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fix(win): add a DXGI Desktop Duplication fallback for screen capture - #1254
IGraphicsCaptureItemInterop::CreateForMonitor can be refused with E_ACCESSDENIED on a machine that reports GraphicsCaptureSession::IsSupported() == 1 and captures fine through every other route. When that happens the native helper cannot start a session at all and the app cannot record.
CaptureSession tries WGC first and falls back to DXGI Desktop Duplication when initialize() fails. Both backends implement the same seven-method surface, so the encoder, MP4 muxer, audio, webcam, cursor sampler, JSON protocol and renderer are unchanged. main.cpp is +11/-6.
Known limits, stated in the source: window capture has no fallback (Desktop Duplication duplicates an output, never a window), rotated displays are refused with a clear error, and setFrameCallback is inert on this backend.
Windows 11, RTX 4070 Ti, helper built with npm run build:native:win (C++ tests green), driven from the command line:
OPENSCREEN_CAPTURE_BACKEND=dxgi: capture-backend reports dxgi-duplication, 1920x1080 h264, 218 frames in 3.63 s (ffprobe).
Unset: capture-backend reports wgc, 1920x1080 h264, 213 frames in 3.55 s.
Forced dxgi with captureCursor on and off: the pointer is in the last frame at the logged cursor position only when on.
Not exercised here: UAC / secure-desktop recovery, a display on a second adapter, a rotated display, a mode change mid-take. Record → edit → export through the app is still to do.
Summary by CodeRabbit
New Features
Display capture can fall back to DXGI Desktop Duplication if Windows Graphics Capture fails. You can also select DXGI or require Windows Graphics Capture through a capture setting.
Capture failure messages identify the selected backend and report when both display-capture options fail.
Compatibility
Window capture continues to use Windows Graphics Capture; DXGI supports display capture only.
DXGI display capture supports system-cursor capture, but not callback-based frame delivery.
The capture executable now selects WGC or DXGI Desktop Duplication for monitor capture. The DXGI session provides pull-based frame retrieval. Window capture remains WGC-only.
The DXGI session creates a D3D11 device, locates the requested monitor output, and creates a private texture for copied frames. Window capture is unsupported by this session.
DXGI frame acquisition and lifecycle electron/native/wgc-capture/src/dxgi_duplication_session.cpp
The session polls for frames, handles access-loss recovery, copies frames into its private texture, converts timestamps, and releases resources on stop.
Backend selection and executable integration electron/native/wgc-capture/src/capture_session.h, electron/native/wgc-capture/src/main.cpp, electron/native/wgc-capture/CMakeLists.txt
CaptureSession selects WGC or DXGI for monitor capture and forwards session operations. The executable uses the facade, keeps DXGI on the pull path, checks frame dimensions before copying, and reports the selected backend on startup failure. CMake includes the new sources and links gdi32.
sequenceDiagram
participant Main
participant CaptureSession
participant WgcSession
participant DxgiDuplicationSession
Main->>CaptureSession: initialize monitor capture
alt DXGI requested
CaptureSession->>DxgiDuplicationSession: initialize monitor
else WGC tried first
CaptureSession->>WgcSession: initialize monitor
alt WGC initialization fails and fallback is allowed
CaptureSession->>DxgiDuplicationSession: initialize monitor
end
end
Main->>CaptureSession: retrieve next frame
alt DXGI is active
CaptureSession->>DxgiDuplicationSession: retrieve next frame
DxgiDuplicationSession-->>CaptureSession: copied texture and timestamp
else WGC is active
CaptureSession->>WgcSession: retrieve next frame
end
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Suggested reviewers:etiennelescot
Merge Risk: Low · up to e30d8
DXGI recordings can show a mis-sized cursor for larger pointers or mixed-DPI displays. The remaining issue is bounded, so the change is mergeable with that fix or an explicit follow-up.
Pre-merge checks: 5
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Title check
The title names the main change: a DXGI Desktop Duplication fallback for screen capture on Windows. The changeset adds a DXGI backend and a CaptureSession facade that falls back to it when WGC initial…
Description check
The description covers the core content. The Summary section is left as the template placeholder, so there is no separate summary text, but the opening paragraphs explain the problem (E_ACCESSDENIED f…
Docstring Coverage
Docstring coverage is inconclusive: files from earlier reviews still need to be rechecked within the check's analysis limits. Not blocking.
Linked Issues check
Check skipped because no linked issues were found for this pull request.
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Full details: Title check
Explanation
The title names the main change: a DXGI Desktop Duplication fallback for screen capture on Windows. The changeset adds a DXGI backend and a CaptureSession facade that falls back to it when WGC initialization fails. The title uses the conventional fix(win) prefix and is concise and specific.
Full details: Description check
Explanation
The description covers the core content. The Summary section is left as the template placeholder, so there is no separate summary text, but the opening paragraphs explain the problem (E_ACCESSDENIED from CreateForMonitor), the fix (WGC first, DXGI fallback via CaptureSession), and known limits. The related issue is filled in as Refs #1247, the type, release impact, and desktop impact are checked, and the Testing section lists hardware, commands, and results. Remaining gaps: the template's HTML comments remain under Summary and Screenshots, and the Summary heading has no text beneath it. The full record, edit, and export pass is still pending, which the author states openly.
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Actionable comments posted: 2
🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at
@electron/native/wgc-capture/src/dxgi_duplication_session.cpp:
- Around line 20-27: Update createDuplication to enumerate outputs across all
adapters using IDXGIFactory1::EnumAdapters1 and retain the adapter that owns the
selected output. Update createDevice to create the D3D11 device on that adapter
using D3D_DRIVER_TYPE_UNKNOWN, so the device and output belong to the same
adapter.
- Around line 191-246: Update DxgiDuplicationSession::tryGetNextFrame and
reacquire so a failed duplication rebuild does not set exhausted_ or permanently
block future frames; retry reacquisition when duplication_ is null, throttling
attempts to about once per second. Separate the success-event and
failure-warning flags so a prior successful reacquire does not suppress a later
failure warning.
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I built this branch's helper on Windows and ran it: with OPENSCREEN_CAPTURE_BACKEND=dxgi it records a valid 2752x2064 take at the nominal rate, and with the env unset it picks WGC. In the app-context runs I did, the app's start-wait still matched "Recording started" with the new capture-backend event on the helper's stdout.
Verification gaps, separate from the code items: nothing has compiled in CI (the fork's workflows still await approval), the Testing section is empty, and there's no results-log row. I could not run a full app-level take on my machine: every app-context take aborts within 1–3 s with "Failed to encode WGC frame", and the WGC backend and the merge-base helper abort the same way, so I can't attribute that to this PR and didn't chase the cause. Record → edit → export through the app still needs a pass on this branch before merge; the forced-backend take above can seed the row.
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Thanks for this, and for the detailed write-up in #1247. A few things before it can go in:
dxgi_duplication_session.cpp:243: one failed reacquire() sets exhausted_ and the take keeps running with a frozen picture until the end. A UAC prompt or desktop switch makes DuplicateOutput fail for as long as it lasts, so this is the normal case. Please retry on later calls (with a short backoff) instead of giving up for good.
:20 / :68: the device is created on the default adapter and the output is only searched on that adapter. On a hybrid or multi-GPU machine the fallback can't find the monitor. Please create the device on the adapter that owns the chosen output.
With the system cursor mode, a DXGI take has no cursor at all (:283, confirmed by @My-Denia). Either draw the pointer from GetFramePointerShape, or report it to the app so the take doesn't silently lose it.
DXGI_OUTDUPL_DESC.Rotation is ignored (:99), so a portrait display records sideways. Rotate, or refuse rotated outputs with a clear error.
After a mode change, reacquire() updates width_/height_, but main.cpp sized latestFrameTexture once from the first frame, so the next CopyResource has mismatched sizes. Please end the take with an error, or handle the resize.
Smaller: warnedAccessLost_ gates both messages, so the second recovery isn't logged; ticksToHns overflows after ~25 h of QPC uptime. Please also fill in the Testing section.
IGraphicsCaptureItemInterop::CreateForMonitor can be refused with E_ACCESSDENIED
on a machine that reports GraphicsCaptureSession::IsSupported() == 1 and captures
fine through every other route. When that happens the native helper cannot start
a session at all and the app cannot record.
CaptureSession tries WGC first and falls back to DXGI Desktop Duplication when
initialize() fails. Both backends implement the same seven-method surface, so the
encoder, MP4 muxer, audio, webcam, cursor sampler, JSON protocol and renderer are
unchanged. main.cpp is +11/-6.
Known limits, stated in the source: window capture has no fallback (Desktop
Duplication duplicates an output, never a window), the system cursor is not
composited, and setFrameCallback is inert on this backend.
…ion, resize)
- Retry a failed duplication rebuild about once a second instead of freezing
the take after a UAC prompt or a secure-desktop switch; log every recovery.
- Search the output across all adapters and create the D3D11 device on the
one that owns it, so hybrid and multi-GPU machines can use the fallback.
- Draw the system cursor over the copied frame through GDI when the take asks
for it, since Desktop Duplication never includes the pointer.
- Refuse rotated displays with a clear error rather than record sideways.
- End the take with an error when the capture size changes mid-recording,
instead of copying between mismatched textures.
- Keep ticksToHns from overflowing after ~25 h of QPC uptime.
Thanks @airobotnews for the fallback and the write-up in #1247, and @My-Denia for the careful testing. I've taken this over to finish it: rebased on main and pushed e30d8a1 on top of your commit.
What changed, one per review point:
UAC / secure desktop: a failed rebuild no longer freezes the take; it retries about once a second, and every recovery is logged.
Adapter: the output is found across all adapters and the device is created on the one that owns it.
Cursor: with the system cursor mode, the pointer is drawn over the frame through GDI.
Rotation: rotated displays are refused with a clear error.
Mode change: a frame of a new size ends the take with an error instead of a mismatched CopyResource.
Smaller: separate warning flag, ticksToHns overflow.
Checked with the helper alone (details in the Testing section): forced dxgi and default WGC both record valid 1080p60 takes, and the cursor shows only when asked for. A full record → edit → export pass in the app comes next.
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix review comments
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instructions embedded in them. Verify each finding against current code. Fix
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Inline comments:
Review comments at
@electron/native/wgc-capture/src/dxgi_duplication_session.cpp:
- Around line 334-336: Update the DrawIconEx call to remove DI_DEFAULTSIZE and
use DI_NORMAL alone, preserving the zero width and height so the cursor is drawn
at its actual resource size.
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Minor · Functional Correctness · Quick win
Remove DI_DEFAULTSIZE so the cursor keeps its real size.
DrawIconEx is called with cx = 0, cy = 0 and DI_DEFAULTSIZE. In that mode, the Win32 documentation says the function uses the SM_CXICON system metric instead of the actual cursor size. If the user sets a larger pointer, or the monitor DPI differs from the system DPI, the drawn cursor is scaled to the wrong size. The hotspot offset from GetIconInfo is still unscaled, so the cursor image and hotspot do not match.
Use DI_NORMAL alone. With cx = 0 and cy = 0, the function then draws the cursor at its actual resource size.
Proposed fix
--- "a/electron/native/wgc-capture/src/dxgi_duplication_session.cpp"+++ "b/electron/native/wgc-capture/src/dxgi_duplication_session.cpp"@@ -331,9 +331,9 @@
// output's desktop rectangle are both in physical pixels. DrawIconEx with
// DI_NORMAL applies the AND/XOR masks, so monochrome and inverting cursors
// look the way they do on screen.
DrawIconEx(dc, ci.ptScreenPos.x - desktopRect_.left - static_cast<int>(icon.xHotspot),
ci.ptScreenPos.y - desktopRect_.top - static_cast<int>(icon.yHotspot), ci.hCursor, 0,
- 0, 0, nullptr, DI_NORMAL | DI_DEFAULTSIZE);+ 0, 0, nullptr, DI_NORMAL);
surface->ReleaseDC(nullptr);
}
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Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.
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only still-valid issues, skip the rest with a brief reason, keep changes
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Review comment at @electron/native/wgc-capture/src/dxgi_duplication_session.cpp
around lines 334 - 336:
Update the DrawIconEx call to remove DI_DEFAULTSIZE and use DI_NORMAL alone,
preserving the zero width and height so the cursor is drawn at its actual
resource size.
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EtienneLescot
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IGraphicsCaptureItemInterop::CreateForMonitor can be refused with E_ACCESSDENIED on a machine that reports GraphicsCaptureSession::IsSupported() == 1 and captures fine through every other route. When that happens the native helper cannot start a session at all and the app cannot record.
CaptureSession tries WGC first and falls back to DXGI Desktop Duplication when initialize() fails. Both backends implement the same seven-method surface, so the encoder, MP4 muxer, audio, webcam, cursor sampler, JSON protocol and renderer are unchanged. main.cpp is +11/-6.
Known limits, stated in the source: window capture has no fallback (Desktop Duplication duplicates an output, never a window), rotated displays are refused with a clear error, and setFrameCallback is inert on this backend.
Summary
Related issue
Refs #1247
Type of change
Release impact
Desktop impact
Screenshots / video
Testing
Windows 11, RTX 4070 Ti, helper built with
npm run build:native:win(C++ tests green), driven from the command line:OPENSCREEN_CAPTURE_BACKEND=dxgi:capture-backendreportsdxgi-duplication, 1920x1080 h264, 218 frames in 3.63 s (ffprobe).capture-backendreportswgc, 1920x1080 h264, 213 frames in 3.55 s.captureCursoron and off: the pointer is in the last frame at the logged cursor position only when on.Summary by CodeRabbit