Add ViewingConditions parameter to Hct.from

[nvlang]

Introduction

I'm using the TypeScript version of the library, and as far as I can tell, the only way to specify an HCT color with a hue-chroma-tone triplet is as follows:

let color = Hct.from(10, 20, 30);
console.log(color.inViewingConditions(ViewingConditions.DEFAULT).hue);    // 9.78535871122963
console.log(color.inViewingConditions(ViewingConditions.DEFAULT).chroma); // 20.066003985753465
console.log(color.inViewingConditions(ViewingConditions.DEFAULT).tone);   // 30.089123886290032

In other words, Hct.from creates an Hct object which, in default viewing conditions, has the specified hue, chroma, and tone — or, values that are as close to the specified ones as possible. No surprise there, it's mentioned in the method's documentation.

Problem

Now, I was trying to create a color palette for a specific set of viewing conditions, e.g.:

let vc = ViewingConditions.make(undefined, undefined, 10, undefined, undefined)

(Here, vc would correspond to the default viewing conditions except with the background L* set to 10 instead of the default of 50) (i.e., a darker background).

I want the colors in my palette to appear consistent in tone and chroma for these viewing conditions, not the default viewing conditions.

let color1 = Hct.from(60,10,20);
let color2 = Hct.from(280,10,20);
console.log(color1.inViewingConditions(vc).hue);    // 60 vs 58.82148886264458
console.log(color2.inViewingConditions(vc).hue);    // 280 vs 282.2639993051888
console.log(color1.inViewingConditions(vc).chroma); // 10 vs 5.977109516590248
console.log(color2.inViewingConditions(vc).chroma); // 10 vs 6.3614473636394
console.log(color1.inViewingConditions(vc).tone);   // 20 vs 12.489930368768537
console.log(color2.inViewingConditions(vc).tone);   // 20 vs 12.480603303269618

As can be seen in the above example, this desired consistency is not guaranteed if the colors are defined with Hct.from. As a matter of fact, I don't know of any way to guarantee this consistency.

Suggestion

I would suggest adding an additional optional parameter to the Hct.from:

export declare class Hct {
    // ...
    static from(hue: number, chroma: number, tone: number, viewingConditions: ViewingConditions): Hct;
}

The color could still be stored internally as the hue-chroma-tone triplet from the default viewing conditions, of course.