src/js/quaternion.js

export class Quaternion {
    constructor(x = 0, y = 0, z = 0, w = 1) {
        this.x = x;
        this.y = y;
        this.z = z;
        this.w = w;
    }

    static fromEuler(x, y, z) {
        const cx = Math.cos(x * 0.5);
        const cy = Math.cos(y * 0.5);
        const cz = Math.cos(z * 0.5);
        const sx = Math.sin(x * 0.5);
        const sy = Math.sin(y * 0.5);
        const sz = Math.sin(z * 0.5);

        return new Quaternion(
            sx * cy * cz + cx * sy * sz,
            cx * sy * cz - sx * cy * sz,
            cx * cy * sz + sx * sy * cz,
            cx * cy * cz - sx * sy * sz
        );
    }

    static multiply(a, b) {
        return new Quaternion(
            a.w * b.x + a.x * b.w + a.y * b.z - a.z * b.y,
            a.w * b.y - a.x * b.z + a.y * b.w + a.z * b.x,
            a.w * b.z + a.x * b.y - a.y * b.x + a.z * b.w,
            a.w * b.w - a.x * b.x - a.y * b.y - a.z * b.z
        );
    }

    normalize() {
        const len = Math.sqrt(
            this.x * this.x +
            this.y * this.y +
            this.z * this.z +
            this.w * this.w
        );
        if (len === 0) return this;
        const invLen = 1 / len;
        return new Quaternion(
            this.x * invLen,
            this.y * invLen,
            this.z * invLen,
            this.w * invLen
        );
    }

    clone() {
        return new Quaternion(this.x, this.y, this.z, this.w);
    }
}