Proceduralism: Part Six (Architecture)

[You'll probably want to read the original article series that inspired this follow up, then start with parts one, two, three, four and five of this series.]

Edge Magazine recently featured an article, Building Worlds with a Single Click, which highlighted and praised two exciting new projects by independent developers: Project Frontier by Shamus Young and Procedural World by Miguel Cepero, both of which feature beautiful procedurally generated worlds.

The thing is, we've got very good at building procedural worlds - so good that virtually every example uses the same small underlying set of well understood systems: noise, L-system based architecture, Whittaker diagrams and so on that even a single programmer working in their spare time can implement. Just to pick a few featured in the World Building page on the PCG wiki: Making Worlds, Procedural Planets, Dungeon League, Polygon Map Generation. And of course, there's Infinity: the Quest for Earth, L.o.V.E. and Spore; all of which feature incredibly detailed environments created by incredibly talented and smart programmers.

And all these amazing worlds? Almost everyone is focused on building these curate's eggs - which, if they eventually end up being released as a game, become a disappointing, empty and lifeless one.

[Edit: Miguel Cepero has responded to this post, and quite rightly points out that the above statement is not a nice thing to say, specifically when his and Shamus Young's project should not be judged on this basis as they have not been released. I would like to apologise for making this generalisation, which the article in Edge magazine points out is the big challenge that all these projects face.]

Does almost all procedural generation amount to, as John Carmack puts it, is "a really crappy form of data compression"?

My procedural spider senses tingle as soon as I see a procedural generation system that uses one of the following two approaches:

1. Mazes (and by extension BSP-trees)
2. Height maps

because I've yet to play a game where I've exclaimed 'Wow, what a great height map' (except Populous, but we'll get to that) and the pleasure of solving a maze isn't the same as the pain of having to play through one.

I've also seen a rise in recent suggestions and several implementations of Metroid-style procedural generation featuring gated lock-and-key puzzles to partition a map, on the assumption that being forced to traverse through a non-linear space looking for a key is some how interesting. This is putting the cart before the horse: Metroid (and Zelda) use this technique to force the player to explore an already interesting (and hand-designed) location, not because looking for a key is itself challenging. The lock-and-key puzzle is merely a dressed up fed ex quest where you're not told the location of the package you have to deliver (or worse, you stumble across the package without knowing its destination address).

When we talk about architecture in game play, we don't think of buildings and naves and antechambers: we refer to choke points, and cover, and objectives. The topology of the space is much more important than its aesthetic or fidelity. The most successful (and perhaps only successful) procedurally generated game spaces so far are all based on Rogue, with its simple room and corridor design.

With a room and corridor design we get four important features:

1. Corridors - which act as natural choke points at each end, and cover if you are in them
2. Convex shapes - spaces where you can see everything in the space from everywhere else
3. Concave shapes - spaces where some space is hidden from another (more cover)
4. Loops - which allow you a safe haven by traversing the loop to recover when chased by enemies of the same speed or slower

Elite, the other arguably successful procedurally generated game space, remains interesting because it is a procedural objective generator. Here you are searching for trade routes between high tech industrial and low tech agricultural worlds: the topology is interesting only because every edge is a potential goal.

Populous, Dwarf Fortress, Minecraft and Terraria all cheat procedural generation in two important ways: they allow you to modify the topology of the space and they encourage you to make interesting content in that space to which you become attached. An uninteresting dead end can be transformed into a useful corridor, or lit by a torch to mark that you've 'already been here' or mined for valuable ore. The procedural generation systems they use may make beautiful places, but it is the player's job to change them into interesting spaces.

It helps in the case of Minecraft and Terraria that much of the procedurally generated spaces mimic Rogue's room and corridor layout. Strategy games generally generate a mix of the Rogue-type (open areas, choke points defined by inaccessible terrain) and generation of objectives through resource scattering (call this Civilisation-type PCG).

Even with a room-and-corridor design, the architecture, or more correctly topology of a space is insufficient to lead to great procedurally generated games. As I discovered when working on Unangband dungeon generation, it is the contents of these generated spaces that is the most important part of procedural generation. And that is why it is so frustrating to see developer after developer get trapped in architecture, distracted by beautiful world building, and not concentrating from the start on the creating content.

And I'll be discussing content in part seven.