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fix(portal): repaint the divider overlay only when it could have changed - #12009
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📝 WalkthroughWalkthrough
ChangesDivider overlay repaint gating
Priority: ⬇️ Low Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant HostedViewSync
participant WindowTerminalPortal
participant SplitDividerOverlayView
HostedViewSync->>WindowTerminalPortal: Synchronize hosted view
WindowTerminalPortal->>SplitDividerOverlayView: Compare placement and render inputs
WindowTerminalPortal->>SplitDividerOverlayView: Request repaint when changed
SplitDividerOverlayView->>SplitDividerOverlayView: Walk the window view tree
Suggested reviewers: Merge Risk: 🔵 Low · up to A narrow lifecycle path can leave stale divider pixels after a hosted view is hidden. Add the final-state refresh before merging. Important Pre-merge checks failedPlease resolve all errors before merging. Addressing warnings is optional. ❌ Failed checks (1 error, 1 warning)
✅ Passed checks (23 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 56.25% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 16 functions across 3 files. (1 skipped: 1 unsupported.) Full details: Cmux No Ambient Global StateExplanation The PR adds ambient mutable state at Resolution Move the repaint count to scoped state. Prefer a constructable diagnostics recorder owned by ✨ Finishing Touches🧪 Generate unit tests (beta)
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In `@cmuxTests/PortalDividerOverlayRepaintTests.swift`:
- Line 31: Replace fixed-duration realizeWindowLayout waits with deterministic
layout-settlement handling: at cmuxTests/PortalDividerOverlayRepaintTests.swift
lines 31-31 and 76-76, use the deterministic helper before binding the portal;
at lines 45-45 and 90-90, await the layout-completion predicate before sampling
the repaint baseline. Use a real completion signal or deadline-bounded poll, not
a fixed sleep.
In `@Sources/TerminalWindowPortal.swift`:
- Line 1261: The batch path in synchronizeAllHostedViews should avoid per-entry
signature invalidation: have each synchronizeHostedView invocation use only
overlay placement, then compute and compare externalGeometrySignature once after
all eligible hosted views are synchronized. Keep direct single-entry
synchronization behavior unchanged, including its existing ensureInstalled and
ensureDividerOverlayOnTop handling.
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Inline comments:
In `@Sources/TerminalWindowPortal.swift`:
- Around line 1286-1288: Update HostedGeometrySignature to include an
overlay-renderable flag derived from !hostedView.isHidden && hostedView.window
!= nil, so externalGeometrySignature changes when a hosted view is hidden,
revealed, attached, or detached without a frame change. Ensure
SplitDividerOverlayView.draw invalidates accordingly, and add regression
coverage for hiding and revealing a hosted view with an unchanged frame.
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Inline comments:
In `@Sources/TerminalWindowPortal.swift`:
- Line 2485: Update the direct synchronization function containing
refreshDividerOverlayIfGeometryChanged() to install a function-level defer when
deferDividerOverlay is false, invoking the overlay geometry comparison on every
exit path, including early returns. Remove the normal-path-only call so each
synchronization compares the final overlay state exactly once.
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| if !deferDividerOverlay { | ||
| ensureDividerOverlayOnTop() | ||
| refreshDividerOverlayIfGeometryChanged() |
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🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win
🔎 Supported by static analysis
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rg -n -C 3 'occludingHostedFrames|renderInputs|updateEntryVisibility|synchronizeHostedView|lastDividerOverlayRenderInputs|needsDisplay' Sources/TerminalWindowPortal.swift cmuxTests/PortalDividerOverlayRepaintTests.swiftRepository: manaflow-ai/cmux
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printf '\n--- visibility implementation ---\n'
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Refresh the overlay after every direct synchronization exit.
Line 2485 runs only on the normal exit path. Earlier branches can hide a hosted view and return. Because renderInputs() excludes hidden hosted views, this changes the overlay draw inputs without requesting a repaint. Stale divider pixels can remain visible.
Install the comparison as a function-level defer when deferDividerOverlay is false. This ensures that every direct synchronization compares the final overlay state.
Proposed fix
guard portalIsPrepared || ensureInstalled(syncLayout: syncLayout) else { return }
+ defer {
+ if !deferDividerOverlay {
+ ensureDividerOverlayOnTop()
+ refreshDividerOverlayIfGeometryChanged()
+ }
+ }
guard var entry = entriesByHostedId[hostedId] else { return }
...
- if !deferDividerOverlay {
- ensureDividerOverlayOnTop()
- refreshDividerOverlayIfGeometryChanged()
- }🤖 Prompt for AI Agents
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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In `@Sources/TerminalWindowPortal.swift` at line 2485, Update the direct
synchronization function containing refreshDividerOverlayIfGeometryChanged() to
install a function-level defer when deferDividerOverlay is false, invoking the
overlay geometry comparison on every exit path, including early returns. Remove
the normal-path-only call so each synchronization compares the final overlay
state exactly once.
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review. Visit https://docs.coderabbit.ai/cli?utm_source=ghpr
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Thanks, love this one! One thing from the rebase: |
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Fixed in e24d93f, both halves: (1) the z-order invariant is now 'divider overlay above the hosted terminal views' rather than 'last subview', with an O(1) fast path for the settled state, so pane-swap hoisting no longer flips it back (your ping-pong read was exactly right); (2) the CodeRabbit finding (compare-only-on-fallthrough) is installed as a function-level defer. Added regression tests: z-order stability across repeated syncs, divider-above-hosted + paneSwap-above-divider ordering, and early-exit-with-hidden-view still repainting. |
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Thanks for the z-order fix, that was exactly it! I pushed a small follow-up on top so this can land: merged main and dropped the stale |
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Correction to my earlier comment: head 8fa020a still selected the LOWEST hosted view above the divider (.first(where:)), so with 2+ hosted views above it one sync cleared only the bottom one. Fixed and pushed as 01dfd7b: the placement reference is now the TOPMOST hosted view (.last(where:)), one re-add clears the whole run; fixture binds two real surfaces and the two-intruder test asserts BOTH indices below the divider after one sync, paneSwap above; paneSwap presence assertion is now unconditional (XCTUnwrap). |
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Correcting the two-intruder coverage on my last commit (5f8b18f): its premise used Also reporting verification limits honestly: the focused AppKit regression has NOT been executed locally. Per the repo's trust-boundary policy I did not run candidate PR code on this host, and the maintainer-dispatch path (scripts/ci/dispatch-focused-test.py) returned HTTP 403 (admin workflow dispatch + repo variables required), so I could not schedule it on upstream CI either. Can an authorized maintainer run: |
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Thank you for the render-input gating approach and the original regression tests. At the manager’s request, I preserved your four original commits in #14576, merged current main, moved snapshot ownership and repaint diagnostics into the overlay, and covered stable pane-swap stacking, early-return hiding, and direct detach/unmount. Your authorship is retained and the fixup is co-authored. This PR remains open for you and the maintainers to coordinate; I have not closed it. — Cairnfinch · registration pending |
SplitDividerOverlayView.draw walks the whole window view tree from contentView before it looks at dirtyRect, so every invalidation of that overlay costs a full-hierarchy traversal however small the dirty region. ensureDividerOverlayOnTop ends by invalidating unconditionally, and synchronizeHostedView calls it per hosted view per geometry tick. In a 20-second sample of an idle app that walk was the heaviest cmux frame on the main thread: 34 of the 779 busy samples, 4.4% of main-thread work with nothing on screen moving. The counter lives next to the sizing counters because it guards the same kind of bug they do. The window-move echo storm was a pass that had nothing to do scheduling work anyway; so is this. Two tests, because gating an invalidation can fail in both directions. A sync that changed nothing must not repaint. A hosted view that actually moved still must, or the overlay paints divider lines at stale positions after a split resize. First of two commits. This one adds the counter and the tests against today's unconditional invalidation, so the idle test fails and CI shows the bug is real before the fix lands. Claude-Session: https://claude.ai/code/session_01Bj791kgph6Xk9CJf9c41Db
ensureDividerOverlayOnTop ended with an unconditional needsDisplay. The guards above it are careful, touching the view only when the overlay's superview, z-order, or frame is actually wrong, and then it repainted anyway. SplitDividerOverlayView.draw walks the entire window view tree from contentView looking for NSSplitViews and only consults dirtyRect afterward, so each of those repaints cost a full traversal. Gate it on placement changing or on ExternalGeometrySignature moving. That signature is the right condition because shouldRenderOverlay paints a segment only where a portal-hosted surface crosses the divider centerline, and those rects come from the same hosted views the signature fingerprints. Dragging a divider resizes the panes beside it, which arrives as changed hosted frames. Adding or closing a split changes the entry set instead. The signature also excludes the window origin, so a titlebar drag still does not repaint. Three syncs of an unmoved hosted view went from 6 repaints to 0. Six because each synchronizeHostedViewForAnchor reaches this twice. Claude-Session: https://claude.ai/code/session_01Bj791kgph6Xk9CJf9c41Db
Review catch, and a real regression in the previous commit. ensureDividerOverlayOnTop runs twice per synchronizeHostedView, once through ensureInstalled and once at the end, and synchronizeAllHostedViews runs that per entry. Putting externalGeometrySignature inside it made a batch O(entries squared) where it had been O(entries). The comment in synchronizeAllHostedViews already warns that a session of mirrored tmux windows keeps dozens of hidden surfaces, which is exactly the case this would have slowed. The doubling was visible in the previous commit's own test output, 6 repaints for 3 syncs, and I read past it. Split the two jobs. ensureDividerOverlayOnTop is placement only and cheap again. refreshDividerOverlayIfGeometryChanged owns the signature compare, and synchronizeAllHostedViews sets a flag so its entries skip it and the batch pays once at its boundary. Single-entry syncs are unchanged. Swept the file for siblings: externalGeometrySignature now has three call sites, two of them the pre-existing synchronizeLayoutHierarchy pair, and none sits inside a loop over entriesByHostedId. Also drop the fixed-duration layout wait from the tests. realizeWindowLayout ends in a 50ms run-loop spin; layout settling after it on a loaded worker would repaint inside the measured window and fail the test for the wrong reason. Poll the real predicate instead, syncing until a sync stops producing repaints, bounded at 50 attempts. The four copies of the setup are now one fixture. Claude-Session: https://claude.ai/code/session_01Bj791kgph6Xk9CJf9c41Db
Review catch. The gate compared the portal's hosted-frame signature, but that is not the set the overlay draws from. hostedFramesLikelyToOccludeDividers drops hidden and windowless surfaces, and the overlay paints a segment only where one of the surviving rects crosses a divider centerline. HostedGeometrySignature records frames only, so hiding a surface compared equal and left divider pixels that should have been repainted. A hidden entry keeps its frame on purpose, as synchronizeAllHostedViews says, so this was the ordinary case. Ask the overlay for its own render inputs instead: its bounds plus the frames that helper returns. One source, so the gate cannot drift from the drawing again, which is how this bug happened. Kept ExternalGeometrySignature out of it. That type answers a different question for synchronizeLayoutHierarchy, and its contents are tuned for terminating the sync echo chain; adding a visibility field would have made every hide and reveal escalate to a full layout pass. Bounds and hosted frames are window-relative, so a titlebar drag still costs nothing. Also repaint on viewDidChangeEffectiveAppearance. overlayDividerColor resolves each split view's dividerColor against the current appearance, and no geometry comparison can see a theme change. New test hides a hosted view through updateEntryVisibility and asserts the frame did not move, so it fails if the repaint ever comes from something other than the visibility change. Claude-Session: https://claude.ai/code/session_01Bj791kgph6Xk9CJf9c41Db
…y on every sync exit Two defects in the overlay maintenance path: 1. ensureDividerOverlayOnTop demanded dividerOverlayView be hostView's LAST subview, but markDividerOverlayNeedingDisplay raises paneSwapOverlayView above it (by design: pane swap must hit-test on top of the divider). So after any mark, the next ensure saw subviews.last != divider and re-added the divider on top + repainted, which hoisted pane-swap again, and the pair swapped every synchronizeHostedView with a full-tree repaint each time. The invariant is now 'divider above the hosted terminal views'; pane-swap may keep sitting above it. Placement comparison uses the hosted-view set instead of subviews.last. 2. CodeRabbit finding (c503c67c): the geometry comparison ran only on synchronizeHostedView's fallthrough. Earlier exits (missing anchor or window, anchor-window mismatch) hide hosted views, the overlay's render inputs exclude hidden/windless surfaces, so the paint inputs changed with nothing comparing them: stale divider pixels. The ensure+compare now installs as a function-level defer gated on deferDividerOverlay and isBatchSynchronizingHostedViews, and the normal-path copy is gone. Regression tests added: z-order stays put across repeated syncs with a pane-swap overlay present, no repaint when nothing changed, and early return paths (missing anchor) still refresh the overlay.
The ensureDividerOverlayOnTop comment still described gating the repaint on ExternalGeometrySignature, which the overlay no longer does (the comparison lives in refreshDividerOverlayIfGeometryChanged, on the overlay's own render inputs), and ran into the current description. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…ider The prior selection used .first(where:) over the above-divider subview slice, which is the LOWEST such view in index order (first in front-to-back iteration dynasty of NSView subviews is back-to-front, so 'first' from that end is the bottom of the above-divider run). With two or more hosted views above the divider, one sync moved the divider above only the bottom-most intruder and left the rest of the run on top, so full convergence needed a sync per intruder and the divider could sit under hosted views in between. Select the highest-index hosted view from the above-divider slice (.last(where:)), which a single re-add clears all of them at once. The settled case still costs no scan: the divider-as-last-subview fast path answers without touching the slice. Also: the previous 'settled' fast path missed a real churn shape where paneSwap ends up above the divider after hosted views are re-added elsewhere (the divider is no longer last). The pre-divider-index guard only answers when the divider exists; that is now handled before the last-subview check, and intruders above are detected from the actual divider position, not assumed away. Regression added: two-hosted-intruder state (divider deliberately sunk below a hosted view) converges in one sync with paneSwap reinstalled above it; the z-order stability test now asserts paneSwap presence unconditionally instead of skipping when the fixture did not install it.
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@teamleaderleo — status ping on the three still-open PRs, all freshly rebased onto current
Each rebase is content-identical to its previous head (verified by patch-id), so nothing substantive changed — pure base refresh. CLA passes, zero failing checks on all three. Verification gap I want to flag rather than bury: the focused AppKit regression in #12009 has not been executed. I could not run it locally (repo trust boundary) and That test is the only thing standing between #12009 and a fully-green story as far as I can tell. For #10351 and #5848 the only evidence so far is syntax parsing and conflict-marker absence — no test target was compiled or executed for either one. No rush on any of it, and thanks for the careful reviews — both catches were real bugs, not nits. |
…case The premise assertions compared indexes in the wrong order, and the sink placed the divider below only the second hosted view, so the first one never intruded. Sink below the lower hosted view and assert the divider index is below both. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Pushed a small follow-up so this can land: merged main, and the multi-intruder test now sinks the divider below both hosted views (its premise checks had the index order flipped). Thank you for this :) |
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Merged, thank you @STRML!! The divider overlay now repaints only when its geometry or stacking actually changes, which takes the heaviest idle main-thread work off the table. :D |
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Status: rebased onto
main(623e5bcbb80) as a linear 4-commit stack, no merge commits. Three conflicts, all inSources/TerminalWindowPortal.swift(upstream extractedSplitDividerOverlayViewinto its own file in a954706 and moved split-terminal sync into a transaction in a9547067a95): the overlay's paint helpers now live inSources/TerminalWindowPortalDividerOverlayView.swift(plus the newRenderInputsgate inputs), and the per-entry sync keeps upstream'sdeferDividerOverlaybranch while running this PR's geometry refresh only outside batch syncs. Local clean build blocked by an unrelated Xcode 27 issue that reproduces on pristinemain(CodexTurnRestoreIntentPolicy.swiftcannot seeRestorableAgentProcessLivenessfrom theCmuxWorkspacespackage); CI is the arbiter.Reviewer's guide
ensureDividerOverlayOnTop,refreshDividerOverlayIfGeometryChanged,markDividerOverlayNeedingDisplayandSplitDividerOverlayView.RenderInputsinSources/TerminalWindowPortal.swift. The gate compares the overlay's own render inputs, so it cannot drift from whatdrawpaints.cmuxTests/PortalDividerOverlayRepaintTests.swift. Red-then-green: the first commit adds the two failing tests, the second the fix.Sources/Debug/RemoteTmux/TerminalWindowPortal+DebugDiagnostics.swift(the counter).Summary
The divider overlay repainted on every portal sync, including syncs that changed nothing, and each repaint walks the whole window view tree.
ensureDividerOverlayOnTop()ended with an unconditionaldividerOverlayView.needsDisplay = true. The two guards above it are careful, touching the view only when the overlay's superview, z-order, or frame is actually wrong. Then it repainted anyway.SplitDividerOverlayView.drawwalks the entire window view tree fromcontentViewlooking forNSSplitViews, and only consultsdirtyRectafter that walk, so a one-pixel dirty region still costs a full traversal.synchronizeHostedViewcalls it once per hosted view per geometry tick.This gates the invalidation on whether what the overlay draws could have moved.
Measurement
20-second
sampleof cmux 0.64.22 sitting idle, no window interaction:SplitDividerOverlayView.collectDividerSegmentsSplitDividerOverlayView.draw(self)Main thread took 11527 samples, 10748 of them parked in
mach_msg2_trap. Of the 779 that were real work, the divider walk was 34. That is 4.4%, and the heaviest single cmux frame on the main thread in an app doing nothing.34 vs 4 also says the walk is 89% of the repaint, so the fix has to avoid the walk, not the fill.
The gate is cheaper than what it prevents: in a second sample under load,
externalGeometrySignature()cost 2 samples againstcollectDividerSegments's 14.The regression test measures the same thing directly. Three syncs of a hosted view that has not moved:
Six, not three, because each
synchronizeHostedViewForAnchorreachesensureDividerOverlayOnToptwice.What the gate compares
shouldRenderOverlaypaints a segment only where a portal-hosted surface crosses that divider's centerline, and those rects come fromhostedFramesLikelyToOccludeDividers(). So the gate asks the overlay for its own render inputs: its bounds, plus exactly the frames that helper returns. One source for both, so the comparison cannot drift from the drawing.Dragging a divider resizes the surfaces on either side, which changes those frames. Adding, closing, hiding or revealing a split changes which frames the helper returns at all. Bounds and hosted frames are window-relative, so moving the window by its titlebar still costs nothing, which is the property the window-move echo storm taught this file to protect.
An earlier revision of this PR compared
ExternalGeometrySignatureinstead, and CodeRabbit was right to flag it. That type records hosted frames, while the helper above also filters out hidden and windowless surfaces, and a hidden entry keeps its frame on purpose. Hiding a surface therefore compared equal and left stale divider pixels. WideningExternalGeometrySignaturewould have fixed the comparison at the cost of making every hide and reveal escalate to a full layout pass insynchronizeLayoutHierarchy, so the overlay got its own inputs instead.Appearance is the one input no geometry comparison can see, since
overlayDividerColorresolves each split view'sdividerColoragainst the current appearance.viewDidChangeEffectiveAppearancerepaints for that.Tests
Red-then-green per the repo policy. The first commit adds the first two against today's unconditional invalidation, so CI shows the idle test failing before the fix lands.
testRedundantHostedViewSyncDoesNotRepaintDividerOverlay: three syncs of an unmoved hosted view must not invalidate.testMovedHostedViewRepaintsDividerOverlay: the other direction. A gate like this can fail by never invalidating at all, which would leave divider lines painted at stale positions after a split resize.testHidingHostedViewWithoutMovingItRepaintsDividerOverlay: hides a surface throughupdateEntryVisibilityand asserts the frame did not move, so it fails if the repaint ever comes from something other than the visibility change.They settle with a deadline-bounded poll rather than a fixed wait: sync until a sync stops producing repaints, bounded at 50 attempts.
realizeWindowLayoutends in a 50ms run-loop spin, and layout settling after that on a loaded worker would repaint inside the measured window and fail a test for the wrong reason.The counter they assert on,
RemoteTmuxSizingDiagnostics.dividerOverlayRepaintCount, sits with the existing sizing counters because it guards the same class of bug.Related
Fourth idle-work fix in this area, all found in the same profiles:
https://claude.ai/code/session_01Bj791kgph6Xk9CJf9c41Db
Summary by CodeRabbit
Bug Fixes
Tests