Claude-Code-Game-Studios/.claude/rules/engine-code.md

paths

paths
src/core/** Assets/**/{Core,core}/**/*.cs Source/**/{Core,core}/**/*.{h,cpp}

Engine Code Rules

• ZERO allocations in hot paths (update loops, rendering, physics) — pre-allocate, pool, reuse
• All engine APIs must be thread-safe OR explicitly documented as single-thread-only
• Profile before AND after every optimization — document the measured numbers
• Engine code must NEVER depend on gameplay code (strict dependency direction: engine <- gameplay)
• Every public API must have usage examples in its doc comment
• Changes to public interfaces require a deprecation period and migration guide
• Use RAII / deterministic cleanup for all resources
• All engine systems must support graceful degradation
• Before writing engine API code, consult docs/engine-reference/ for the current engine version and verify APIs against the reference docs

Examples

Correct (zero-alloc hot path) — Godot:

# Pre-allocated array reused each frame
var _nearby_cache: Array[Node3D] = []

func _physics_process(delta: float) -> void:
    _nearby_cache.clear()  # Reuse, don't reallocate
    _spatial_grid.query_radius(position, radius, _nearby_cache)

Unity:

private readonly Collider[] _nearbyCache = new Collider[64];  // allocated once

void FixedUpdate()
{
    int count = Physics.OverlapSphereNonAlloc(transform.position, radius, _nearbyCache);
}

Unreal:

// TArray member, reserved once; Reset() keeps the allocation
void UProximityComponent::TickComponent(float DeltaTime, ELevelTick TickType,
                                        FActorComponentTickFunction* ThisTickFunction)
{
    NearbyCache.Reset();
    SpatialGrid->QueryRadius(GetComponentLocation(), Radius, NearbyCache);
}

Incorrect (allocating in hot path):

func _physics_process(delta: float) -> void:
    var nearby: Array[Node3D] = []  # VIOLATION: allocates every frame
    nearby = get_tree().get_nodes_in_group("enemies")  # VIOLATION: tree query every frame