Tween

TypeScript lib for animating using spring physics tweens to any dimension.

Usage

1. Initialize

   import { spring } from "@pomle/tween";
      
   const tween = spring({valueA: 0, valueB: 2});
   tween.to({valueA: 3, valueB: 4});

2. Update & Read

   // Returns true when change made
   if (tween.update(1/60)) {
     const values = tween.values;
     console.log("New values", values);
   }

Mutation

Input object will be mutated on update. Depending on your use case you may either supply the reference you need updated, or supply a copy.

Setup

import { spring } from "@pomle/tween";

const myObject = {
  position: {x: 0, y: 0: z: 0},
};

• With mutation

  const tween = spring(myObject.position);
  tween.to({x: 1, y: 2: z: 3});
  tween.update(1/60);

• With copy

  const tween = spring({...myObject.position});
  tween.to({x: 1, y: 2: z: 3});
  tween.update(1/60);
  Object.assign(myObject.position, tween.values);

API

Vector

Value container for all springs. Can have any number of dimensions.

type Vector = Record<string, number>;

Config

Three factors, stiffness, mass, and friction, control the behavior of a spring physics simulation.

The fourth config option, precision, determines how low velocity must be before the spring is considered settled. Once the spring is settled, it will set the spring value to the desired and pause simulation until a new desired value is supplied to the .to function.

const config = {
  stiffness: 25, // How strong is the spring
  mass: 10, // How heavy is the object
  friction: 5, // How thick is the medium the object travels in
  precision: 0.0005, // A threshold below which the spring settles and stops updating
};

const tween = spring({value: 0}, config);

Config is unit-less but values are related to time step used in update function.

For example, if your time step is in milliseconds instead of seconds, the config input must be set to numbers of a matching inverse magnitude.

To avoid the spring physics from going havoc, values must be low enough to achieve a negative feedback loop.

Spring Interface

values: Vector

Current state of simulation.

to(value: Vector): void

Set the desired state to which the spring will pull values.

set(value: Vector): void

Sets the value immediately and thus stops further updates.

update(deltaTime: number): void

Runs one cycle of the spring simulation moving the values toward their desired state. Fractions 1/10-1/120 is a reasonable range given the default spring config.

clear(): void

Stops updates immediately and put the values at rest

reconfigure(config: Config): void

Updates the spring physics config.