fix: initialise CoreGraphics before building a macOS window capture filter - #488
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Included review availability: Your plan provides up to 4 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe capture helper initializes CoreGraphics before argument validation and capture setup. The manual E2E checklist records shipped-helper failure and successful branch-built window recording results. ChangesWindow capture initialization
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: 🔵 Low · up to The macOS window-capture fix restores recording for a previously failing path and is supported by successful manual validation. The PR is mergeable with owner awareness that the manual test log should accurately distinguish the primary MP4 from the two sidecar files. Suggested reviewers: 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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Inline comments:
In `@technical-documentation/testing/manual-e2e-checklist.md`:
- Line 452: Update the result row’s output wording so the .mp4 is identified as
the primary recording and only .cursor.json and .session.json are counted as
sidecars; use wording that states the MP4 and both sidecars were written,
without implying three sidecars.
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All good, thanks @naadydev |
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Selecting a window in the source picker aborted the ScreenCaptureKit
helper before it produced a single frame:
Assertion failed: (did_initialize), function CGS_REQUIRE_INIT,
file CGInitialization.c, line 44
The helper is a plain command-line executable, so nothing in it ever
connects to the window server. SCContentFilter(desktopIndependentWindow:)
resolves which display a window sits on by calling into SkyLight
(SLSGetDisplaysWithRect), and SkyLight asserts when CoreGraphics was
never initialised in the process.
Display capture is unaffected, because SCContentFilter(display:excludingWindows:)
is handed an already-resolved display and never asks SkyLight to resolve a
rect. That is why only the window branch of makeCaptureTarget crashed.
Touching any CoreGraphics display API performs the initialisation, so a
single CGMainDisplayID() at the top of main() is enough. CoreGraphics is
already imported; this avoids pulling AppKit into the helper or standing
up an NSApplication in a CLI process.
…ence the other one Wraps the CGMainDisplayID() side-effect call in initializeCoreGraphicsWindowServerConnection() so the SkyLight/CGS_REQUIRE_INIT rationale travels with a symbol name instead of sitting as a detached comment block at the top of main(), and notes at the other (unrelated) CGMainDisplayID() call site in makeCaptureTarget why it isn't the same thing.
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Summary
macOS window capture has never worked: picking any window in the source picker aborts the ScreenCaptureKit helper before it produces a frame, with
Assertion failed: (did_initialize), function CGS_REQUIRE_INIT, file CGInitialization.c, line 44.The helper is a plain command-line executable, so nothing in the process ever connects to the window server.
SCContentFilter(desktopIndependentWindow:)resolves which display a window sits on by calling into SkyLight (SLSGetDisplaysWithRect), and SkyLight asserts when CoreGraphics was never initialised.Display capture is unaffected, and that asymmetry is the whole story: the two branches of
makeCaptureTargetdiffer in exactly this respect —SCContentFilter(display:excludingWindows:)is handed an already-resolved display and never asks SkyLight to resolve a rect. Only thewindowbranch does, which is why the common path looks healthy while window capture is dead.Touching any CoreGraphics display API performs that initialisation, so one
CGMainDisplayID()at the top ofmain()is enough. CoreGraphics is already imported by this file, so the fix pulls in nothing new — no AppKit, and noNSApplicationstanding up inside a CLI process (NSApplication.sharedalso clears the assert; it is just a heavier way to buy the same initialisation).Also adds the manual E2E results-log row for the run below, per
AGENTS.md.Related issue
Fixes #487
Type of change
Release impact
Desktop impact
Screenshots / video
Not a UI change. The evidence is the helper's own event stream and the resulting files, below.
Testing
macOS 26.6.2 (25G83), Apple Silicon (M1).
swift build -c releaseis clean.1. Helper-level A/B — identical request JSON, only the binary differs. Same window id, same output path:
v1.10.0-rc.3(Developer ID signed, fromOpenscreen.app)Assertion failed: (did_initialize) … CGS_REQUIRE_INIT, SIGABRT, no fileready→recording-started→recording-stopped, 4.49s / 1336×840, decodes clean2. Full app pass — the installed rc.3, unmodified. Rather than patch a signed bundle, I pointed the existing
OPENSCREEN_SCK_CAPTURE_EXEoverride at a helper built from this branch, so the app keeps its Developer ID identity and its TCC grant, and only the helper changes. Main process confirms the override in[native-sck] starting macOS capture { helperPath: … }.Source picker → Windows tab → a window → Share → record → 25s → stop:
recording-1787475175449.mp4, 12,559,123 bytes, 25.18s / 2674×1684, decodes clean.mp4,.cursor.json,.session.json)Against 6/6 aborts on the shipped helper before the change, including one deliberate A/B run at the end to confirm the crash was still reproducible on the same machine, same window, minutes earlier.
Not covered. Webcam PiP, microphone and system audio (all off for these runs), export, GIF, AI/transcript sections, Windows, Linux.
No unit test.
Package.swiftdeliberately scopes the Swift test target to what is testable "without a screen, a display server or a TCC grant" — this crash needs all three, so it is only reachable from the manual pass. Worth noting the gap rather than papering over it: nothing in CI will catch a regression here, since CI is Linux-only.Summary by CodeRabbit
Bug Fixes
Testing
Documentation