquireBuffer → consume → IddCxSwapChainFinishedProcessingFrame → IddCxSwapChainReleaseAndAcquireBuffer
7. EvtIddCxMonitorUnassignSwapChain — stop your thread cleanly
8. Plug-out: IddCxMonitorDeparture → IddCxMonitorReleaseAndDestroy

Monitor descriptor — minimum viable EDID

Provide a synthetic EDID via EvtIddCxParseMonitorDescription. The IDD sample ships an EDID blob; for production, generate one with valid manufacturer ID, product code, supported timings (CEA blocks for HDR/HDMI traits), and checksum.

NTSTATUS MyEvtParseMonitorDescription(
    const IDARG_IN_PARSEMONITORDESCRIPTION* in,
    IDARG_OUT_PARSEMONITORDESCRIPTION*      out)
{
    if (in->MonitorDescription.DataSize != EDID_SIZE) return STATUS_INVALID_PARAMETER;
    // Extract preferred timing from EDID block
    out->MonitorModeBufferOutputCount = 1;
    if (in->pMonitorModes != NULL) {
        in->pMonitorModes[0] = MakeMode(1920, 1080, 60);   // helper builds IDDCX_MONITOR_MODE
    }
    return STATUS_SUCCESS;
}

Swap-chain processing loop (the hot path)

// Started from EvtIddCxMonitorAssignSwapChain
DWORD WINAPI SwapChainProcessor(LPVOID lp) {
    auto* ctx = static_cast<MonitorContext*>(lp);
    auto& dx  = ctx->DxResources;             // your D3D11/D3D12 device + context

    for (;;) {
        IDARG_OUT_RELEASEANDACQUIREBUFFER buf{};
        HRESULT hr = IddCxSwapChainReleaseAndAcquireBuffer(ctx->SwapChain, &buf);
        if (hr == E_PENDING) {
            // Wait on `ctx->NewFrameEvent` with timeout, then continue
            WaitForSingleObject(ctx->NewFrameEvent, 16);   // ~60 fps poll
            continue;
        }
        if (FAILED(hr)) break;                  // shutting down

        // buf.MetaData.PresentationTime, .Buffer (ID3D11Texture2D / DXGI handle)
        // 1. Get the staging texture (or use a shared NT handle)
        // 2. Encode with NVENC / quick-sync / etc.
        // 3. Send the encoded packet over the chosen transport (TCP / UDP / Rivermax)
        ConsumeFrame(ctx, buf);

        IDARG_IN_FINISHEDPROCESSINGFRAME fin{};
        IddCxSwapChainFinishedProcessingFrame(ctx->SwapChain, &fin);
    }
    return 0;
}

The framework hands you GPU surfaces, not CPU bitmaps. Doing CPU-side Map per frame is fast enough for 1080p60 but won't reach 4K60 with low latency — keep the data on the GPU and feed an encoder.

Cursor handling

DWM tells IDD whether the cursor should be drawn into the frame or composited separately. The driver gets cursor shape + position via:

• IddCxMonitorSetupHardwareCursor — opt in to receive a separate cursor surface
• The Cursor event/handle: when signaled, call IddCxMonitorQueryHardwareCursor to get position + new shape

For network streaming, sending the cursor as a separate small surface (vs. baking it into the frame) lets the receiver render it locally for sub-frame latency.

Network streaming patterns

For high resolution / framerate, encode first:

• NVENC (NVIDIA Video Codec SDK): H.264 / HEVC / AV1, very low latency mode; can ingest a D3D11_TEXTURE2D directly with NV_ENC_INPUT_RESOURCE_TYPE_DIRECTX.
• Quick Sync (Intel) via Media Foundation / oneVPL.
• AMF (AMD) for Radeon.
• HEVC over Rivermax SMPTE 2110 / 2022-7 for broadcast-style transport.

Multi-monitor

Call IddCxMonitorArrival once per virtual monitor at startup; the DWM treats each independently. Each gets its own swap-chain assignment + processor thread. Keep per-monitor context small and avoid global state.

HDR (10-bit / scRGB)

Declare HDR capability in the EDID (CEA HDR Static Metadata block) and in IDDCX_MONITOR_MODE.MonitorVideoSignalInfo.ColorInfo. DWM will then push HDR swap-chains (DXGI_FORMAT_R16G16B16A16_FLOAT / R10G10B10A2_UNORM). Your encoder pipeline must support 10-bit HDR (HEVC Main10 / AV1).

INF (UMDF + IddCx)

[Standard.NT$ARCH$.10.0...19041]
%Device.DeviceDesc% = MyIdd_Install, ROOT\MyIddDriver

[MyIdd_Install.NT.Wdf]
UmdfDispatcher       = NativeIdd
UmdfServiceOrder     = MyIddDriver
UmdfDirectHardwareAccess = AllowDirectHardwareAccess
UmdfFileObjectPolicy = AllowNullAndUnknownFileObjects

[MyIddDriver]
UmdfLibraryVersion = $UMDFVERSION$
ServiceBinary      = %13%\MyIddDriver.dll
DriverCLSID        = {GUID}

UmdfDispatcher = NativeIdd is the magic that wires IddCx in.

Anti-Patterns