Managing Game State And Resources Efficiently In The Game Loop

Optimizing Resource Usage in the Game Loop

The game loop is at the core of every game engine and manages updating the game state, processing user input, running game logic, rendering graphics, and other vital tasks. As the central component that all gameplay code relies on, optimizing resource usage in the game loop is critical for performance.

Common resources that need careful management in the loop include memory allocations, garbage collection, object pools, scene graphs, and cache systems. By reducing unnecessary memory traffic and reuse, games can achieve higher, more consistent frame rates and reduce hitches during gameplay.

Reducing Memory Allocations

Frequent memory allocations and deallocations can trigger garbage collection pauses, which pause the game to cleanup unused memory. This causes visible stutters and lag during gameplay. By reusing memory and reducing new allocations, games can avoid excessive garbage collection.

Strategies to minimize allocations include:

• Reusing common game objects via object pooling instead of frequently instantiating/destroying them.
• Preallocating reusable containers and memory blocks during loading instead of allocating per-frame.
• Avoiding hidden allocations inside game logic code paths that run each frame.
• Profiling memory usage to identity unnecessary allocations.

Reusing Objects with Object Pools

Object pools are a common technique that stores a collection of reusable game object instances that can be retrieved as needed instead of instantiated and later destroyed.

By reusing the same objects, memory allocation is minimized. This applies to objects like bullets, particle effects, enemies, and more that are commonly spawned and removed throughout gameplay.

Implementing an object pool requires:

• An abstract base class definining common methods like OnSpawn() and OnDespawn().
• Subclasses overriding those methods for each poolable object type.
• The pool class itself which stores inactive objects and returns active ones.
• Game logic to get/return objects from the pools instead of creating/destroying.

Properly tuned object pools can dramatically cut memory allocations in gameplay code.

Limiting Garbage Collection with Caches

For data that cannot be easily pooled, caching can be used to reuse objects without allocations. This requires specifically keeping references to objects over multiple frames rather than allowing out-of-scope destruction.

Examples include caching things like:

• Results of expensive calculations across frames.
• Frequently reused textures/materials.
• GameObject and component lookups in the scene graph.
• Results of physics collisions and raycasts.

Caching only works if code ensures cached objects are removed on level changes or other context switches. Otherwise, caches grow unlimited and are never garbage collected.

Managing Scene Graphs for Efficient Rendering

The scene graph is the logical structure of GameObjects, components, and other objects that makeup a game scene or level. Efficiently managing this graph is key for fast rendering.

Guidelines include:

• Minimizing draw calls by reducing GameObjects with unique meshes/materials.
• Batching objects into larger containers with combined materials.
• Disabling non-visible objects from rendering dynamically.
• Organizing object hierarchy spatially for better culling.
• Making static levels fully static to skip per-frame overhead.

Most game engines provide profiling tools to analyze draw calls, batches, triangle/vertex counts to optimize further.

Processing Input Events Efficiently

User input typically involves events like key presses, button clicks, touch taps, controller input, and mouse movement. Processing these properly is vital for responsive controls.

Tips for efficient input handling include:

• Avoid running logic immediately on low-level input events.
• Buffer events into intermediate data structures first.
• Process buffered events just once per frame.
• Rate limit events like mouse movement for smoother handling.
• Favor fewer callbacks on mono behaviours over polling states.

The intermediate buffering step helps batch process input events together rather than individually. This improves performance dramatically compared to naively handling immediately.

Updating Game State Optimally

The game state encompasses all aspects of the current gameplay world like entity positions, health, animations as well as game rules, progression tracking, and session data.

Guidelines for efficiently updating state include:

• Structuring state to minimize cache misses during update.
• Applying state changes just once based on a consistent global order.
• Updating only states that actually changed from last frame.
• Partitioning state updates by frequency (i.e. physics at fixed rate).

Updating states randomly or multiple times per frame should be avoided. Apply changes linearly in a structured fashion.

Strategies for Timestepping and Interpolation

Game state is inherently tied to time. But frame rates can fluctuate for many reasons introducing variance into game durations.

Engine mechanisms help address this including:

• Fixed timestepping – Updating logic at a constant timestep decoupled from render rate.
• Interpolation – Smoothly blending animated states between discrete game updates.
• Lag compensation – Adjusting game elements to account for input/network latency.

These strategies prevent visual glitches and keep the gameplay behavior consistent regardless of frame rate changes.

Examples in Unity and Unreal Engine

The most popular game engines provide many performance optimization features out-of-the-box. But also allow customization if developers need more control.

Unity

Key Unity features for optimization include:

• C# job system – Parallelize game code across threads.
• C# burst compiler – Generate optimized native code.
• DOTS/ECS – Data-oriented tech stack as an alternative to GameObjects.
• Hybrid renderer – Batching and instancing for faster rendering.
• Profiler – In-depth analysis of CPU/GPU usage.

Unity gives full control over the game loop, allowing frame rate independence and custom fixed timestepping.

Unreal Engine

Key Unreal Engine features include:

• Blueprints – Visual scripting for faster iteration.
• Niagara – Optimized particle simulation and rendering.
• World partitioning – Occlusion/stream levels on demand.
• Profiler – GPU traces identify render bottlenecks.

Unreal’s actor/component model is designed for optimal memory layouts during gameplay. And its renderer is highly optimized for mobile and console platforms.