When to Use ECS Instead of MonoBehaviour: A Narrative

From MonoBehaviour Mess to ECS Bliss: My Game Dev Awakening

I remember staring blankly at my profiler. Hundreds of zombie enemies, a sprawling city, and a framerate that choked on its own ambition. My beautiful zombie horde game was, well, dead on arrival. MonoBehaviour, the cornerstone of Unity development, had become my performance prison.

At first, I blamed the art. Maybe those high-poly zombie models were the culprit? I optimized textures, decimated meshes, but the needle barely moved. Then came the scripting deep dive. Countless GetComponent calls littered my code, update loops were bloated, and object interactions created a cascade of overhead. I was trapped in MonoBehaviour hell, and I needed a way out.

That’s when I stumbled upon ECS: the Entity Component System. It sounded daunting. Data-oriented design? Archetypes? Entities without behaviour? It was a paradigm shift, a complete rewrite of everything I knew about game development. Panic set in. A full rewrite felt impossible.

Instead, I decided to experiment. I started small. The simplest part of my game was the movement of debris - little chunks of destroyed vehicles, generic rubble that reacted to explosions. I converted just the debris movement to ECS.

The initial results were… underwhelming. The code was more complex, harder to read, and the performance gain was negligible. Discouragement loomed, but I kept digging. The problem wasn’t ECS itself, but how I was using it. I was still thinking in MonoBehaviour terms, creating individual components for every little thing instead of grouping related data together.

My “Aha!” moment came when I realized ECS was about data transformation, not object manipulation. I refactored the debris system. I combined position, rotation, and velocity into a single Movement component. I processed all debris entities in a single, efficient system. Suddenly, the profiler sang. The performance improvement was significant, almost magical. The debris, once a minor performance drain, now barely registered.

This small victory gave me the confidence to tackle a bigger challenge: the zombies. I didn’t jump in headfirst. Instead, I focused on the movement of the zombies. Just like the debris, I created a dedicated ECS system for handling their velocity and position updates. I still used MonoBehaviours for things like AI and animation, but the core movement logic was now handled by ECS.

The result? A dramatic reduction in CPU usage. The zombies, once a major bottleneck, now moved smoothly and efficiently. I could finally add more zombies to the horde without tanking the framerate.

It wasn’t a complete overnight transformation. I still had to profile, optimize, and learn the nuances of ECS. Some systems, like the complex AI logic, remained in MonoBehaviour because the overhead of converting them outweighed the potential benefits. ECS isn’t a silver bullet; it’s a tool, and like any tool, it needs to be used judiciously.

Here’s what I learned through this painful, but ultimately rewarding, process:

• Profile first, refactor later: Don’t blindly convert everything to ECS. Identify the biggest performance bottlenecks using the Unity profiler, and target those areas first.
• Start small, iterate often: Don’t attempt a complete rewrite. Focus on isolated systems and gradually migrate them to ECS.
• Think data-oriented: ECS is about processing data efficiently. Group related data into components and process them in parallel systems. Avoid creating unnecessary components.
• Embrace the hybrid approach: Don’t be afraid to mix MonoBehaviour and ECS. Some systems are better suited for one approach than the other.
• Track your progress: Documenting my journey was crucial. I used a game dev journal to record my experiments, successes, failures, and the performance gains I achieved with each adjustment. This helped me learn from my mistakes and make informed decisions about future refactoring efforts.

Now, I’m not suggesting everyone abandon MonoBehaviour entirely. It’s a powerful tool, especially for smaller, less performance-critical projects. But when you’re dealing with large numbers of entities or data-oriented logic, ECS can be a game-changer.

And speaking of tracking progress, if you’re serious about improving your game development skills, I highly recommend keeping a detailed journal. It’s not just about recording what you did each day; it’s about analyzing your decisions, learning from your mistakes, and tracking your performance improvements. A solid game development log helps you stay consistent with your devlog, keep track of your progress, and organize your creative process. If you are looking for a better system to do this, you can start your game dev journal here to document your learnings and make informed decisions moving forward. It’s a game-changer!