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Building Simulations, Part 1
by Borut Pfeifer on 08/13/13 04:50:00 pm   Expert Blogs   Featured Blogs

The following blog post, unless otherwise noted, was written by a member of Gamasutraís community.
The thoughts and opinions expressed are those of the writer and not Gamasutra or its parent company.


In all the post-mortems and production methodologies for game development, none really address the difficult problems of building a simulation-heavy game in a non-insane way.

With my experience working on Scarface, LMNO, game AI in general, and a side project I’m starting that delves heavily into crowd simulation, I wanted to formalize my thoughts on production processes for simulation driven games.

I mean to answer the question of how best to tackle creative and production challenges, in a way that will most quickly get you to a point where the game is compelling to play (and therefore also viable to pitch and market before being complete).

 X is for Overused

The most predominantly official production process for games is the Cerny method. It’s called all manner of things in practice, first playable, vertical slice, but it primarily invoved building 2-3 minutes of polished experience including gameplay, art, sound, etc. before the rest of bulk of the game’s content. That reduces the amount of content that has to be completely remade as other assumptions change. While you never completely escape that, this method certainly helps.

At EA it was broken down even further – after an initial concept phase, there was the X-Slice (same as above), followed by the X-Level. The X-Level represented 10-15 minutes of gameplay, but additionally required all tools and other pipelines to be fully working. This extra time to focus on tools helped to make sure that content could be added to the game as quickly and as easily as possible during full production.

Content Is Killer

You’ll note the repeated use of the word content or synonyms for it in the above description. This methodology best (perhaps only) applies to games built on a small set of very repeatable mechanics and systems – the fabled “30 seconds of fun”. The game then staggers levels, characters, other art, with minor changes in systems for pacing across the entirety of the game.

After the initial vertical slice is complete, you generally feel confident in judging the gameplay, understanding what needs to be added, and how long it will take to create assets for the game. You are completely unable to do this if your game is a simulation, though.

You Know It When You See It

So what defines a game as simulation-driven? It’s not always a strict avoidance of a level/content based progression in the game. The Thief series is level-based, but its gameplay comes from a series of connected systems. The space in which the gameplay takes place is one of those systems.

Some examples are easy to spot – The Sims’ gameplay is driven purely through the interactions of the various systems, the Sims, their goals, the objects they can use, and building houses full of those objects for your Sims to interact with.

Skulls of the Shogun, as a strategy game, features quite a few systems. But it’s not simulation driven, although many strategy games may sit on that fence. The distinction is that gameplay in a simulation stems from second or higher order interactions between systems. In Skulls, the various systems interact to give you lots of strategic possibilities, but we tried to make the consequences as clear as possible to make the strategy more accessible. (The higher order consequences are more for advanced players to explore and not part of the base gameplay).

Second or higher consequences occur when a player’s action in a system has an impact in another system. That may impact another system, and so on. The gameplay stems from dealing with those the second order consequences – either reacting to (in the case of a stealth game like Thief), managing (in the Sims), or a mix of both (in an open city game like GTA).

Lots of game feature simulations – the physics behind a racing game or Angry Birds, but those higher order consequences have to be a key part of the gameplay experience. That’s when the simulation & all its systems not just affect, but completely define the player’s experience with the game.

A Field Full of Broken Dreams

Building a simulation driven game, you can’t judge the player’s experience with 2-3 minutes of gameplay. Those 2-3 minutes might only involve 20% of the game’s systems. And while adding art and sound assets is still time consuming, the experience is driven by complex, layered, system interactions.

You could start adding shipping content to those systems, but without the remaining systems roughed out, the systems you do have will surely change. Those assets need to support the system feedback the player needs, so if the combination of systems are not proven, pushing a high fidelity art asset into the game is useless. As soon as one of those systems, even if it’s a different one, changes, that asset might not even be needed.

In my 13+ years making games professionally, I’ve seen or heard of the Cerny method applied to simulation driven games many, many times. In no case has it ever gone even passably alright, causing heavy delays and more often than not, tanking the project completely.


In that sense any work done before the simulation is refined is wasted effort, just like building extra levels was wasted effort before the Cerny method. But what you need in this case is maximum connectivity between systems.

What that means is that each system may not have all of its mechanics implemented (ideally has as few as possible), as long as all of the rules that connect to other systems are implemented. That includes any lower-level mechanics that are necesaary to build those connections.

Coming Soon…

The rest of the series will delve into specific milestones and how they are necessary for development to reasonably progress. In my next part, I’ll look at what’s uniquely required out of the concept phase for a simulation based game.

This was cross-posted from my blog.

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Michael Joseph
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I look forward to the rest of your series on this subject. But for completeness sake, can you describe as you see it, what differentiates a "simulation driven" or "simulation-heavy" game from another type of game that might be confused as one?

I think you touched on it when you talked about content driven games -- "This methodology best (perhaps only) applies to games built on a small set of very repeatable mechanics and systems." and "Building a simulation driven game, you canít judge the playerís experience with 2-3 minutes of gameplay."

Most of us can clearly recognize a hardcore flight sim, space sim, _____ tycoon sim, or open ended Mount & Blade type game as a simulation driven game, but what else might you be referring to?

Borut Pfeifer
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That's a great point Michael - I was sort of operating under a "you know it when you see it" approach, but there's definitely other examples, like the Thief series, or even most open world games (which we don't often think of as sim games but whose gameplay & pacing is really reliant on their systems). I'll try to clarify in the next post.

Bart Stewart
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"[C]an you describe as you see it, what differentiates a "simulation driven" or "simulation-heavy" game from another type of game that might be confused as one?"

I'd like to take a swing at that.

How about, "The greater the number of distinct systems that generate behavior states without requiring direct player input, the more the whole system is a simulation."

By that definition, a game that largely "does its own thing" without the player poking it, the more simulationist that game becomes. So a fighting game, for example, is very non-simulationist, and probably would be well-represented by a vertical slice. But a game implemented as a world with day/night cycles, weather, seasons, predator-prey relationships, and emergent crowd behaviors would be highly simulationist. (Relative to most games, anyway.)

I'm inclined to think Borut is absolutely right; trying to represent that latter kind of gameplay -- and it is gameplay, of a certain kind -- with just a slice would almost certainly fail to show what playing that game would really feel like.

I'm looking forward to the next installments in this series!

Brian Bartram
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As somebody who worked on the recent SimCity and on the Dead Space series I'd have to agree totally. You just can't predict what is going to happen in a simulation game the same way you can with a level based game.

Mike Lopez
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Nice post, Borut.

I would argue that it is not a problem inherently with the use of vertical slices in these types of games. In my view the problem instead lies more in the enforcement on what constitutes a true vertical slice of gameplay, rather than what limited systems/mechanics can be completed in one or two milestones that the team and/or publisher has devoted to "vertical slice" and prior to moving into full Production. I would also agree 2-3 minutes of gameplay doesn't provide a true full experience.

Cerny, Will Wright, Miyamoto and perhaps a few other well known and well marketed designers have the luxury of ample time and resources to keep tinkering and proving out all pieces of gameplay on a large team before full production has started, which is why I always thought strict adherence to the Cerny Method impractical. However, most industry people who work for medium, large and giant developers or publishers sadly do not have that luxury and I submit that vertical slices can still be useful even if they are not complete and do not accurately reflect the complete system interactions. Just so long as no one expects that to be 100% representative of the final game.

The real value in vertical slice/relaxed Cerny Method approach in my view is from an Agile perspective where the team is forced to build features, systems and mechanics that are the most important first and hopefully to demonstrate the fun of gameplay. Compare that scenario to a team that uses Waterfall development and few of those features and mechanics come on line until deep into development (sound familiar?).

Borut Pfeifer
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Yeah, I mean to explore that more later on - the concept of a key milestone like the vertical slice is still super important, but the term vertical is the problem. It's more like a horizontal slice, where you have all the systems in a super rough place, but you can still see the fun/interestingness because the experience is more about how they connect.

It's hard too, because I think teams instinctively want to go super deep and polished on something as crafts people. On Scarface I was remembering that we actually had all this tech w/vehicle damage, and being able to shoot out of them while driving, all this stuff, before I finally plugged in the sandbox where you drive, shoot, avoid pedestrians & traffic, fight randomly spawned gangsters, etc. :) And then people finally responding to that like "Oh yeah it's not about any individual piece". I mean, the open city game wasn't a genre at the time, there was just GTA, so that definitely made it harder to convey that.

Mike Lopez
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Yes. I would agree the term vertical is not a great fit because there are missing pieces and the systems/mechanics are still rough. Only Cerny, Wright and Miyamoto have the luxury of ongoing R&D until everything is polished and tight.

But I still think the vertical slice ideal is an important target to work towards. From an Agile perspective I also think that everything bit of gameplay in that milestone should be reworked, tightened and polished multiple times before tertiary systems, mechanics or features are even started to be developed and maybe you even scope some of these extraneous things out once you realize they are not needed.

Mike Lopez
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Racing games are built on simulations and one can deliver a vertical slice without traffic, opponents, weather, decals/body mods, performance upgrades and many other systems on line. We delivered those types of vertical slices with Road Rash on multiple versions and I felt that was helpful to development risk.

On Scarface what we called a Vert Slice was really more of a polished art deliverable without all the tech, systems and mechanics that should have been proven out before we entered Production.

Borut Pfeifer
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Ergh gama ate my first try to respond - I would disagree though that a racing game is what I mean by simulation driven. I mean, on the one hand, yes, physics features prominently. But it's only got 2-3 really super deep systems, as opposed to a larger number of systems that connect with higher order consquences. So the gameplay is all about exploring those few systems, and not playing with multiple systems to figure out how they connect.

Mike Lopez
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Thanks for the clarification. I buy that distinction.

Good discussion.