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const tinycolor = require('tinycolor2');
/**
* @typedef {Object} TinyGradient.StopInput
* @property {ColorInput} color
* @property {number} pos
*/
/**
* @typedef {Object} TinyGradient.StepValue
* @type {number} [r]
* @type {number} [g]
* @type {number} [b]
* @type {number} [h]
* @type {number} [s]
* @type {number} [v]
* @type {number} [a]
*/
/**
* @type {StepValue}
*/
const RGBA_MAX = { r: 256, g: 256, b: 256, a: 1 };
/**
* @type {StepValue}
*/
const HSVA_MAX = { h: 360, s: 1, v: 1, a: 1 };
/**
* Linearly compute the step size between start and end (not normalized)
* @param {StepValue} start
* @param {StepValue} end
* @param {number} steps - number of desired steps
* @return {StepValue}
*/
function stepize(start, end, steps) {
let step = {};
for (let k in start) {
if (start.hasOwnProperty(k)) {
step[k] = steps === 0 ? 0 : (end[k] - start[k]) / steps;
}
}
return step;
}
/**
* Compute the final step color
* @param {StepValue} step - from `stepize`
* @param {StepValue} start
* @param {number} i - color index
* @param {StepValue} max - rgba or hsva of maximum values for each channel
* @return {StepValue}
*/
function interpolate(step, start, i, max) {
let color = {};
for (let k in start) {
if (start.hasOwnProperty(k)) {
color[k] = step[k] * i + start[k];
color[k] = color[k] < 0 ? color[k] + max[k] : (max[k] !== 1 ? color[k] % max[k] : color[k]);
}
}
return color;
}
/**
* Generate gradient with RGBa interpolation
* @param {StopInput} stop1
* @param {StopInput} stop2
* @param {number} steps
* @return {tinycolor[]} color1 included, color2 excluded
*/
function interpolateRgb(stop1, stop2, steps) {
const start = stop1.color.toRgb();
const end = stop2.color.toRgb();
const step = stepize(start, end, steps);
let gradient = [stop1.color];
for (let i = 1; i < steps; i++) {
const color = interpolate(step, start, i, RGBA_MAX);
gradient.push(tinycolor(color));
}
return gradient;
}
/**
* Generate gradient with HSVa interpolation
* @param {StopInput} stop1
* @param {StopInput} stop2
* @param {number} steps
* @param {boolean|'long'|'short'} mode
* @return {tinycolor[]} color1 included, color2 excluded
*/
function interpolateHsv(stop1, stop2, steps, mode) {
const start = stop1.color.toHsv();
const end = stop2.color.toHsv();
// rgb interpolation if one of the steps in grayscale
if (start.s === 0 || end.s === 0) {
return interpolateRgb(stop1, stop2, steps);
}
let trigonometric;
if (typeof mode === 'boolean') {
trigonometric = mode;
}
else {
const trigShortest = (start.h < end.h && end.h - start.h < 180) || (start.h > end.h && start.h - end.h > 180);
trigonometric = (mode === 'long' && trigShortest) || (mode === 'short' && !trigShortest);
}
const step = stepize(start, end, steps);
let gradient = [stop1.color];
// recompute hue
let diff;
if ((start.h <= end.h && !trigonometric) || (start.h >= end.h && trigonometric)) {
diff = end.h - start.h;
}
else if (trigonometric) {
diff = 360 - end.h + start.h;
}
else {
diff = 360 - start.h + end.h;
}
step.h = Math.pow(-1, trigonometric ? 1 : 0) * Math.abs(diff) / steps;
for (let i = 1; i < steps; i++) {
const color = interpolate(step, start, i, HSVA_MAX);
gradient.push(tinycolor(color));
}
return gradient;
}
/**
* Compute substeps between each stops
* @param {StopInput[]} stops
* @param {number} steps
* @return {number[]}
*/
function computeSubsteps(stops, steps) {
const l = stops.length;
// validation
steps = parseInt(steps, 10);
if (isNaN(steps) || steps < 2) {
throw new Error('Invalid number of steps (< 2)');
}
if (steps < l) {
throw new Error('Number of steps cannot be inferior to number of stops');
}
// compute substeps from stop positions
let substeps = [];
for (let i = 1; i < l; i++) {
const step = (steps - 1) * (stops[i].pos - stops[i - 1].pos);
substeps.push(Math.max(1, Math.round(step)));
}
// adjust number of steps
let totalSubsteps = 1;
for (let n = l - 1; n--;) totalSubsteps += substeps[n];
while (totalSubsteps !== steps) {
if (totalSubsteps < steps) {
const min = Math.min.apply(null, substeps);
substeps[substeps.indexOf(min)]++;
totalSubsteps++;
}
else {
const max = Math.max.apply(null, substeps);
substeps[substeps.indexOf(max)]--;
totalSubsteps--;
}
}
return substeps;
}
/**
* Compute the color at a specific position
* @param {StopInput[]} stops
* @param {number} pos
* @param {string} method
* @param {StepValue} max
* @returns {tinycolor}
*/
function computeAt(stops, pos, method, max) {
if (pos < 0 || pos > 1) {
throw new Error('Position must be between 0 and 1');
}
let start, end;
for (let i = 0, l = stops.length; i < l - 1; i++) {
if (pos >= stops[i].pos && pos < stops[i + 1].pos) {
start = stops[i];
end = stops[i + 1];
break;
}
}
if (!start) {
start = end = stops[stops.length - 1];
}
const step = stepize(start.color[method](), end.color[method](), (end.pos - start.pos) * 100);
const color = interpolate(step, start.color[method](), (pos - start.pos) * 100, max);
return tinycolor(color);
}
class TinyGradient {
/**
* @param {StopInput[]|ColorInput[]} stops
* @returns {TinyGradient}
*/
constructor(stops) {
// validation
if (stops.length < 2) {
throw new Error('Invalid number of stops (< 2)');
}
const havingPositions = stops[0].pos !== undefined;
let l = stops.length;
let p = -1;
let lastColorLess = false;
// create tinycolor objects and clean positions
this.stops = stops.map((stop, i) => {
const hasPosition = stop.pos !== undefined;
if (havingPositions ^ hasPosition) {
throw new Error('Cannot mix positionned and not posionned color stops');
}
if (hasPosition) {
const hasColor = stop.color !== undefined;
if (!hasColor && (lastColorLess || i === 0 || i === l - 1)) {
throw new Error('Cannot define two consecutive position-only stops');
}
lastColorLess = !hasColor;
stop = {
color : hasColor ? tinycolor(stop.color) : null,
colorLess: !hasColor,
pos : stop.pos
};
if (stop.pos < 0 || stop.pos > 1) {
throw new Error('Color stops positions must be between 0 and 1');
}
else if (stop.pos < p) {
throw new Error('Color stops positions are not ordered');
}
p = stop.pos;
}
else {
stop = {
color: tinycolor(stop.color !== undefined ? stop.color : stop),
pos : i / (l - 1)
};
}
return stop;
});
if (this.stops[0].pos !== 0) {
this.stops.unshift({
color: this.stops[0].color,
pos : 0
});
l++;
}
if (this.stops[l - 1].pos !== 1) {
this.stops.push({
color: this.stops[l - 1].color,
pos : 1
});
}
}
/**
* Return new instance with reversed stops
* @return {TinyGradient}
*/
reverse() {
let stops = [];
this.stops.forEach(function (stop) {
stops.push({
color: stop.color,
pos : 1 - stop.pos
});
});
return new TinyGradient(stops.reverse());
}
/**
* Return new instance with looped stops
* @return {TinyGradient}
*/
loop() {
let stops1 = [];
let stops2 = [];
this.stops.forEach((stop) => {
stops1.push({
color: stop.color,
pos : stop.pos / 2
});
});
this.stops.slice(0, -1).forEach((stop) => {
stops2.push({
color: stop.color,
pos : 1 - stop.pos / 2
});
});
return new TinyGradient(stops1.concat(stops2.reverse()));
}
/**
* Generate gradient with RGBa interpolation
* @param {number} steps
* @return {tinycolor[]}
*/
rgb(steps) {
const substeps = computeSubsteps(this.stops, steps);
let gradient = [];
this.stops.forEach((stop, i) => {
if (stop.colorLess) {
stop.color = interpolateRgb(this.stops[i - 1], this.stops[i + 1], 2)[1];
}
});
for (let i = 0, l = this.stops.length; i < l - 1; i++) {
const rgb = interpolateRgb(this.stops[i], this.stops[i + 1], substeps[i]);
gradient.splice(gradient.length, 0, ...rgb);
}
gradient.push(this.stops[this.stops.length - 1].color);
return gradient;
}
/**
* Generate gradient with HSVa interpolation
* @param {number} steps
* @param {boolean|'long'|'short'} [mode=false]
* - false to step in clockwise
* - true to step in trigonometric order
* - 'short' to use the shortest way
* - 'long' to use the longest way
* @return {tinycolor[]}
*/
hsv(steps, mode) {
const substeps = computeSubsteps(this.stops, steps);
let gradient = [];
this.stops.forEach((stop, i) => {
if (stop.colorLess) {
stop.color = interpolateHsv(this.stops[i - 1], this.stops[i + 1], 2, mode)[1];
}
});
for (let i = 0, l = this.stops.length; i < l - 1; i++) {
const hsv = interpolateHsv(this.stops[i], this.stops[i + 1], substeps[i], mode);
gradient.splice(gradient.length, 0, ...hsv);
}
gradient.push(this.stops[this.stops.length - 1].color);
return gradient;
}
/**
* Generate CSS3 command (no prefix) for this gradient
* @param {String} [mode=linear] - 'linear' or 'radial'
* @param {String} [direction] - default is 'to right' or 'ellipse at center'
* @return {String}
*/
css(mode, direction) {
mode = mode || 'linear';
direction = direction || (mode === 'linear' ? 'to right' : 'ellipse at center');
let css = mode + '-gradient(' + direction;
this.stops.forEach(function (stop) {
css += ', ' + (stop.colorLess ? '' : stop.color.toRgbString() + ' ') + (stop.pos * 100) + '%';
});
css += ')';
return css;
}
/**
* Returns the color at specific position with RGBa interpolation
* @param {number} pos, between 0 and 1
* @return {tinycolor}
*/
rgbAt(pos) {
return computeAt(this.stops, pos, 'toRgb', RGBA_MAX);
}
/**
* Returns the color at specific position with HSVa interpolation
* @param {number} pos, between 0 and 1
* @return {tinycolor}
*/
hsvAt(pos) {
return computeAt(this.stops, pos, 'toHsv', HSVA_MAX);
}
}
/**
* @param {StopInput[]|ColorInput[]|StopInput...|ColorInput...} stops
* @returns {TinyGradient}
*/
module.exports = function (stops) {
// varargs
if (arguments.length === 1) {
if (!Array.isArray(arguments[0])) {
throw new Error('"stops" is not an array');
}
stops = arguments[0];
}
else {
stops = Array.prototype.slice.call(arguments);
}
return new TinyGradient(stops);
};