Wednesday, May 27, 2009

Multilinear Level Design For Left 4 Dead

Wednesday, May 27, 2009

Two pages from my sketchbook, as I puzzle out nonlinear level layout possibilities for L4D.

Left 4 Dead is a well polished, mostly traditional FPS experience with a notable innovation: the Director.
Valve designers found that no matter how cleverly zombies were placed, players would quickly begin to anticipate them on repeat playthroughs. So they developed an ingenious system to handle the zombies.

The AI "Director" controls most of the zombie mobs placement and modulate their strength in lieu of traditional designer placement. This makes for wildly variable experiences in terms of enemy encounters, density, and where the Survivors make their defensive stands/when they decide to run.

But on the heels of the L4D SDK's release, my thoughts return to how this governing principle might be more completely extended through the experience--namely the level design.

My own experience of the excellent co-operative L4D experience was that I enjoyed it, but felt not much prompting to replay it because I had experienced the whole "ride".
Despite being a superior specimen thereof, it's still of the linear "funhouse" style FPS experience. I creep around the next corner of an expertly crafted environment, but my friends and I have no say as to where we're headed, which seems contrary to the spirit of a "surviving a zombie apocalypse" game.

Just as the Director unmoors zombie placement from direct designer control, what if the level layout were (to a smaller degree) unpredictable? What if alongside semi-random obstacles and dead-ends, the players had to fight but also actively navigate to freedom?

Arguably this is counter or more complex than Valve might deem desireable or saleable, especially for a game so well designed for perfect casual 30-45 minute play sessions. But for players who have invested enough time in the game and want a more challenging but also more varied experience, I think the idea has merit. Certainly worth further inquiry.

The initial plan is for the player start to be in the dead center of the map, with roughly four main paths radiating outward, like a pinwheel. In addition to these four main trunk lines, there would be interconnecting spokes. This gives players four possible paths with out-bound linear paths, but also lateral movement by way of the spokes.

The "pinwheel" design sketch. The paths are in a roughly square configuration to minimize lateral travel time between main trunk lines. In a finished layout, the actual player-paths would be more s-curved and kinked.

Instead of simply choosing one of four paths--in which multiple playthroughs would very likely expose one to be the easiest path and become preferential to players--there is a degree of chaos introduced by semi-random blockages or dead ends that would appear at various points along these paths and spokes.
This plan is far from a "sandbox" approach, but would ideally allow for complexity by way of multilinearity.

Further updates as I refine and implement a test case with the L4D SDK.

UPDATE: Multilinear layouts are not supported by Left 4 Dead.

Screenshot from test level. It shows that despite the test level having two safe rooms, the escape_route--how the Director and AI reckons player progress through the level--can only route to one of them, not both.

The bright spot here--other than providing a nice way for me to familiarize with L4D's AI/navigational architecture--is that I successfully predicted a design issue with a multilinear path.
Above I wrote that the trouble with multiple routes is that players would likely adapt to one preferential route quickly, without something like semi-randomizing dead-ends or blockages.

After writing the above update I downloaded the SDK and starting working with it. Then I remembered that I hadn't played the L4D commentary mode, and so I played that.
In it, one of the developers (Mike Booth maybe?) mentions trying an early non-linear city block level, and that the trouble was in fact that experienced players quickly found a preferred route (and that bickering about which route to take taxed teamwork).

Now, I don't think this would be as much of a problem if different routes actually provided vastly different endpoints--such as heading north means the suburbs, west means the slums, east meant the industrial outskirts and south meant the forest--but at this stage that's pure conjecture.
L4D is a particular sort of game and a very good one for the design elements chosen. I'll have to wait for another opportunity to experiment with the kind of level structure as outlined above; in the meantime I'm still quite piqued at building a L4D map/campaign.


Anonymous said...

Why are you just working at shitty little indie places?

gauss said...

I'm not working anywhere at the moment, actually. And I'm fully open to the possibility of life in the big leagues (and a variety of other sports-related metaphors) for getting my next job.

Johnnyburn said...

Interesting that they had to design the mechanics to minimize bitching. I suppose with a co-op game, that is an important design element.

Anonymous said...

So you wouldn't mind working under a big, bad publishing contract with EA or something? You struck me as the kind of faceless internet entity that would rather work in a small company.

gauss said...

Preferential option to small teams, but then I've never been inside the big bad machine when the machine is well oiled, so to speak. In my limited experience a good project (and working for/with people you like) can go a long way, beyond other considerations.

Anonymous said...

Either way you better have an update when you do get on a team; I really enjoy your ideas, the presentation of them, as well as your drawings. I would detest working in the video game industry, but you seem to fit into the system pretty well.

gauss said...

Thanks. Much obliged for your both your interest and your comments. In fairly rapid order I'll be revamping the portfolio (and the art blog linked below), expressly to find employment again. So when I find out I have a new job, the news will certainly show up here.

Anonymous said...

I think this sounds like a great idea. Though the bickering aspect is an interesting point.

Funnily enough I think nearly all Zombie movies have a bickering scene in them, but I do find this obsurd. Would a group of people fight each other when surrounded by sleeping lions, no.

Perhaps one way around this would be to have scripted events which either block or reveal a new path based on the players actions. Such as killing a tank before it blocks their path and they have to find a new route.

Anonymous said...

...Oh or keeping zombies off a bulldozer long enough for it to clear a path.

gauss said...

Funny enough, I wrote this update just about the time when Valve revealed that L4D2 would feature semi-randomized maze-like level portions, which really produces a kind of best-of-both worlds effect. They can still smartly pace the level as a linear experience (pacing is pretty central to how the Director works, it's a brilliant bit of design), but also have sequences that vary wildly from playthrough to playthrough. Not that I wouldn't still like a chance to develop this "pinwheel" design... maybe some day there'll be a better candidate to try it out with.

And yeah it is funny to think about removing bickering when it's true, you always have that scene in zombie movies :) It's part of the experience!

Ian Meharg said...

Ah, I wonder if L4D2 would work better for this map I've been working on since late summer (I finished the map, it's the MESH that's the problem).
There are two distinct paths to the final saferoom, but one is conditional: you can only access it if zombies break through a wall. For a while now I couldn't understand why the ESCAPE_ROUTE couldn't be created, but I was wrong in assuming that: it was being created, but could only be seen when the breakwall was open. In other words, the breakwall route is shorter and thus more appealing to the ESCAPE_ROUTE. Thanks for reminding me of this!

gauss said...

You're welcome--good luck with the map. Remember to iterate your nav mesh for anything like breakable walls, elevators and the like, for all the different states and then regenerate.

And I'm glad you brought that up, this was written some time ago obviously and there are some exciting new options with L4D2.

Dhatz said...

your theory would work for single player, but how would the coopers decide which way to go?. it would only break the neccessary coherence.

Sadin said...


I think that the different routes and choices are part of the appeal, it'd promote teamwork rather than lead to a break down in it.

The idea could be really groundbreaking if implemented properly and carefully, not just thrown into some random game.

I've always been very interested in making games more dynamic, it's very nice to read your ideas.

gauss said...

Good comments, people.

Dhatz: I think it's a question of the kind of game they want to build and to market. L4D does deliver on a pretty thrilling experience, but for example L4D2 I haven't picked back up once since I finished through the campaigns (though I played Hard Rain and a few others multiple times). Once I've laid the needle in the groove it just feels like I'm going to hear the same record every time, but maybe with just different parts faded in and out, you know? That's less of a game to me.

It's an inevitable comparison and I'm going to make it here, too: L4D and Killing Floor. The latter lacks all the sort of dramatic sweep of the connected levels--they might think of releasing a campaign level set, in fact--but it makes up for that by being a lot more interestingly free form. Where L4D cripples many player actions such that they are forced to work together, Killing Floor makes no such overt calls... simply making it highly, highly unlikely you will survive if you don't work together. The former creates a feeling of co-operative play which may be genuine, may be entirely counterfeit, whereas all my successful Killing Floor rounds feel like more genuine victories.

Not to say that they're not both worth playing, but in the (hopefully ebbing) generation of zombie games, they make for an instructive comparison.

Sadin: thank you very much. Fostering interesting discussion of ideas was much of what I had hoped to do with this site.

Anonymous said...

I've thought about this before myself, and something that always came up was the style of 'mysterious dungeon' games (Chocobos mysterious dungeon, azure dreams, etc etc) These games use randomly generated maps that follow a core set of rules, ensuring there is always an unobstructed path (or 2) between one 'floor' and the next. It does these on a simple 2 dimensional grid (with some depth added for statistics sake mostly) but couldnt there be some way to design a cavern, or a city system of some sort that uses the same principles (in 2 or 3 demensions of map acess) to design obsticals? I'm not claiming it would be easy but certainly its not impossible.

Anonymous said...

heel yeah!!

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