[popups] Ignore pinch-zoom shifting

[atomiks]

Shared anchor positioning now switches shift() to the layout viewport only detection while pinch-zoomed, which keeps Navigation Menu and other popups from moving around when the visual viewport scales during pinch zoom, which is disorienting. It continues to support virtual software keyboard collision detection.

Changes

• Use the layout viewport for shift() when visualViewport.scale !== 1.
• Keep the existing context-menu behavior intact through the shared positioning path.

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@4485
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@4485
  

commit: cfd4aed

[mui-bot]

Bundle size report

Bundle	Parsed size	Gzip size
@base-ui/react	🔺+97B(+0.02%)	🔺+61B(+0.04%)

Details of bundle changes

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[flaviendelangle]

Code Review: [popups] Ignore pinch-zoom shifting

Rating: 4/5 ⭐⭐⭐⭐

Overview

This PR extends the existing layout-viewport-based shift() behavior — previously scoped only to context menus (shiftCrossAxis) — to all popups when the user is actively pinch-zooming (visualViewport.scale !== 1). This prevents disorienting popup movement during pinch zoom on touch devices.

What's Good

• Minimal, focused diff — net +4/−3 in a single file. The change is easy to reason about.
• Correct use of project utilities — uses ownerWindow() as required by project conventions, instead of accessing the global window directly.
• SSR-safe — win.visualViewport?.scale ?? 1 gracefully handles environments where visualViewport is undefined or null.
• Backward compatible — the shiftCrossAxis condition is preserved in the OR expression, so existing context menu behavior is untouched.
• Clean variable naming — useLayoutViewport clearly communicates intent and replaces a bare shiftCrossAxis that was harder to read in context.

Concerns

• Tests were added then removed — The first commit introduced well-structured unit tests that validated both the default behavior and the pinch-zoom case. The second commit deletes them entirely. This leaves the new visualViewport.scale code path without any test coverage. Could these tests be kept, perhaps adjusted to be less reliant on mocking Floating UI internals? Even a simpler assertion (e.g., verifying the useLayoutViewport logic in isolation) would improve confidence against regressions.

Minor Nits

• The dependency array at line 310 doesn't include visualViewport.scale, but this is correct — the value is read dynamically inside the callback each time Floating UI recalculates positioning, so it doesn't need to be a memoization dep.

Summary

Clean, well-scoped fix that correctly generalizes an existing safeguard. The only real concern is the removal of test coverage in the second commit — I'd love to see at least some test retained for the new behavior.

[atomiks]

This should be built into Floating UI as a string option due to floating-ui/floating-ui#3387 unless we implement that on our side. It's pretty rare to encounter but it does happen, so I'll try to do a release that handles this