refactor(motion): one release policy, resolveSnapPoint, on selectSnapPoint by cixzhang · Pull Request #8663 · meta/astryx

cixzhang · 2026-10-27T07:41:43Z

User impact

None directly: no behavior changes. Where a drag's release lands (a sheet's detent, a pager's page, a snap point) is now decided by one internal helper, so every gesture that settles on a set of positions, including the upcoming public drag-to-snap-points API, follows the same rules instead of each keeping its own copy.

Change

motion/resolveSnapPoint.ts (new, internal) is the release policy, on the existing selectSnapPoint primitive:
- A slow release lands on the snap point nearest where it would come to rest (its position, or its projected coast).
- A flick (flickThreshold or faster) goes at least to the next snap point in its direction.
- With start, a release moving back toward where the drag began cancels to it (AST-094 FR37).
- With fromIndex and maxSteps, it moves at most that many points (a pager's one page per release).
motion/projection.ts keeps selectSnapPoint as the math primitive. Paging moves out to motion/selectPage.ts, which is built on resolveSnapPoint.
README rows are updated. The changeset is internal ([chore]).

Nothing on main imports paging from projection.ts, and resolveSnapPoint is not exported from the package (a test locks that).

Relationship

This is the motion half of #8565, split out so it can land on main ahead of the bottom-sheet stack. #8565 keeps only the bottom sheet's adoption. The public createDragToSnapPoints (#8658) can then call resolveSnapPoint instead of carrying its own copy of the same rules.

Testing

Core tsc: clean.
The motion suite passes (549), including resolveSnapPoint.test.ts (flick, cancel, step limit, projection, tolerance, ties) and selectPage.test.ts.
check:changesets is clean, and ESLint is clean on the changed files.

…Point Where a release lands is decided in one place: motion/resolveSnapPoint.ts. A slow release lands on the snap point nearest where it would rest; a flick (flickThreshold or faster) goes at least to the next snap point in its direction; with start, a release moving back toward it cancels to it (spec:AST-094 FR37); with fromIndex and maxSteps it moves at most that many points. selectSnapPoint in projection.ts stays the math primitive, and paging moves to selectPage.ts on top of resolveSnapPoint. Internal: not exported from the package (a test locks that). No behavior change. Split from #8565 so the public drag-to-snap-points API can build on it; #8565 keeps the bottom sheet's adoption.

vercel · 2026-10-27T07:41:48Z

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astracat-bot · 2026-10-27T07:42:07Z

AI review status for this pull request.

Review status	Updated
🟢 Reviewed (for maintainers only)	Oct 27, 2026, 8:17 AM UTC

github-actions · 2026-10-27T07:49:46Z

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…snap points The motion README keeps this branch's Files table and takes meta#8663's rows: resolveSnapPoint.ts and selectPage.ts, and projection.ts without paging.

…se policy says The factory now calls resolveSnapPoint (meta#8663) with the snap points, the release position and velocity, flickThreshold and the drag's start, instead of a release rule of its own: the nearest snap point, the next one past the flick speed, and back to where the drag started when the release moves back toward it (spec:AST-094 FR37). Its own snapPointAfterRelease and nearestIndex are gone; the starting snap point comes from the same policy. The pure-rule tests now check FR2's and FR37's cases through that call, and the touch tests are unchanged.

astracat-bot

This looks ready to approve: resolveSnapPoint stays internal, its projection and moving-back cancel follow AST-094 FR3 and FR37 with thresholds left to callers (AST-100 FR3), and selectPage keeps its exact behavior after the move. Nothing is required; one optional hardening before a public caller such as #8658 passes thresholds through: a still release with flickThreshold: 0 is treated as a downward flick, which a velocity !== 0 guard on the flick branch (as the cancel branch already has) would prevent.

[Automated review]

astracat-bot · 2026-10-27T08:17:10Z

+    maxSteps,
+  });
+  let index = choice.index;
+  if (Math.abs(velocity) >= flickThreshold) {


Optional hardening: with flickThreshold: 0, a still release (velocity === 0) enters this branch and the else arm walks down the axis, so resolveSnapPoint({points: [0, 300, 640], position: 300, velocity: 0, flickThreshold: 0}) returns index 0 instead of 1. A velocity !== 0 guard here, as the cancel branch below has, keeps a still release from flicking if a caller-supplied threshold ever reaches 0.

…) into meta#8068 The motion README's table takes main's rows (resolveSnapPoint.ts, selectPage.ts) plus this PR's uikit/sheet.ts row. The sheet's rule still calls selectSnapPoint, which meta#8663 keeps.

…xperimental touch exports The motion README's Files table is the union: main's rows, with meta#8663's resolveSnapPoint.ts and selectPage.ts, plus this branch's, in main's order. # Conflicts: # packages/core/src/motion/README.md

The motion README's Files table is the union: main's rows, with meta#8663's resolveSnapPoint.ts and selectPage.ts, plus this branch's, in main's order. # Conflicts: # packages/core/src/motion/README.md

…#8270

…) into meta#8309

…) into meta#8315

…) into meta#8336

…) into meta#8320

…; this pull request's presentation.ts rows kept beside them) into meta#8293

…) into meta#8356

…tor's browser proofs The motion README's Files table is the union: main's rows, with meta#8663's resolveSnapPoint.ts and selectPage.ts, plus this branch's, in main's order. # Conflicts: # packages/core/src/motion/README.md

…licy) into the public animator

…) into meta#8358

…) into meta#8360

…licy) into the animator's presentation start

…eta#8663) into c02-8124-base

…eta#8663) into uikit/c02-switch-touch, through c02-8124-base

meta#8627's dependencies in one commit, so its compare link shows only its own change: meta#8298 (the presentation resolver) and meta#8076 at 3fb31dd, which carries main's meta#8663.

The base: the determinate fill on the compositor (meta#8196 de43cd2) and the touch foundation (meta#8076, with main through meta#8663).

…for main's meta#8663 README conflict) into the keyboard clearance

…eta#8663; the gesture-free test pins the utils entry only) into the AlertDialog tracking base

…policy Main now has one release policy, `motion/resolveSnapPoint.ts` (meta#8663): "the one 'where does a release land' helper ... a component's release rule calls it with its own points and thresholds". `paging.ts`'s own `selectPage` was a second one, so it goes: the pager (meta#8146) picks the page with these measured thresholds through `resolveSnapPoint`. The thresholds stay in the paging table (`paging.release`), and their measured page-choice tests move with the rule. The scroll table keeps its `scroll.paging` estimates: main's `motion/selectPage.ts` reads `scroll.paging.projectionRate`.

`pageForRelease` is the pager's release rule on main's release policy, `motion/resolveSnapPoint.ts` (meta#8663), with UIKit's measured paging thresholds from `paging.release`: a flick from the advance speed on, the nearest page below it, a release moving back toward the start page settling there (spec:AST-094 FR37) through `start`, and at most one page from the start page through `maxSteps`. A looping pager passes only the pages within reach of its start page, so the target may leave the range and the owner wraps it. The measured page-choice tests move here from paging.test.ts. One test released at exactly half a page: past the pan's 10 pt claim its "90 px" drag moved the content 80 px. The policy settles an exact tie on the earlier page; UIKit's measured rule is "past half a page, the next one", so the finger now moves 100 px and the content travels the 90 px the test describes.

cixzhang requested review from imdreamrunner and josephfarina as code owners October 27, 2026 07:41

cixzhang force-pushed the feat/resolve-snap-point branch 2 times, most recently from 57a240e to c85d092 Compare October 27, 2026 07:43

cixzhang mentioned this pull request Oct 27, 2026

feat(core): createDragToSnapPoints and useDragToSnapPoints settle an element on snap points #8658

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cixzhang merged commit 6aea9bd into main Oct 27, 2026
81 of 117 checks passed

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge meta#8076 (main's meta#8663 rows in motion/README.md) into meta…

170162d

…#8270

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge facebook#8270 (facebook#8076: main's facebook#8663 rows in moti…

58dbb1a

…) into meta#8309

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge facebook#8309 (facebook#8076: main's facebook#8663 rows in moti…

2e77071

…) into meta#8315

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge facebook#8315 (facebook#8076: main's facebook#8663 rows in moti…

3b1b26d

…) into meta#8336

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge meta#8336 (meta#8076: main's meta#8663 rows in motion/README.md…

ca71fce

…) into meta#8320

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge facebook#8320 (facebook#8076: main's facebook#8663 rows in moti…

fe527be

…; this pull request's presentation.ts rows kept beside them) into meta#8293

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge facebook#8293 (facebook#8076: main's facebook#8663 rows in moti…

52e5eb7

…) into meta#8356

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge meta#8076 (3fb31dd: main 6aea9bd merged, meta#8663's release po…

506d702

…licy) into the public animator

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge facebook#8356 (facebook#8076: main's facebook#8663 rows in moti…

c5465c2

…) into meta#8358

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge facebook#8358 (facebook#8076: main's facebook#8663 rows in moti…

0dd683d

…) into meta#8360

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge meta#8076 (3fb31dd: main 6aea9bd merged, meta#8663's release po…

9718a3d

…licy) into the animator's presentation start

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge meta#8270 (170162d: F2's fZ2, with meta#8076 3fb31dd and main's m…

3f97cf4

…eta#8663) into c02-8124-base

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge meta#8270 (170162d: F2's fZ2, with meta#8076 3fb31dd and main's m…

9d50b76

…eta#8663) into uikit/c02-switch-touch, through c02-8124-base

vjeux mentioned this pull request Oct 27, 2026

fix(core): gesture hooks follow their element; recognizer plumbing is protected #8315

Closed

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge meta#8076 (3fb31dd): main with meta#8663, and the touch layer

c4c6e4d

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge meta#8076 (3fb31dd) into this PR's base

082f5f9

The base: the determinate fill on the compositor (meta#8196 de43cd2) and the touch foundation (meta#8076, with main through meta#8663).

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge meta#8076 (3fb31dd): main with meta#8663, and the touch layer

842a8ee

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge the foundation fold (meta#8186 1aaf2db with meta#8076 3fb31dd, …

b54633d

…for main's meta#8663 README conflict) into the keyboard clearance

vjeux added a commit to vjeux/astryx that referenced this pull request Oct 27, 2026

Merge meta#8360 (5588013: F2's line on meta#8076 3fb31dd, main with m…

96b1030

…eta#8663; the gesture-free test pins the utils entry only) into the AlertDialog tracking base

vjeux mentioned this pull request Oct 27, 2026

feat(Slider): the thumbs track as a pan for every pointer #8669

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4 tasks done

github-actions Bot deleted the feat/resolve-snap-point branch October 28, 2026 06:17

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refactor(motion): one release policy, resolveSnapPoint, on selectSnapPoint - #8663

refactor(motion): one release policy, resolveSnapPoint, on selectSnapPoint#8663
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