Struct ScrollMomentum 

pub struct ScrollMomentum { /* private fields */ }

Deterministic single-axis momentum used by virtualized collection widgets. Wheel input moves immediately; line-wheel impulses additionally feed this decay curve so detented wheels can traverse long collections without requiring one event per row.

Implementations

impl ScrollMomentum

pub fn set_view(&mut self, extent: f64, scrolls: bool, motion: EffectiveMotion)

The view extent long the give past the ends is measured against, whether the content scrolls along it (content that fits gives nowhere), and the motion the person allows (reduced: no give).

pub fn give(&self, now: Instant) -> f64

How far past an end the content is drawn at now, in whole device pixels: negative before the start.

pub fn give_needs_frame(&self, now: Instant) -> bool

Whether the give wants a frame: it springs back, or was drawn otherwise than it stands now.

pub fn new() -> ScrollMomentum

pub fn push(&mut self, delta: f64) -> f64

Add a logical-pixel wheel impulse. Return the immediate delta so the caller can apply it in the same input frame.

pub fn fling(&mut self, velocity: f64)

Continue from a content-space drag velocity after pointer release. The velocity is clamped to the same ceiling as accumulated wheel impulses, keeping a bad timestamp or synthetic pointer from launching the viewport an unbounded distance.

pub fn set_device_scale(&mut self, device_per_unit: f64)

How many device pixels one logical pixel is on the display the owner draws to (its event context’s scale factor).

pub fn advance(&mut self, now: Instant) -> f64

Advance the glide to now (the frame’s time) and return the logical-pixel displacement since the last step or since it started, in whole device pixels, carrying the rest to the next frame. A host that copies what stays on screen (crate::scroll_copy) moves whole pixels only: a glide in fractional steps would repaint its whole viewport every frame, the frames that most need to be cheap.

pub fn advance_by(&mut self, elapsed: Duration) -> f64

Advance the glide by elapsed and return the logical-pixel displacement, in whole device pixels like Self::advance: for a driver that keeps its own frame clock.

pub fn rest_distance(&self) -> f64

How much further the glide moves before it rests, in logical pixels, as Self::advance moves it: in whole device pixels, so what was moved plus this is where it lands. 0 at rest.

pub fn velocity(&self) -> f64

The glide’s speed, in logical pixels per second; 0 at rest.

pub fn stop(&mut self)

pub fn wheel( &mut self, delta: &MouseScrollDelta, phase: TouchPhase, reduce_motion: bool, ) -> WheelStep

Classify one vertical wheel event. Line (detented) wheels accelerate through Self::push; pixel (touchpad, touchscreen) deltas, in the display’s pixels, track the finger exactly in logical pixels (set the display’s scale first, Self::set_device_scale) and, when the gesture’s Ended phase arrives while still moving, continue as a fling. reduce_motion keeps every movement 1:1 with the input.

pub fn wheel_applied(&mut self, delta: f64, moved: f64) -> bool

Report how far the WheelStep::Scroll delta moved the content; returns whether the view moved, the content or its give. What fingers asked past an end pulls the content through the rubber band (Self::set_view); a delta refused whole with no give (at an edge, under reduced motion) stops momentum and forgets the gesture so an outer scroll region can take it over, fling included.

pub fn is_active(&self) -> bool

Trait Implementations

impl Clone for ScrollMomentum

fn clone(&self) -> ScrollMomentum

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ScrollMomentum

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

Formats the value using the given formatter.

impl Default for ScrollMomentum

fn default() -> ScrollMomentum

Returns the “default value” for a type.