Use this skill when implementing game programming patterns - state machines for character/AI behavior, object pooling for performance-critical spawning, event systems for decoupled game communication, or the command pattern for input handling, undo/redo, and replays. Triggers on game architecture, game loop design, entity management, finite state machines, object pools, observer/event bus, command queues, and gameplay programming patterns.
Use this skill when implementing game programming patterns - state machines for character/AI behavior, object pooling for performance-critical spawning, event systems for decoupled game communication, or the command pattern for input handling, undo/redo, and replays. Triggers on game architecture, game loop design, entity management, finite state machines, object pools, observer/event bus, command queues, and gameplay programming patterns.
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Game Design Patterns
Game design patterns solve recurring problems in game development where standard
enterprise patterns fall short. Games face unique constraints: real-time frame budgets
(16ms at 60fps), thousands of dynamic entities, complex state transitions for AI and
player characters, and the need for deterministic replay and undo. This skill covers
four foundational patterns - state machines, object pooling, event systems, and the
command pattern - that form the backbone of well-architected gameplay code.
When to use this skill
Trigger this skill when the user:
Needs to model character states, AI behavior, or game phases with a state machine
Wants to implement object pooling for bullets, particles, enemies, or other frequently spawned entities
Asks about event systems, message buses, or observer patterns in a game context
Needs the command pattern for input handling, undo/redo, or action replays
Is building a game loop and needs architectural guidance on entity management
Wants to decouple game systems (audio, UI, physics) from gameplay logic
Asks about managing game state transitions (menus, gameplay, pause, cutscenes)
Do NOT trigger this skill for:
Rendering, shaders, or graphics programming (not a design pattern concern)
General software design patterns unrelated to games (use clean-architecture instead)
Key principles
Frame budget is law - Every pattern choice must respect the ~16ms frame budget.
Allocations during gameplay cause GC spikes. Indirection has cache costs. Always
profile before adding abstraction.
Decouple, but not infinitely - Game systems should communicate through events
and commands rather than direct references, but over-decoupling creates debugging
nightmares. One level of indirection is usually enough.
State is explicit - Implicit state (nested boolean flags, mode integers) leads
to impossible combinations and subtle bugs. Make every valid state a first-class
object with defined transitions.
Pool what you spawn - Any entity created and destroyed more than once per
second should be pooled. The cost of allocation is not the constructor - it is the
garbage collector pause 3 seconds later.
Commands are data - When input actions are objects rather than direct method
calls, you get undo, replay, networking, and AI "for free." The command pattern
is the single highest-leverage pattern in gameplay code.
Core concepts
State machines model entities that have distinct behavioral modes. A character
can be Idle, Running, Jumping, or Attacking - but never Jumping and Idle at the same
time. Each state encapsulates its own update logic, entry/exit behavior, and valid
transitions. Hierarchical state machines (HFSM) add nested sub-states for complex AI.
Object pooling pre-allocates a fixed set of objects and recycles them instead of
creating and destroying instances at runtime. The pool maintains an "available" list
and hands out pre-initialized objects on request, reclaiming them when they are
"killed." This eliminates allocation pressure during gameplay.
Event systems (also called observer, pub/sub, or message bus) let game systems
communicate without direct references. When a player takes damage, the health system
fires a DamageTaken event. The UI, audio, camera shake, and analytics systems each
subscribe independently. Adding a new reaction requires zero changes to the damage code.
The command pattern encapsulates an action as an object with execute() and
optionally undo(). Player input becomes a stream of command objects. This enables
input rebinding, replay recording, undo/redo in editors, and sending commands over
the network for multiplayer.
Common tasks
Implement a finite state machine for character behavior
Each state is a class with enter(), update(), exit(), and a transition check.
The machine holds the current state and delegates to it.
Size the pool to your worst-case burst. If acquire() returns null, either grow
the pool (with a warning log) or skip the spawn - never allocate inline.
Set up a typed event system
Use a type-safe event bus so subscribers know exactly what payload to expect.
Deterministic lockstep requires all clients to process the exact same commands
in the exact same frame order. Floating-point differences across platforms
will cause desync - use fixed-point math for critical state.
new Bullet() every frame causes GC pauses and frame drops
Pool all frequently spawned objects
God event bus
Every system subscribes to everything on one global bus
Scope buses per domain (combat bus, UI bus) or use direct listeners for tight couplings
Commands without undo
Implementing execute() but skipping undo() for "simplicity"
Always implement undo() even if unused now - replay and debugging need it
Stringly-typed events
Using raw strings like "dmg" instead of typed event names
Use a typed EventMap (TypeScript) or enum-based keys so typos are compile errors
Unbounded command history
Storing every command forever leaks memory in long sessions
Cap history length or checkpoint + truncate periodically
Spaghetti transitions
Every state can transition to every other state
Define a transition table upfront. If a transition is not in the table, it is illegal
Gotchas
Object pools sized for average load, not burst load, cause missed spawns - If you size a bullet pool for "average 50 bullets" but the boss fight fires 200 in 2 seconds, acquire() returns null and bullets silently fail to spawn. Always size pools to the worst-case burst in your game, add pool expansion with a warning log, and test the burst scenario explicitly.
State machine transitions that allocate new State objects cause GC pressure - If each transition() call does new JumpState(character), you're allocating during gameplay, which triggers garbage collection pauses. Pre-allocate all state instances at startup and store them in a dictionary; transition by swapping references, not by creating new objects.
Event bus subscriptions from destroyed entities cause null reference crashes - When a game object is destroyed without unsubscribing its event handlers, the next event dispatch calls a handler with a null this context and crashes or produces stale state. Always store and invoke the unsubscribe function returned by on() in the entity's destroy/cleanup path.
Command history grows unbounded in long sessions - Storing every command since session start for an undo system will consume growing memory over hours of gameplay. Cap the command history to a maximum depth (e.g., 100 commands) or checkpoint-and-truncate periodically. For replay systems, commands older than the checkpoint can be dropped.
Deterministic lockstep breaks silently on floating-point operations - Two clients running the same command stream will desync if any physics or movement calculation uses floating-point math, because IEEE 754 results can differ across CPU architectures and compiler optimizations. Use fixed-point arithmetic for all game state that must be deterministic across clients.
References
For detailed content on specific patterns, read the relevant file from references/:
references/state-machines.md - Hierarchical FSMs, pushdown automata, behavior tree comparison, and transition table design
references/object-pooling.md - Pool sizing strategies, warm-up patterns, thread safety, and language-specific GC considerations
references/event-systems.md - Event queue vs immediate dispatch, priority ordering, event filtering, and debugging leaked subscriptions
references/command-pattern.md - Serialization for replay/networking, macro recording, composite commands, and undo stack management
Only load a references file if the current task requires deep detail on that topic.
Companion check
On first activation of this skill in a conversation: check which companion skills are installed by running ls ~/.claude/skills/ ~/.agent/skills/ ~/.agents/skills/ .claude/skills/ .agent/skills/ .agents/skills/ 2>/dev/null. Compare the results against the recommended_skills field in this file's frontmatter. For any that are missing, mention them once and offer to install:
