[transition] continue slide revivals from the removal's model frame - #6
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A slide insertion anchored its animation to the configured entry side, so reviving an in-flight removal was only continuous when the entry offset happened to cancel the leftover exit offset, which holds when the renderable enters from the side it exits to. A cross-side revival reset the residue and restarted from the entry side, teleporting the mid-flight renderable to the opposite edge. Anchor a revival's offset to the model frame the removal left behind: the offset cancels the model change for any side configuration, so the rendered position doesn't move at the revival instant, the leftover exit offset keeps decaying on top, and the velocity stays continuous. The renderable returns from wherever it is, and the configured entry side applies only to fresh insertions. The render pass applies the target frame as the model value before the insert transition runs, so the framework captures the removal's model frame at revival and passes it through the insert context as `revivalFrame`, set only when the insert transition takes over the removal's residue. The same-side/cross-side takeover distinction is deleted: the takeover is unconditional and both cases continue through the same mechanism.
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Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review. 📝 WalkthroughWalkthroughSlide transition revivals now continue from the removal’s current model position. ChangesSlide transition revival
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to The PR makes mid-flight slide revivals continuous across side configurations by anchoring insertion to the removal’s model position. Certain linear timing combinations can still briefly stall as the additive animations cancel velocity, so the change is mergeable with explicit owner awareness or follow-up. Sequence Diagram(s)sequenceDiagram
participant ComposeView
participant InsertTransitionContext
participant SlideTransition
participant RenderableLayer
ComposeView->>ComposeView: Capture the live removal position
ComposeView->>InsertTransitionContext: Pass revivalPosition
InsertTransitionContext->>SlideTransition: Provide revivalPosition
SlideTransition->>RenderableLayer: Add offset from revivalPosition
RenderableLayer->>RenderableLayer: Animate offset to zero
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #6 +/- ##
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+ Coverage 93.86% 93.88% +0.02%
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Files 96 96
Lines 5526 5546 +20
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+ Hits 5187 5207 +20
Misses 339 339
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`@ComposeUI/Sources/ComposeUI/ComposeNode/RenderItem/RenderableTransition`+Slide.swift:
- Around line 103-106: Update the revival handling in the position animation
within RenderableTransition so the new additive animation preserves the
in-flight removal animation’s velocity instead of applying an inverse offset
that cancels it. Replace the existing removal animation or continue from its
current velocity, and add a presentation-layer test covering a halfway-complete
linear removal.
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ComposeUI/Sources/ComposeUI/ComposeNode/RenderItem/RenderableTransition+Slide.swiftComposeUI/Sources/ComposeUI/ComposeNode/RenderItem/RenderableTransition.swiftComposeUI/Sources/ComposeUI/ComposeView/ComposeView.swiftComposeUI/Tests/ComposeUITests/ComposeNode/RenderItem/RenderableTransition+SlideTests.swiftComposeUI/Tests/ComposeUITests/ComposeView/ComposeView+TransitionTests.swiftplaygrounds/ComposeUIPlayground-iOS/ComposeUIPlayground-iOS/PlaygroundViews/Playground+TransitionRevivalView.swift
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The unconditional position takeover keeps the removal's leftover additive animation on a revival, and the zero-duration path returned before adding the cancelling insert offset, so the snap rendered the model change without any compensation: a renderable halfway out at exit + leftover snapped to target + leftover, the reflection of its position through the target, then drifted to rest as the leftover decayed. The previous cross-side behavior reset the residue, so its zero-duration revival was a clean snap. A zero-duration revival now removes the taken-over position animations before applying the end frame, mirroring the opacity transition, which strips residue before its own zero-duration guard. A delayed zero-duration revival keeps the composed behavior: continuous through the delay window, then the scheduled snap applies the target while any remaining leftover decays out.
The revival anchor was the renderable's frame, a derived measurement that breaks three ways when captured from a live system: a leftover non-identity transform inflates the frame to its bounding box, the AppKit view frame can lag a layer-only position write, and reconstructing a position from a frame goes through the anchor point, which an insertion hook can change between the capture and its use. Capture the root-layer model position instead. The taken-over residue's additive offsets are relative to that position, so it is the exact quantity the insertion anchors to, and the layer model position is unaffected by the transform, the anchor point, and the view/layer split. The slide insertion now anchors to a start position, derived from the start frame for a fresh insertion.
The fresh-insertion branch still wrote the start frame to the renderable, a leftover from when the animation read its start value back from the layer. The animation now anchors to the precomputed start position, so the write fed nothing: the model position was overwritten by the animation's model write in the same call, and the AppKit view frame write posts a frame-change notification that forces a layout pass. Both branches now purely compute the start position, and the insertion writes the target frame once before animating, matching the opacity insertion and making the completed-state contract explicit: the model rests at the target while the animation renders the offset from the start position.
A takeover matches key paths, not animation shapes: continuing by composition assumes additive residue, which the built-in transitions satisfy. The insertion context's revival position is captured before the render pass applies the target frame, earlier than the content update. The composed revival motion's quality depends on the timings: rest-starting curves keep the velocity continuous, an equal-duration linear pair cancels to a standstill, and strongly mismatched durations can overshoot. The revival playground page's slide configurations now revive identically, differing only in their sides.
The residue transitions now hand their insert context to the tests, so both halves of the framework contract are asserted: a taking-over revival receives the captured model position (also when the taken-over residue doesn't animate position), and a reset revival receives none. A delayed revival pin covers the composition that holds continuity through the delay window: the leftover stays attached while the scheduled insert offset holds the revival position through its fill mode. A hosted end-to-end test verifies the rendered position is continuous across a mid-flight cross-side revival, sampling the presentation before and after. The revival unit tests move to the insert transition section, and the changelog records the revival behavior change and the new context field.
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Summary
Reviving a renderable while its slide-out is in flight is now continuous for every side configuration. Previously, continuity held only when the transition entered from the side it exited to (the entry offset happened to cancel the leftover exit offset); a cross-side configuration (e.g.
.slide(from: .left, to: .right)) reset the residue and teleported the mid-flight renderable to the opposite edge before sliding it back in.The mechanism
A revival's insertion anchors its additive offset to the model position the removal left behind instead of the configured entry frame:
removalPosition + leftoverExitOffsettarget + (removalPosition − target) + leftoverExitOffset— the insertion's offset cancels the model change exactlyThe rendered position doesn't move at the revival instant, the leftover exit offset keeps decaying on top, and both animations settle into the resting position through the slide's existing additive stacking — no sampling or evaluator machinery, since position (unlike opacity) composes without clamping.
Semantics
fromside applies only to fresh insertions.takesOverKeyPaths: ["position"]is unconditional (same-side behavior is unchanged by construction).slide()): rest-starting curves (springs, ease-in-out) keep velocity continuous; an equal-duration linear pair cancels to a standstill until the leftover decays; strongly mismatched durations can overshoot before settling.Plumbing
The render pass applies the target frame as the model value before the insert transition runs, so
ComposeViewcaptures the removal's root-layer model position at revival time and passes it through a newInsertTransition.Context.revivalPositionfield — set only when the insert transition takes over the removal's residue,nilfor fresh insertions and reset revivals. The model position is unaffected by the layer's transform, anchor point, and the view/layer frame split, so hooks that change geometry between the capture and the transition can't corrupt the anchor. The takeover contract is documented as key-path-based with additive residue assumed (the built-ins satisfy it).Review provenance
Three independent strict reviews plus Codex/CodeRabbit triaged into five follow-up commits: the zero-duration reflection regression (fixed + pinned), the capture hardened from frame to model position, a vestigial entry-frame write removed (the insertion now rests its model at the target unconditionally), the contracts documented, and the test batch below. The remaining bot suggestion (replace stacking with sampled retargeting) is deliberately deferred and documented as the composition-quality trade-off.
Tests
.bothfill), and the framework contract (taking-over revivals receive the captured position — including when the residue doesn't animate position — reset revivals receive nil).Verification
Screenshot.2026-08-30.at.20.52.13.mp4
Screenshot.2026-08-30.at.20.53.42.mp4
Summary by CodeRabbit
Bug Fixes
Documentation