s2maps-gpu/dist/style/easingFunctions.js

S2 Maps GPU - An open source, high-performance, and GPU-accelerated map engine for rendering large-scale, interactive maps.

import { Color, interpolate } from './color/index.js';
/**
 * Convert a string to a function that will return an interpolation
 * between two values or colors.
 * @param easeType - ease type
 * @param base - base value
 * @returns an easing function
 */
export default function getEasingFunction(easeType = 'lin', base = 1) {
    const func = easeType === 'lin'
        ? linear
        : easeType === 'expo'
            ? exponential
            : easeType === 'quad'
                ? quad
                : easeType === 'cubic'
                    ? cubic
                    : step;
    return (zoom, start, end, startValue, endValue) => {
        const t = func(zoom, start, end, base);
        if (typeof startValue === 'number' && typeof endValue === 'number')
            return (startValue + t * (endValue - startValue));
        else if (startValue instanceof Color && endValue instanceof Color)
            return interpolate(startValue, endValue, t);
        else
            return startValue;
    };
}
/**
 * Linear ease function: y = mx
 * @param input - input value
 * @param start - start value
 * @param end - end value
 * @returns the interpolated value
 */
function linear(input, start, end) {
    return (input - start) / (end - start);
}
/**
 * Exponential ease function: y = e^x OR y = Math.pow(2, 10 * x)
 * @param input - input value
 * @param start - start value
 * @param end - end value
 * @param base - base value
 * @returns the interpolated value
 */
function exponential(input, start, end, base) {
    // grab change
    const diff = end - start;
    if (diff === 0)
        return 0;
    // refine base value
    if (base <= 0)
        base = 0.1;
    else if (base > 2)
        base = 2;
    // grab diff
    const progress = input - start;
    // linear case
    if (base === 1)
        return progress / diff;
    // solve
    return (Math.pow(base, progress) - 1) / (Math.pow(base, diff) - 1);
}
/**
 * Quadratic ease function: y = x^2
 * @param input - input value
 * @param start - start value
 * @param end - end value
 * @returns the interpolated value
 */
function quad(input, start, end) {
    return Math.pow(input - start, 2) / Math.pow(end - start, 2);
}
/**
 * Cubic ease function: y = x^3
 * @param input - input value
 * @param start - start value
 * @param end - end value
 * @returns the interpolated value
 */
function cubic(input, start, end) {
    return Math.pow(input - start, 3) / Math.pow(end - start, 3);
}
/**
 * Stepping ease function: y = 1 or 0
 * @param input - input value
 * @param _start - start value
 * @param end - end value
 * @returns the interpolated value
 */
function step(input, _start, end) {
    return input >= end ? 1 : 0;
}