the artistry and psychology of gaming


The Architecture of Half-Life 2 (Part 2)

The Architecture of Half-Life 2 (Part 2)

Hello and welcome to Part 2 of our discussion of level design and how Half-Life 2 does it well. In Part 1, I explained and analyzed topography, mission objectives, and hidden collectibles. This week we’re getting a little bit more specific and looking at some of the finer details of level design.


Regardless of whether you’re talking about video games, cinema or television, not every scene has the same mood. Some scenes are calm and quiet. Others are loud and action-packed, at times becoming chaotic and bombastic. Still others have less action and noise, but are still suspenseful and disquieting. Pacing is the art of managing and balancing all of these moods. If there isn’t much excitement, tension, or intrigue, a game can get to be tedious and boring. I felt that Assassin’s Creed suffered from this, as did the beginning of The Legend of Zelda: Twilight Princess. On the other hand, if a game is nothing but chaos and bombast with no reprieve, as is the case with Call of Duty: Black Ops, then the player can get frustrated and burned out. Keep in mind that it is still possible to make a “non-stop thrill ride” game or movie and still maintain an intelligent sense of pacing. For instance, most of the movie Speed takes place on a bus that will explode if it goes slower than 50 miles per hour – it is literally a non-stop ride – but it still has much better pacing than most action films.

The key to great pacing is to follow a “build up/release” formula. Over a period of time, build up tension, and then periodically release the tension through some sort of resolution. Each conflict doesn’t necessarily need to be resolved before moving on to the next one; compounding problems can work really well if handled deftly. Also, overall tension should increase throughout the game until the climax – though putting a big set piece at the beginning to grab the audience’s attention is a good idea as well. Since story-based video games generally take much longer to complete than a movie, there is definitely some room to play around with this formula, and just like any guideline for making great art, spitting in the face of convention can be just as effective if done correctly.

Pacing is one of the areas in which Half-Life 2 really shines. The game is divided into a number of distinct sections, usually (but not always) contained within their own named chapter. Each section gradually builds in intensity, culminating in a spectacular set piece, after which there is typically a relatively tranquil stretch of gameplay. One or two smaller set pieces are also spread throughout most segments for variety.

For an example, consider the Water Hazard chapter, early in the game. The entire thing (along with the previous chapter, Route Kanal) is basically a giant chase scene, with Gordon Freeman trying to escape the forces of the evil Combine. After some running and gunning in Route Kanal, you get an airboat for the Water Hazard chapter. But now, in addition to the submachine gun-wielding mooks you’ve been fighting previously, a bunch of armored vehicles show up to launch rockets at you. Unfortunately, you cannot use any of your weapons while piloting the airboat. Several times you must leave your vehicle to clear the way forward, and during one of these detours, a helicopter (the Hunter-Chopper) will begin harassing you as well. So for a few minutes, you are tasked with dodging submachine gun fire, rockets, air-dropped mines and barrages from the Hunter-Chopper’s automatic pulse cannon. This is the tension-building part.

The resolution occurs late in the level, after some friendly rebels give you an airboat-mounted pulse cannon of your very own. Shortly afterward, the Hunter-Chopper shows up again, and a showdown ensues. It would be easy enough to program the game in such a way that Gordon Freeman simply ducks into a cave and eludes his pursuers for the time being, but that is far less satisfying than a boss fight that lets you exact your revenge on the helicopter that has been hounding you throughout the level. (In fact, there’s nothing keeping you from running to the valve that opens the door out of the boss arena; it’s just that the Hunter-Chopper will fill you with daylight as you try to open it.) Instead, Half-Life 2 treats you to an explosive encounter between two heavily-armed vehicles. Once you’re done with that, there is a brief plot-based section, giving you the opportunity to cool off.

And if this “build tension/release tension” formula sounds familiar, get your mind out of the gutter. But that’s totally why it works so well.

Difficulty Curve

Tied closely to pacing (as well as several other aspects I will mention later) is the difficulty curve of a game. Ideally, the beginning of a game should be easy enough for a newcomer to pick it up and play, but not so easy that it puts veterans to sleep. After that, there will be a series of peaks and valleys, though the overall difficulty should increase fairly steadily. The peaks line up with the large set pieces and boss fights, and the valleys represent the parts after the set pieces that either provide the player with a sense of empowerment or are simply calm segments that let you catch your breath. The ending should be a test of whether the player’s skill has increased over the course of the game; a neophyte should not be able to survive for very long. In fact (MATH ALERT!), if a difficulty curve was represented as a mathematical function, and the player’s increasing skill level was also represented as a function, subtracting the latter from the former would result in a graph resembling a shallow sinusoidal wave hovering slightly above the x-axis. (MATH ENDS HERE) If there are any bonus levels after the credits roll, these can (and in my opinion, should) be maddeningly difficult. This gives hardcore fans something to work on after the game is completed (other than multiplayer), and the difficulty won’t frustrate more casual players because the bonus levels aren’t required to complete the game. Even if a game is designed to make you cry (like Super Meat Boy or Demon’s Souls), it should still have a similarly-shaped difficulty curve, just placed higher on the graph.

For any game developed by Atlus, adjust the scale so that “Nigh Impossible” is at the bottom and “ALL JOY HAS LEFT MY SOUL! WHAT DID I EVER DO TO DESERVE THIS?!” is at the top.

Out of all the games I’ve played, there are only two whose difficulty curves I would describe as “perfect.” While neither of them are Half-Life 2, the game still boasts one of the smoothest curves in the industry. The challenge increases at a similar rate to the ideal graph pictured above, though there are no bonus levels… unless you choose to attempt a self-imposed challenge. (Bullets are for sissies! True badasses only use the crowbar and Gravity Gun!) The one bit of schizophrenic difficulty occurs during the second turret battle in the Entanglement chapter (AKA the “Warden Freeman” fight), which seems a lot more difficult than anything preceding it, as well as anything else before the end of the game. Thankfully, there are clever (read: cheap) ways of turning that skirmish into a cakewalk.

Scripted Events

What are scripted events? Allow me to explain. Scripted events are incidents which always occur when the player activates a certain trigger, such as a zombie dog jumping through a window or a building starting to collapse while you are still inside of it. They exist in a gray area between cutscenes and gameplay. Scripted events differentiate themselves from cutscenes in that you typically don’t lose control of your character while they are happening. However, they don’t fit into the category of normal gameplay because they won’t happen until you set foot in a trigger area or let a timer run down; that zombie dog just doesn’t have advanced enough AI to leap through a plate glass window (and make you soil yourself) whenever it pleases. If utilized correctly, scripted events can move the plot along without interrupting gameplay. They can also make a game less predictable and more exciting on a first playthrough. While they make a game more predictable on repeat playthroughs, they’re still exciting because it means that Awesome Stuff™ can happen without forcing you to watch a cutscene. Scripted events also help the game world feel more “real” and immersive.

The original Half-Life was a pioneer in the field of scripted events. It wasn’t the first game to use them, but few previous games had used scripted events as extensively, or as effectively. This is largely the result of difficulties that the designers faced early in the development cycle. Originally, the levels they designed felt empty and boring. In desperation, the developers made a single level and populated it with every enemy, every weapon, every scripted event and every quirk that they had created thus far. That single level inspired them to continue development of the game, and the studio completely reworked everything they had made to that point. As a result, the finished game is full of numerous scripted events, such as monsters knocking down doors and Black Mesa employees being dragged into air vents. In addition, the story is told almost exclusively through scripted events; the player rarely loses control of Gordon Freeman.

Half-Life 2 upholds the tradition of high-quality scripted events, with events that are even bigger and more spectacular. One oft-cited example occurs in the Water Hazard chapter when a stray rocket hits a gigantic factory chimney, causing it to crumble and fall directly into the path of your airboat. If you have quick enough reflexes, you can steer through a gap in the wreckage, or perhaps use a chunk of the chimney as an impromptu ramp.

“Oh crap.”


Puzzles are a nice way to add a little variety to a game, allowing you to give your reflexes a rest and let your brain take over for a while. One way to design a great video game puzzle is to be clever about it, making the player think outside of the box (or look up a walkthrough on the internet) or simply presenting it in a way that isn’t seen very often. The better puzzles in the Silent Hill series are great examples, like the noose puzzle in Silent Hill 2 (“Only the sinless one can help you here.”) or the hospital keypad puzzle in Silent Hill 3 (“I place my left hand on your face as though we were to kiss. Then I suddenly shove my thumb deep into your eyesocket. Abruptly, decisively, like drilling a hole.”). Another way to design a great video game puzzle is to integrate it organically into the game’s environment. What I mean by that is that all of the components of the puzzle are things you would logically expect to see in the game’s setting, and the solution (while it may not be immediately obvious) does not violate common sense. Moving a large box so you can climb up to a higher ledge is an organically-integrated puzzle, particularly if you are in a warehouse at the time; defeating a robot in a game of chess to make a set of stairs appear from nowhere is not. Most of the puzzles in the God of War series are organically-integrated. (Let’s just forget about the terrible Guitar Hero-style puzzle in God of War III, shall we?) Once in a blue moon, you may even play a game in which the puzzles are both clever and organically-integrated, like Portal 2.

Half-Life 2’s puzzles fall squarely into the “organic but not terribly clever” category. A majority of the puzzles are based on the physics engine, and you will soon notice that most of them are variations of a simple lever puzzle. However they did manage to squeeze a lot of mileage out of the concept; the gigantic unstable bridge in the Freeman Pontifex chapter of Episode Two is particularly impressive. All of the puzzles also work successfully and smoothly with surprising consistency: puzzles reliant on the physics engine in other video games tend to be a hit-or-miss affair. And while you may tire of dealing with fulcrums and leverage, at least Half-Life 2 will never ask you to rearrange soup cans to unlock a door.

Hey, The 7th Guest, can you unscramble this? CFKO UUY!

Enemy Placement

Enemy placement encompasses a few different facets, including the physical locations of the enemies in the level. Placing just one standard enemy in a large arena with lots of room to maneuver seems like a waste, and cramming half a dozen Elite Deathbringers into a tiny claustrophobic chamber probably isn’t a good idea either (unless you are designing the Bonus Dungeon). Also, placing a baddy in a location where they have a clear advantage (like behind a mounted gun, for instance) can add depth to gameplay and keep the game from becoming a mindless button-mash-athon. The above example may require that the player use the environment as cover to close distance, or they may need to find a way to flank the enemy.

Another factor to consider is enemy variety. No one wants to fight the exact same adversaries throughout the entire game, so developers should mix and match enemy types as you progress. Particularly clever dev teams may group monsters together in advanced levels in such a way that they complement each other and account for each others’ weaknesses. For example, an enemy with a powerful but slow attack may be paired up with a swarm of tiny enemies that can impede your movement if you don’t dispose of them.

Unsurprisingly, Half-Life 2 nails this aspect of level design as well. Enemies are often arranged in a way that perfectly balances run-and-gun gameplay and tactical planning. The “guy behind a mounted gun” scenario occurs a couple of times, and you’ll also find yourself figuring out how to gain the upper hand over snipers, automated defenses, and gigantic biomechanical weapons that are immune to everything short of explosive firepower. Fighting anything in that last group (Striders and Gunships) usually involves avoiding their attacks until you stumble upon a cache of rockets, since you can only carry a limited amount of RPG ammo on your person. There is a wide variety of distinct enemy types, with many getting their own “holy shit!” moment the first time you encounter them, and towards the end of the game they do indeed begin working in concert. Episode Two culminates in a battle against 13 massive Striders, each accompanied by a cadre of smaller Hunters, and the symbiosis formed between them is one of the most beautiful and terrifying in gaming.

Tangentially-Related Fun Fact: The Combine Gunships do not possess independent AI. Instead, each one follows a series of predetermined paths through the air. This makes their flight look more natural, and ensures that they don’t engage in random AI shenanigans like getting stuck in walls or hiding in awkward places.

While variety is nice, Half-Life also benefits from the designers recognizing that a degree of homogeneity is called for at times. Limiting the number of enemy types for a single level can be extremely effective if variety is used throughout the remainder of the game. Obviously you aren’t going to see very many aquatic enemies in a desert level, and if you’re invading the main base of Faction A, there won’t be anyone from rival Faction B defending it, but being selective with enemy types can be done for gameplay reasons as well. For instance, shortly after acquiring the Gravity Gun at Black Mesa East, you must navigate through the zombie-ridden town of Ravenholm. The story provides some justification for why you’re fighting through a miniature zombie apocalypse at that point, but it’s really just a detour and could logically take place at just about any point in the story. (In fact, the Ravenholm chapter originally preceded the Black Mesa East chapter.) The real reason why Valve sends you to a level filled with headcrabs and zombies immediately after giving you the Gravity Gun is that neither of those enemies have projectile attacks, giving you some time to have fun with your new toy*. Similarly, towards the end of the game, you attain a weapon that is incredibly powerful against human enemies. For the rest of the game, the enemy forces are almost exclusively comprised of footsoldiers. To preserve the challenge, they send scads of guys after you, which also contributes to the climactic feel of the level.

If you happen to be one of the people who made L.A. Noire, take note: this is what you do after giving us an awesome weapon. You shape the following section of gameplay in a way that lets us have fun with it. You do not, say, give us a flamethrower and then send us through several extremely large rooms where the people shooting at us are always just out of range and flowing water slows us to a walking pace, while preventing us from taking cover or switching back to a more reliable gun.

*Editor’s note: The Zero Point Energy Field Manipulator is not a toy!

Believe it or not, we still aren’t quite done with Half-Life 2. Next week, I will conclude this inaugural installment of The Architecture of Gaming by covering the subjects of aesthetics (particularly atmosphere and world building), disguising technical limitations, variety, guiding the player, and freedom.

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