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/** @import { SpringOpts, SpringUpdateOpts, TickContext } from './private.js' */
/** @import { Spring } from './public.js' */
import { writable } from '../store/shared/index.js';
import { loop } from '../internal/client/loop.js';
import { raf } from '../internal/client/timing.js';
import { is_date } from './utils.js';
/**
* @template T
* @param {TickContext<T>} ctx
* @param {T} last_value
* @param {T} current_value
* @param {T} target_value
* @returns {T}
*/
function tick_spring(ctx, last_value, current_value, target_value) {
if (typeof current_value === 'number' || is_date(current_value)) {
// @ts-ignore
const delta = target_value - current_value;
// @ts-ignore
const velocity = (current_value - last_value) / (ctx.dt || 1 / 60); // guard div by 0
const spring = ctx.opts.stiffness * delta;
const damper = ctx.opts.damping * velocity;
const acceleration = (spring - damper) * ctx.inv_mass;
const d = (velocity + acceleration) * ctx.dt;
if (Math.abs(d) < ctx.opts.precision && Math.abs(delta) < ctx.opts.precision) {
return target_value; // settled
} else {
ctx.settled = false; // signal loop to keep ticking
// @ts-ignore
return is_date(current_value) ? new Date(current_value.getTime() + d) : current_value + d;
}
} else if (Array.isArray(current_value)) {
// @ts-ignore
return current_value.map((_, i) =>
// @ts-ignore
tick_spring(ctx, last_value[i], current_value[i], target_value[i])
);
} else if (typeof current_value === 'object') {
const next_value = {};
for (const k in current_value) {
// @ts-ignore
next_value[k] = tick_spring(ctx, last_value[k], current_value[k], target_value[k]);
}
// @ts-ignore
return next_value;
} else {
throw new Error(`Cannot spring ${typeof current_value} values`);
}
}
/**
* The spring function in Svelte creates a store whose value is animated, with a motion that simulates the behavior of a spring. This means when the value changes, instead of transitioning at a steady rate, it "bounces" like a spring would, depending on the physics parameters provided. This adds a level of realism to the transitions and can enhance the user experience.
*
* @template [T=any]
* @param {T} [value]
* @param {SpringOpts} [opts]
* @returns {Spring<T>}
*/
export function spring(value, opts = {}) {
const store = writable(value);
const { stiffness = 0.15, damping = 0.8, precision = 0.01 } = opts;
/** @type {number} */
let last_time;
/** @type {Task | null} */
let task;
/** @type {object} */
let current_token;
let last_value = /** @type {T} */ (value);
let target_value = /** @type {T | undefined} */ (value);
let inv_mass = 1;
let inv_mass_recovery_rate = 0;
let cancel_task = false;
/**
* @param {T} new_value
* @param {SpringUpdateOpts} opts
* @returns {Promise<void>}
*/
function set(new_value, opts = {}) {
target_value = new_value;
const token = (current_token = {});
if (value == null || opts.hard || (spring.stiffness >= 1 && spring.damping >= 1)) {
cancel_task = true; // cancel any running animation
last_time = raf.now();
last_value = new_value;
store.set((value = target_value));
return Promise.resolve();
} else if (opts.soft) {
const rate = opts.soft === true ? 0.5 : +opts.soft;
inv_mass_recovery_rate = 1 / (rate * 60);
inv_mass = 0; // infinite mass, unaffected by spring forces
}
if (!task) {
last_time = raf.now();
cancel_task = false;
task = loop((now) => {
if (cancel_task) {
cancel_task = false;
task = null;
return false;
}
inv_mass = Math.min(inv_mass + inv_mass_recovery_rate, 1);
/** @type {TickContext<T>} */
const ctx = {
inv_mass,
opts: spring,
settled: true,
dt: ((now - last_time) * 60) / 1000
};
// @ts-ignore
const next_value = tick_spring(ctx, last_value, value, target_value);
last_time = now;
last_value = /** @type {T} */ (value);
store.set((value = /** @type {T} */ (next_value)));
if (ctx.settled) {
task = null;
}
return !ctx.settled;
});
}
return new Promise((fulfil) => {
/** @type {Task} */ (task).promise.then(() => {
if (token === current_token) fulfil();
});
});
}
/** @type {Spring<T>} */
const spring = {
set,
update: (fn, opts) => set(fn(/** @type {T} */ (target_value), /** @type {T} */ (value)), opts),
subscribe: store.subscribe,
stiffness,
damping,
precision
};
return spring;
}
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