the artistry and psychology of gaming


The Architecture of Half-Life 2

The Architecture of Half-Life 2

If you were to ask a group of typical gamers what the most important parts of video game composition are, you’d receive a variety of different answers. Chief among them would likely be the gameplay and controls, and they should be, as they are the backbone of any video game and the element that separates games from other media. Story would probably be mentioned several times, and a great narrative can add a lot to a game, but Mario’s managed without it just fine for over two-and-a-half decades now. Some might cite the audiovisual presentation as paramount, and while it is important (especially art design), it is far from the most critical element of a video game.

Something you probably won’t hear mentioned too often is level design. This is disappointing, since level design is one of the most important aspects of video game composition, second only to gameplay/controls. Superior level design can elevate an average game to greatness, while inferior level design can ruin an otherwise solid game. This is why I have chosen to begin this feature and celebrate the hitherto unsung architects of the virtual world.

(While I will avoid mentioning specific plot details, I will often describe areas of a game in detail, and those can be spoilers in and of themselves. You have been warned.)

This inaugural installment of The Architecture of Gaming will focus on a game that has quite possibly the greatest level design of any video game ever: Half-Life 2. Before Half-Life 2’s release, the hype train almost sped off the tracks, thanks partially to the protracted five-year, $40 million dollar development cycle, and partially to the acclaim garnered by its revolutionary predecessor. When the launch date came, this sequel not only met the incredibly high expectations, it far surpassed them. Sublime controls, graphics that still hold up seven years later, perfect sound and an amazing physics engine combine to create one of the greatest and most essential games of all time. In other words, Half-Life 2 was so far ahead of its time, you may as well call it McFly.

“Whoa, this is heavy.”

Of course, we’re here to discuss level design. Level design is both an artistic and technical process that involves many distinct facets. Half-Life 2 does so many things well that it’s a perfect way to introduce many of these concepts. Not all of these are necessary for a game to have excellent level design, but a great game will generally succeed at most of them.

While this article focuses on Half-Life 2, I will also mention things that were done well by the original Half-Life, as well as the two episodic games that continue HL2’s story.


Topography, in other words, is the layout of the terrain. In a game with linear levels – like most platformers and many first-person or third-person shooters – there must be an interesting way to get from the beginning of the level to the end. Even if there is only one path through the level, that doesn’t mean it has to be a long, perfectly straight hallway. Ideally, the terrain should be an obstacle in and of itself. While this is almost the entire point of a platform game, varied and hazardous terrain can add a lot to other game genres as well. A firefight in large empty room could be made much more tense and exciting if there are open vats of radioactive acid (OSHA be damned!) or if the shooting takes place on narrow ledges along a sheer cliff face. (Note that these are both situations which occurred in the original Half-Life.) Even if you’re just traipsing from one shootout to the next, some varied challenging terrain can keep your mind sharp. Trotting from one identical hallway to the next essentially means that all you’re doing is watching a looping animation of your character running. However, if you have to find a rickety catwalk or pipe and carefully navigate along it to cross a pit, that ensures that you are continuously playing a game.

In games with more non-linear level design – like Metroidvanias, sandbox games and many action-adventure games – navigation should strike a balance between challenge and convenience. The first time through any given area, progressing should be difficult, and there should be a heavy focus on exploration. However, repeat visits shouldn’t become a chore; warp points, shortcuts and “fast travel” can help. Even in open-world-type games, there are usually portions of the game that are still fairly linear (i.e. dungeons).

Half-Life 2 fits squarely into the former category. From the very beginning, Gordon Freeman is led down a rigidly linear path with very little room for deviation – the G-Man makes sure of that. But just because the game is on rails, don’t think of it as a slow, boring train ride; think of it as a roller coaster with twists and turns and loops. And headcrab zombies.

While Half-Life 2 is classified as a first-person shooter, it also draws a lot of influence from platform games. Jumping tends to be more important than in other FPS games, and there are a number of segments that wouldn’t be terribly out of place in a Mario title. Normally, putting platforming sections in a first-person game is one of the mortal sins of game design: jumping across gaps can be a real pain in the ass when you can’t see your feet. However, some intelligent design choices on the part of Valve keep the platforming from being frustrating. Firstly, the developers don’t expect the same level of precision from the player that a regular platform game does. Gaps are never very large; each platform has more than enough room for you to land on it; and if you have to walk across something very narrow, it’s usually against a wall so you can only fall off of one side. Secondly, many of the platforming segments (including almost all of the most difficult ones) do not outright kill you if you fall off a platform. There are a handful of sections with deadly drops, but for the most part, you are just jumping over harmful substances, and you can simply climb back onto the nearest patch of safe ground if you fall in. Lastly, there is no significant knockback from enemy attacks, so a well-placed bullet or leaping headcrab will never push you off of an edge while you’re lining up a jump. In short, Half-Life 2 doesn’t expect you to do upside-down wall jumps over spike-filled pits; the platforming is just intensive enough to add an extra layer of challenge to some firefights, and make navigation more interesting.

The platforming segments over harmful material are also notable in that they utilize the game’s celebrated Gravity Gun. If you’re trying to reach the other side of a pool of toxic sludge, you can use the Gravity Gun to grab large physics objects and make your own stepping stones. Hazardous materials you can cross this way include electrified water, radioactive waste, and sand that summons monsters when you step on it. Surprisingly, none of the “Floor is Lava” sections take place over actual lava, but considering that this is a game about a physicist, the dev team probably knew better than to do that.

“Convection? What’s that? Can I punch it out of my way?”

Another thing you may notice about Half-Life 2 (as well as most other Valve games) is the incredible economy of space in the level design. In other words, they cram an awful lot of level into a tiny area. Many video games feature large rooms that resemble space-filling paths or unicursal labyrinths, but Valve takes the concept further than most. In fact, in Half-Life 2, it’s not uncommon to look through a chain-link fence and see an area that you were running through ten minutes ago.

From left to right: space-filling curve, unicursal labyrinth, Pan’s Labyrinth

If that sounds like Valve made the path twist and turn so that it would take half an hour to travel 100 meters, that’s because that is more or less what they did. And it would be really annoying if they did this with an empty path snaking through a bunch of standard walls. Thankfully, Valve is much more creative than that. (Granted, there is a bland serpentine path through chain link fences at the very beginning of the game, but what else would you expect in Airstrip One City 17?) The winding path through the game was designed with all three dimensions in mind, and the barriers separating different parts of the path include fences, solid walls (in some cases you may not even know how close you are to another part of the level), gravity barriers (steep slopes or deep chasms), or the ceiling/floor. For an example of that last one, Half-Life 2: Episode One includes an area where you must run through a series of open intermodal shipping containers before looping around and running across the tops of the containers. It’s also far from empty; each twist or turn presents new challenges, such as enemies, platforming, or puzzles.

To see all of this in action, play through Ravenholm, paying attention to landmarks and trying to keep your sense of direction. You’ll find that that particular level has you running down streets and alleys between buildings, navigating the interiors of the same buildings, and also jumping across the rooftops of – you guessed it – those very same buildings. You may also notice that whenever an outside area has two elevations (like the streets and the rooftops above those streets), the higher altitude will almost always be reached second. This is an easy way to make sure the player doesn’t jump down to take a shortcut, without resorting to cheap instant death fall barriers, à la Halo. (Ravenholm also gets bonus points in my book for the bit where you use one of the “falling car” traps as a makeshift elevator.) Overall, Ravenholm manages to compress at least half an hour of gameplay (if you know what you’re doing) into a very tiny area. Remember that stretch of train tracks immediately after Ravenholm that takes a few minutes to clear at most? That runs along the entire length of Ravenholm, and then some.

Click the image to see the full-sized picture.

This economy of space can have some benefits for the player as well. It allows you to use the Gravity Gun to launch helpful items (such as saw blades) to areas you know you’ll visit later, to ensure that you’ll have a proper zombie-chopping tool when you get there. This strategy is also invaluable if you wish to help a certain garden gnome achieve his dream of becoming an astronaut.

Finally, I’d like to mention one last thing about the level layout in Half-Life 2. There are very few sections that require extensive swimming, and you’re never in the water for more than a few seconds. Since water levels almost always suck, this is a very good thing.

Mission Objectives

One aspect of level design that is closely intertwined with story is the variety of objectives you have to fulfill over the course of a game. Basically, the story determines why you have to do what you’re doing, and the level design determines how you will do it. In today’s world of lowest-common-denominator entertainment and “follow the leader” mentality, it’s nice to see a game with a wide variety of mission objectives that extend beyond “murder everyone.” Granted, if a single objective is recycled through an entire game, that doesn’t necessarily mean that the game sucks. 95% of all platformers are based entirely on either “get to the end” or “collect all of the things,” and they still manage to have great level design. The positive effect of interesting mission objectives is a lot greater than the negative effect of overused goals, because the latter can be overcome with excellent gameplay.

The Half-Life games are interesting in that they never explicitly encourage you to go on a killing spree. Sure, you’re going to be placing a lot of bullets into a lot of skulls, but just about all of it can be chalked up to self-defense. I’m not claiming that Half-Life is on the same level as Metal Gear Solid or Deus Ex in terms of being pacifist-friendly. However, your primary objective is almost always either “stay alive” or “find the next plot-important person/item,” and that puts Half-Life one step ahead of most other first-person shooters.

Hidden Stuff

It seems like no one can make a video game nowadays without scattering a bunch of hidden collectible trinkets throughout the environment. They are always optional, rarely plot-relevant, and usually offer no greater reward than an Achievement/Trophy for hoarding all of them. I personally call these things Assassin Flags. I probably won’t mention these very often while discussing level design, since most developers are content to simply hide them around a corner or slightly off the beaten path. However, developers will occasionally get clever with their Assassin Flags, concealing them in creative and interesting ways. Once again, this is something that doesn’t necessarily hurt a game if it isn’t done well, but if it’s worth mentioning, I’ll point it out.

The hidden collectibles in Half-Life 2 take the form of ammunition caches marked by a nearby lambda symbol. They don’t exactly qualify as Assassin Flags because they are immediately useful, but finding all 45 of them does award you with an Achievement (ever since Half-Life 2 was included in The Orange Box). Some of them are actually concealed rather cleverly, requiring you to do a bit more exploring than you’d expect to do in a Half-Life game in order to find them all. Episode Two featured two separate sets of ammo caches to collect at different points in the game, as well as 333 antlion grubs to squish, but with the exception of the “Gordon Propelled Rocket” cache, none of them are anything special. (On a quasi-related note, The Orange Box has the greatest suite of Achievements of any game.)

We’ve covered several different aspects of level design already, but we’ve really only scratched the surface. Next week we’ll discuss pacing, difficulty curves, scripted events, puzzles, and enemy placement.

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