vector.js

class Vec4 {

    constructor(x, y, z, w) {
        this.x = x;
        this.y = y;
        this.z = z;
        this.w = w ?? 0;
    }

    scaled(by) {
        return new Vec4(this.x * by, this.y * by, this.z * by, this.w * by);
    }

    dot(other) {
        return this.x * other.x +
            this.y * other.y +
            this.z * other.z +
            this.w * other.w;
    }

    length() {
        return Math.sqrt(this.x * this.x + this.y * this.y + this.z * this.z + this.w * this.w);
    }

    norm() {
        let len = this.length();

        return new Vec4(this.x / len, this.y / len, this.z / len, this.w / len);
    }

    add(other) {
        return new Vec4(this.x + other.x, this.y + other.y, this.z + other.z, this.w + other.w);
    }

    sub(other) {
        return this.add(other.scaled(-1));
    }

    cross(other) {
        let x = this.y * other.z - this.z * other.y;
        let y = this.z * other.x - this.x * other.z;
        let z = this.x * other.y - this.y * other.x;

        return new Vec4(x, y, z, 0);
    }

    /**
     * Calculate the normal of the given triangle. 
     * For the resulting normal to point in the positive y direction, p0 to p1 should be to the 
     * left of p0 to p2
     * @param {Vec4} p0 
     * @param {Vec4} p1 
     * @param {Vec4} p2 
     * @returns Vec4
     */
    static normal_of_triangle(p0, p1, p2) {
        let v0 = p1.sub(p0);
        let v1 = p2.sub(p0);
        return v0.cross(v1);
    }

    toString() {
        return ['[', this.x, this.y, this.z, this.w, ']'].join(' ');
    }
}