paseo/docs/floating-panels.md

Floating Panels

Anchored popovers — tooltips, hover cards, dropdowns, autocompletes — that visually float above an anchor element on iOS, Android, and web. This doc captures the non-obvious traps. It is not a tutorial; it assumes you have seen the canonical files and are trying to add or change one.

Canonical files

File	Use case
components/ui/combobox.tsx	Anchored picker with search; mobile falls back to bottom sheet
components/ui/tooltip.tsx	Non-interactive hover/long-press tooltip
components/workspace-hover-card.tsx	Desktop-web hover card with measure + computePosition + Portal
components/ui/autocomplete-popover.tsx	Inline slash-command autocomplete above a focused TextInput

Each handles a different mix of concerns: combobox owns input focus, tooltip is non-interactive, hover-card is web-only desktop, autocomplete coexists with a focused TextInput. There is no shared "floating panel" primitive yet — when a fifth use case shows up we can revisit; until then prefer copying the closest file and trimming. The four gotchas below are what each of them re-learned.

Gotcha 1 — Android touch hit-test by parent bounds

On Android, a child View whose bounds fall outside its parent's bounds renders correctly (with overflow: visible, the default) but does not receive touch events. ViewGroup.dispatchTouchEvent filters touches by the parent's hit rect first, then iterates children. A touch in the overflowing region never reaches the parent, let alone the child. iOS and web do not share this rule — iOS hit-test descends into overflowing children, web uses standard CSS pointer events. This is the bug that put autocomplete on this path: the popover was positioned bottom: 100% of its parent and worked on iOS/web for months; Android touches sailed straight through to the chat scroll view behind it.

Two escape hatches in the codebase:

• Modal (combobox, tooltip on native) — opens a new Android window, so hit-testing starts fresh in that window. Side effect: a Modal opening on Android can detach the IME from an underlying TextInput. Fine for combobox (it has its own input) and tooltip (no input). Not fine for autocomplete (the composer's input must stay focused so the user keeps typing).
• <Portal> from @gorhom/portal (hover-card, autocomplete-popover) — hoists the React subtree to a fixed mount point (PortalHost name="root" in app/_layout.tsx) whose bounds cover the screen. Same window, same IME, hit-test works because the new parent is full-screen. This is the right default when you must keep IME attachment.

Choose Modal vs Portal by whether you need the underlying input to keep its keyboard.

Gotcha 2 — Portal breaks lifecycle and coordinate-system inheritance

A Portal escapes Android's hit-test, but it also escapes two things you were quietly relying on:

• Lifecycle. The portal'd subtree mounts at the app root, not inside your component's natural ancestor chain. When the user navigates away, your component may stay mounted (offscreen, in a tab) — the popover stays with it. Gate visible on a screen-focus signal. For panes inside agent-panel, the isPaneFocused prop already exists and flips on pane switches; pass visible={isYourOwnVisible && isPaneFocused}. See composer.tsx:1604 and autocomplete-popover.tsx.
• Transforms. The composer is wrapped in a Reanimated Animated.View with translateY: -keyboardShift (see use-keyboard-shift-style.ts). The chat content has the same transform applied (agent-panel.tsx:939). They move together because they share the SharedValue. A portal'd popover is at the app root — it does not get that transform unless you apply it yourself.

The fix for transforms is Gotcha 3.

Gotcha 3 — Reanimated transforms vs measureInWindow

measureInWindow returns the view's current screen position. In theory that includes Reanimated-applied transforms (Reanimated updates native view properties, and Android's getLocationInWindow reads transformed coords). In practice it's racy — the measurement may snapshot mid-animation, and on Android with Reanimated worklets the result is not always stable.

Do not try to track the keyboard by re-measuring on every frame. Instead, slave the popover's transform to the same SharedValue the composer uses:

1. Snapshot openShift = shift.value at the moment you measure the anchor.
2. Apply useAnimatedStyle(() => ({ transform: [{ translateY: openShift.value - shift.value }] })) to the popover wrapper.

When shift equals openShift, the translate is 0 and the popover sits at the measured position. When the keyboard moves afterward, the delta translates the popover by exactly the amount the composer translates. They move in lockstep, no re-measurement needed. See autocomplete-popover.tsx — openShift / shift / animatedTransformStyle.

Re-measure on Keyboard.addListener('keyboardDidShow'|'keyboardDidHide') only to refresh the snapshot if the keyboard was mid-transition when the popover opened.

Gotcha 4 — Status-bar offset for Portal-based positioning on Android

On Android, measureInWindow returns coords below the status bar (the status bar is system-owned space). A Portal overlay positioned at top: 0 inside the PortalProvider may start at the top of the window (above the status bar) depending on the wrapper chain. The result: position the popover at the measured rect.y and it sits StatusBar.currentHeight higher than the anchor on Android.

Mirror what tooltip does: shift the measured rect down by the status bar height on Android only.

const statusBarOffset = Platform.OS === "android" ? (StatusBar.currentHeight ?? 0) : 0;
setAnchorRect({ ...rect, y: rect.y + statusBarOffset });

See tooltip.tsx and autocomplete-popover.tsx. iOS and web do not need this.

Gotcha 5 — The two-measurement flash

If your popover needs top (or left) computed from both:

• the anchor's screen position (anchorRect from measureInWindow), and
• the popover's own size (contentSize from onLayout),

then a naïve implementation will flash through three positions on every open:

1. Frame 1 — render with top: -9999 (or any placeholder) while waiting for either measurement. Wrapper has no width, so the inner content lays out at its natural (often narrow) intrinsic width.
2. Frame 2 — anchorRect lands. Wrapper now has width: anchorRect.width. But the stale onLayout from frame 1 has already set contentSize to the narrow-width dimensions. top = anchorRect.y - wrongHeight - gap — visible at the wrong spot.
3. Frame 3 — real onLayout fires with the correct width. contentSize updates. Position snaps to the right place.

The visible jump in frame 2 is the flash. Two pieces solve it, and you need both:

• Do not mount the floating content until anchorRect is set. Return null until then. This prevents the bad-width onLayout from happening at all.
• Once anchorRect is set but contentSize isn't, render the wrapper with the final width but opacity: 0. The first visible paint is at the correct position. This is the combobox pattern — shouldHideDesktopContent at combobox.tsx:481, 876. Do not use top: -9999 as the placeholder; the layout work still happens at -9999 and any subsequent state-flash is visible when you flip back.

The "render invisible to measure, then reveal" pattern is the canonical solution to chicken-and-egg positioning in this codebase. Reach for it before anything fancier.

Recipe for a new anchored panel

Before you write a new one, ask:

1. Can the underlying input lose its keyboard? If yes, use Modal (simpler). If no, use Portal.
2. Does the panel need to dismiss on screen change? Almost always yes — gate visible on an upstream focus prop (isPaneFocused or similar).
3. Does the panel sit above something that moves with the keyboard? If yes, slave a Reanimated transform to the same SharedValue (Gotcha 3). If no, you can probably skip the transform entirely.
4. Will the panel's content height vary? If yes, you need both anchorRect and contentSize for positioning → apply Gotcha 5 (return null until anchor, then opacity-0 until contentSize). If no — content has a known fixed max height — you might be able to use bottom-anchored positioning (bottom: windowHeight - anchor.y + gap) and skip the contentSize round-trip entirely. But only if the height is genuinely bounded — autocomplete's inner detail card escapes the 220-cap container, which is why bottom-anchored looked clean but rendered wrong. Verify before you commit.
5. Are you on Android with Portal? Add the status-bar offset (Gotcha 4).

Then copy the closest canonical file and trim.