@woosh/meep-engine/src/engine/network/adapters/QuaternionInterpolationAdapter.js

Pure JavaScript game engine. Fully featured and production ready.

import { BinaryInterpolationAdapter } from "../sim/BinaryInterpolationAdapter.js";

/**
 * Shortest-path nlerp for a 4 × Float32 quaternion payload (16 bytes).
 * Switch to a slerp variant if you need it for wide per-tick angular
 * steps (animation-blended joints, slow snapshot rate).
 *
 * @author Alex Goldring
 * @copyright Company Named Limited (c) 2025
 */
export class QuaternionInterpolationAdapter extends BinaryInterpolationAdapter {

    /** @inheritdoc */
    interpolate(out_buffer, source, first_offset, second_offset, t) {
        source.position = first_offset;
        const ax = source.readFloat32();
        const ay = source.readFloat32();
        const az = source.readFloat32();
        const aw = source.readFloat32();

        source.position = second_offset;
        let bx = source.readFloat32();
        let by = source.readFloat32();
        let bz = source.readFloat32();
        let bw = source.readFloat32();

        if (ax * bx + ay * by + az * bz + aw * bw < 0) {
            bx = -bx; by = -by; bz = -bz; bw = -bw;
        }

        let qx = ax + (bx - ax) * t;
        let qy = ay + (by - ay) * t;
        let qz = az + (bz - az) * t;
        let qw = aw + (bw - aw) * t;

        const len2 = qx * qx + qy * qy + qz * qz + qw * qw;
        const inv_len = len2 > 0 ? 1 / Math.sqrt(len2) : 1;

        out_buffer.writeFloat32(qx * inv_len);
        out_buffer.writeFloat32(qy * inv_len);
        out_buffer.writeFloat32(qz * inv_len);
        out_buffer.writeFloat32(qw * inv_len);
    }
}