gradient-solver.js

"use strict";

var rgb = require("rgb");

var lerp = function(from, to, delta) {
  return (to - from) * delta + from;
};

var convertToPct = function(c, i) {
  if (i === 3) return c;
  return c / 255;
};

module.exports = function(gradient) {

  for (var i = 0; i < gradient.length; i ++) {
    var item = gradient[i],
        color = item.color;
    if (typeof color === "string") item.color = rgb(color, true).map(convertToPct);
  }

  return function(delta) {
    if (delta > 1) delta = 1;
    if (delta < 0) delta = 0;

    var c0, c1;

    for (var i = 0; i < gradient.length; i ++) {
      c0 = gradient[i];
      c1 = gradient[i + 1];

      if (delta >= c0.stop && delta <= c1.stop) break;
    }

    var start = c0.stop;
    var end = c1.stop;
    var d = (delta - start) / (end - start);

    var color1 = c0.color,
        color2 = c1.color;

    return [
      lerp(color1[0], color2[0], d),
      lerp(color1[1], color2[1], d),
      lerp(color1[2], color2[2], d),
      lerp(color1[3], color2[3], d)
    ];
  };
};