Enum PageTransition 

pub enum PageTransition {
    None,
    M3SharedAxisX,
    M3FadeThrough,
    IosPush,
    SlideUp,
    Glyph,
    ReducedCrossfade,
    Custom(fn(f64, bool, Size) -> (Layer, Layer)),
}

The visual shape of a page transition. The navigator maps the active transition’s progress onto per-page geometry through resolve_layers.

#[allow(unpredictable_function_pointer_comparisons)]: the derived PartialEq/Eq compare a PageTransition::Custom payload by function pointer address, which the compiler flags because that address isn’t guaranteed stable across codegen units. Accepted here deliberately — the contract (documented on Custom) is a best-effort “names the same function” identity check, not a memory-safety- or correctness-critical comparison; the alternative (dropping Eq from the enum) breaks every other variant’s equality for a single edge case. The #[allow] sits at the enum level (not scoped to Custom alone) because a field-level attribute on a tuple-variant payload does not suppress a lint raised inside the derive macro’s generated PartialEq/Eq impl — confirmed by attempting exactly that scoping, which left the warning in place; the derive expands against the whole enum, so only an enum- or module-level #[allow] (or a hand-written impl PartialEq dropping the derive entirely) reaches it.

Variants

None

Instant switch — no animation. The default.

M3SharedAxisX

Material 3 shared-axis-X: a 30dp slide paired with a threshold cross-fade.

M3FadeThrough

Material 3 fade-through: a staged outgoing fade-out then incoming fade-in with the incoming [M3_FADE_THROUGH_SCALE_START]→1.0 scale-up — the verified Flutter FadeThroughTransition staging. See resolve_layers’s M3FadeThrough arm.

IosPush

iOS-style push/pop: incoming slides full-width from the edge; outgoing parallaxes by [IOS_PARALLAX_FRACTION] with an optional dim.

SlideUp

Bottom-sheet-style slide-up: the entering page translates in from the bottom (full height → 0); pop reverses (slides back down and out). The page below never moves (a modal sheet floats over a static page, unlike PageTransition::IosPush’s parallaxing below-page). Opacity is always 1.0 for both layers — a sheet’s scrim is a page-owned paint concern (the hosting widget paints/fades its own scrim, e.g. reading the transition progress itself or a fixed alpha), not a Layer-level effect this preset drives; see resolve_layers’s SlideUp arm.

Glyph

Glyph screen transition: a directional [GLYPH_SLIDE_DP]-px slide paired with a cross-fade. The entering screen slides in over the theme’s slow spatial timing while the leaving screen accelerates out over the faster exit timing (“exits always faster than entrances”); a pop reverses the slide direction. Timing is resolved from the active MotionScheme via resolve_spec/preset_enter_exit — pair it with Timing::ThemeDefault (or TransitionSpec::glyph).

ReducedCrossfade

Pure alpha cross-fade with zero geometric motion (no slide, no scale) — the resolve_spec reduce_motion collapse target (the Glyph design system’s hard accessibility rule: a reduced transition is a short linear cross-fade, never a zoom or slide). Selectable directly, but its primary role is the collapse; see resolve_layers’s arm.

Custom(fn(f64, bool, Size) -> (Layer, Layer))

A caller-supplied transition: a third-party design system’s escape hatch for authoring its own page transition without a matching built-in preset. The function maps raw progress (unclamped, so a spring overshoot is visible — the same raw value resolve_layers passes every built-in preset for position) plus is_pop and the page Size onto the (entering, leaving) Layer pair, exactly as a built-in preset’s resolve_layers arm does; resolve_layers invokes it verbatim, with no clamping or post-processing beyond what every preset gets.

A plain function pointer (not Box<dyn Fn>) so Custom keeps every derive PageTransition already has (Copy/Eq included) — a Box<dyn Fn> cannot implement either. Function pointers compare by address, so PartialEq/Eq stay meaningful: two Custom specs are equal iff they name the same function.

Timing. Custom has no MotionScheme tokens of its own — pair it with an explicit Timing::Duration/Timing::Spring for a caller-chosen timing, or Timing::ThemeDefault to fall back to the documented M3 default (300ms + Curve::Emphasized — preset_enter_exit’s fallback arm, matching make_driver’s unthemed ThemeDefault fallback).

Reduce-motion — programmatic path only. resolve_spec’s collapse to PageTransition::ReducedCrossfade applies to Custom like every other preset when a transition is staged programmatically (a push/pop/replace carrying a TransitionSpec): the navigator resolves it against the active reduce_motion flag on the transition’s first paint, before the preset is ever consulted, so a Custom fn staged that way is not called.

A user-driven interactive edge-swipe pop is a different path: it is not routed through that collapse at all — the navigator drives the popped page’s own preset directly, raw, with no resolve_spec step — so under reduce_motion the supplied function is still called there. This is not specific to Custom: every built-in preset behaves identically on an interactive pop (a pre-existing accessibility gap, unrelated to Custom and tracked separately — this doc narrows the claim to what the code does, it does not fix the gap).

Trait Implementations

impl Clone for PageTransition

fn clone(&self) -> PageTransition

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for PageTransition

impl Debug for PageTransition

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Default for PageTransition

fn default() -> PageTransition

Returns the “default value” for a type.

impl Eq for PageTransition

impl PartialEq for PageTransition

fn eq(&self, other: &PageTransition) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for PageTransition