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Designing a Game Engine is Hard

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There is something about designing a game engine that is both alluring and terrifying. My ten years of programming experience feels like nothing when I am faced with that challenge. Many times I've wondered why I feel so compelled to build one of these systems, considering that it is effectively reinventing the wheel the hundredth time. Why not just use an existing engine out there? I have seriously considered this, but in the end, I find myself more intrigued with game engine technology than games themselves. That is where my passion lies.

I have made a few attempts at building a game engine, and those have all failed for various reasons--the paramount reason being poor design decisions due to inexperience. My most recent attempt was a 2D game engine intended to power casual games similar to World of Goo. Unfortunately, components were so tightly coupled in all the wrong ways that functionality quick devolved into glorified hacks. For example, my entity system was confusing, inflexible, and difficult to use, as were the physics and scene managers. It came to a point where the design was salvageable--so I abandoned the project.

Like Thomas Edison, I successfully found a way not to build a game engine. It was hard for me to accept that my final result was essentially worthless, but the point was to learn. With that experience behind me, I now plan to build a simple 3D engine from the ground up. Hopefully this time I will avoid some of the pitfalls that I encountered in my first attempt.

One thing that I plan to do differently this time is put a lot more effort into the design stage of development. I ended up rewriting several parts of my engine and wasting valuable time because I realized my requirements weren't adequate. I decided on a name for this new engine: Tiny. The reasoning behind this name is fairly obvious. I want to minimize the amount of bloat, yet still provide a strong toolset that allows developers to have more control in the game building process. This engine will be code-based, so I don't expect to build virtually any point-and-click tools for development.

One particular aspect of the design phase that I want to stress is the use of interfaces. In my previous engine, I added interfaces after parts of the engine were already built--which basically defeats the purpose. I think building interfaces can be a huge aid in the design process, because it forces developers to think about how components interact with each other. With a good set of interfaces, the intricate relationships between components are already fleshed out, lessening the chance of one of those "Aha" moments of forgetting to include some vital piece of data or functionality. This may seem obvious to some people, but the learning process has been slow for me.

I am in the process of building a list of requirements, designing a high-level schematic for the engine, and gathering the list of third-party APIs that I plan to use. Here are the requirements so far:

  • An engine backbone class that facilitates initialization of core subsystems like Input, Sound, Physics, Graphics, and Networking, as well as game state, resource, and window management.
  • An event system which oversees message passing between engine subsystems.
  • [color=#000000][font=Arial]

    DirectX 11 based renderer which natively supports HDR lighting, SSAO, motion blur, and depth of field.

  • [color=#000000][font=Arial]

    Template based resource managers for various resources such as textures, meshes, materials, shaders, and scripts.

  • [color=#000000][font=Arial]

    A world management system that supports loading/unloading maps, adding/removing entities, and updating and rendering the world.

  • [color=#000000][font=Arial]

    A text based map format that supports a set of static world meshes and entities of various types.

  • [color=#000000][font=Arial]

    A component-based entity which localizes all parts of the entity into one object--such as rendering, physics, AI, input controller, etc.

    [/font][/color] Components will communicate through the event system.
  • A robust error logging system.

    The scariest part for me is designing the entity system and world manager. It is such a balancing act to avoid building yourself into a corner with a completely decoupled system, or a cluttered fully-coupled system. I hope that I can do better than last time.
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