Project-M/Assets/_Project/Scripts/Simulation/FacingMath.cs

using Unity.Mathematics;

namespace ProjectM.Simulation
{
    /// <summary>
    /// Pure facing/aim math for the Shape-of-Dreams facing model (body yaw follows movement; turns toward
    /// the aim only inside a cast window; holds when idle; the cursor is never passively tracked).
    /// RotateToward is the verbatim extraction of PlayerAimSystem's rate-limited planar turn so it stays
    /// the tested-in-play math. ResolveAim is THE gameplay fire-direction resolver — every damage/spawn
    /// direction (AbilityFireSystem archetypes, MeleeComboSystem cleave) and the aim-readout presentation
    /// (reticle, local slash arcs) must route through it so sim and FX can never diverge. EditMode-tested,
    /// Burst-safe, no World needed.
    /// </summary>
    public static class FacingMath
    {
        /// <summary>Gameplay fire direction: raw replicated Aim when meaningful, else the current body facing
        /// (resting gamepad right stick — preserves controller-first "zero aim = movement heading" because
        /// facing tracks Move under the SoD model), else world +Z. Always normalized.</summary>
        public static float2 ResolveAim(float2 aim, float2 facing)
        {
            if (math.lengthsq(aim) > 1e-6f) return math.normalize(aim);
            if (math.lengthsq(facing) > 1e-6f) return math.normalize(facing);
            return new float2(0f, 1f);
        }

        /// <summary>The shared Aim→Move→hold cascade. castActive grants Aim PRIORITY only — a zero Aim
        /// (resting gamepad stick mid-cast) falls through to Move, then to "no target" (hold previous
        /// facing). Returns false when there is no target this tick.</summary>
        public static bool SelectTarget(bool castActive, float2 aim, float2 move, out float2 target)
        {
            if (castActive && math.lengthsq(aim) > 1e-6f)
            {
                target = math.normalize(aim);
                return true;
            }
            if (math.lengthsq(move) > 1e-6f)
            {
                target = math.normalize(move);
                return true;
            }
            target = default;
            return false;
        }

        /// <summary>Rate-limited planar rotate toward a normalized target: snaps when uninitialized or within
        /// reach this step, else rotates by maxStepRadians toward the target. Deterministic pure math
        /// (fixed-step dt at the caller) so it replays identically on rollback re-simulation.</summary>
        public static float2 RotateToward(float2 current, float2 target, float maxStepRadians)
        {
            if (math.lengthsq(current) < 1e-6f)
                return target; // uninitialized facing -> snap to target

            float2 cur = math.normalize(current);
            float angle = math.acos(math.clamp(math.dot(cur, target), -1f, 1f));
            if (angle <= maxStepRadians)
                return target; // within reach this step

            float sign = (cur.x * target.y - cur.y * target.x) >= 0f ? 1f : -1f;
            math.sincos(maxStepRadians * sign, out float sn, out float cs);
            return math.normalize(new float2(cur.x * cs - cur.y * sn, cur.x * sn + cur.y * cs));
        }
    }
}