Struct FrictionSimulation 

pub struct FrictionSimulation { /* private fields */ }

Exponential drag decay: the iOS-style fling curve, and the friction phase of BouncingScrollSimulation.

drag is the fraction of velocity surviving one second and must sit in (0, 1). An optional constant deceleration subtracts a linear velocity term on top of the drag, for a caller that wants a fling to stop sooner than pure drag would; at 0.0 the curve is pure drag and only ever approaches FrictionSimulation::final_x.

Implementations

impl FrictionSimulation

pub fn new( drag: f64, position: f64, velocity: f64, tolerance: Tolerance, constant_deceleration: f64, ) -> Self

A drag curve from position at velocity px/s.

constant_deceleration is 0.0 for pure drag; a nonzero value is re-signed against velocity internally, so callers pass a magnitude.

pub fn through( start_x: f64, end_x: f64, start_velocity: f64, end_velocity: f64, ) -> Self

The drag curve that passes through both endpoints: at start_x moving start_velocity, at end_x moving end_velocity (Flutter’s FrictionSimulation.through, whose _dragFor is the exponential below). Settles within end_velocity, the speed the caller asked to arrive at.

pub fn final_x(&self) -> f64

Where the curve ends up: the drag asymptote under pure drag, the position at the final time once a constant deceleration stops it early.

pub fn time_at_x(&self, x: f64) -> f64

The time at which the curve reaches x, or f64::INFINITY if it never does (wrong side of the start, or beyond Self::final_x).

Inverts the pure-drag position, so with a nonzero constant deceleration the answer is an over-estimate of how far the curve actually gets — the same approximation Flutter’s timeAtX makes, and harmless for its one caller (BouncingScrollSimulation finding its edge crossing).

Trait Implementations

impl Clone for FrictionSimulation

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for FrictionSimulation

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

Formats the value using the given formatter.

impl Simulation for FrictionSimulation

fn is_done(&self, time: f64) -> bool

Settled once the velocity is within tolerance — or, with a constant deceleration, once that term has cancelled the drag term outright, which a zero velocity tolerance (a Self::through curve asked to arrive stopped) would otherwise never report.

fn x(&self, time: f64) -> f64

The position at time seconds.

fn dx(&self, time: f64) -> f64

The velocity at time seconds.