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Developer commentary/Half-Life 2: Episode One

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This article is a transcript of all of the quotes from a given character or entity. Unless noted otherwise, these transcripts are sourced directly from the official scripts, closed captions, or internal text data with only minimal modifications for typos and formatting purposes.

The following is a list of all of the developer commentary from Half-Life 2: Episode One's commentary mode.


Filename Speaker Subtitle
intro Gabe Newell Welcome to Half-Life 2, Episode One. We received a great deal of positive feedback on the commentary track in The Lost Coast, and so we've included the same feature in this episode. To listen to a commentary node, put your crosshair over the floating commentary symbol and press your use key. To stop a commentary node, put your crosshair over the rotating node and press the use key again. Some commentary nodes may take control of the game in order to show something to you. In these cases, simply press your use key again to stop the commentary. With episodic content, we are hoping to release games much more frequently than has been possible with the monolithic development schedules of the past. Game developers and game customers have been wanting to try this for years. Please let me know what you think after you have had a chance to play this, our latest installment in the ongoing adventures of Gordon Freeman. I can be reached at Thanks, and have fun!
intro_design Greg Coomer This intro sequence establishes some important initial pieces of Episode One's story and setting. Our earlier versions of the intro sequence were heavy on graphic effects and relatively light on storytelling. When we showed those early versions to playtesters, they thought it was cool, but rarely had any idea what was supposed to be happening. We went through several iterations, each time simplifying the editing and tightening the effects. We eventually arrived at a good middle ground between the sort of psychedelic look we were shooting for and basic comprehension of what was actually taking place.
citadel_skybox Jay Stelly The Citadel is supposed to be a building of unprecedented scale - so out of scale with the rest of the world, in fact, that we couldn't render it without our 3d skybox technology. This technology allows us to build the Citadel as a 1/16th scale model off in an unreachable corner of the map and seamlessly merge it into the scene. We also use this technology to create the illusion of vast spaces and distant horizons.
monitor_scene Marc Laidlaw Right off the bat, we needed to hammer home some story points, reintroduce the cast of characters, and explain the player's immediate goal. It was a pretty intimidating chunk of non-interactive exposition. We generally approach these scenes by writing way too much, and then, through constant playtesting, trimming the scene to more manageable levels. In this case, even after some heroic pruning, the opening scene still felt too long. We ended up splitting the introductory sequence into three scenes, separated by some gravity gun puzzle solving and then a dramatic walk across a crumbling ledge.
dog_dropship Bill Van Buren Sometimes, we need to keep the player in an area so that we can deliver some critical dialog or run an important sequence of events. In these cases, we temporarily block the player's path using what we call a 'gate'. These gates generally take the form of some obstacle that can only be removed or opened by some character or event. In this case, the obstacle is a crashed gunship that can only be moved out of the way by Dog. Though the final scene looks pretty straightforward, a lot of care had to be taken to make sure that Dog hit his marks and played his sequences without trampling and damaging the player.
alyx_ledge Robin Walker This ledge is a really tricky spot for NPCs to navigate. While we wanted Alyx to be able to maneuver dynamically through any complex environment, in certain navigation situations we're faced with a trade off between flexibility and visual quality. In this particular case, she navigates this ledge with a combination of AI and scripted animations. We continue to evolve the systems of Half-Life 2 whereby characters move fluidly through dynamic AI and scripted navigation, but ultimately what matters most is how it looks to the player.
falling_debris Matt T. Wood Since we never take control away from the player, it can be a real pain to get them to notice important environmental events. It's a constant design challenge for us. The Citadel will be erupting in a massive light show that took ten of us two months to orchestrate, and, if we're not careful, the player will end up facing the other direction staring at a tire. In this case, to establish that the Citadel is coming apart at the seams, we wanted the player to notice the debris falling off of it. We used a pretty straightforward method here - Alyx explicitly mentions the citadel while pointing at it. Like most of these solutions, it's not foolproof, but it has a high success rate.
dog_throw Bill Van Buren Our games are created by design collectives that we call 'cabals'. When the idea to have you and Alyx sit in a van and then have Dog toss it across the gorge was first suggested during a cabal meeting, everyone thought it was funny - and then we moved on to more serious solutions for the gorge crossing. As the design progressed, though, we kept coming back to the van idea, and eventually everyone agreed that we should give it a try. Even though the idea was kind of outrageous, it satisfied some key goals we had for the scene: Alyx and the player get across the impassable gorge and Dog is able to play a key role in the mission while also plausibly getting left behind. There were still some problems to solve, though: attaching animated models to the van was tricky, making sure the van didn't kill the player took some thought, and it took a number of tries before we were able to really illuminate Dog's thinking, as he went from testing his idea with chunks of debris to finally presenting the plan to Alyx. Ultimately, we were able to create a scene that solved some tricky game design issues, provided an intimate view of the relationship between Alyx and Dog, and delivered a surprising and visceral entrance to the Citadel.
youdidthemath Yahn Bernier It's really important to us to create scenes that showcase strong relationships between our characters. The relationship between Alyx and Dog seems to be especially satisfying to players. In the scene leading up to the van toss, we had a bug before the animation was complete where Dog's head would shake as he looked back at Alyx. In a happy accident, his head shook right after she asked him, 'You did do the math, right?' In playtests, players thought this was intentional and always laughed. Because of that, we worked it into the animation and it ended up being a terrific little moment between Dog and Alyx.
alyxnag Matt T. Wood To convey a sense of urgency, we originally designed Alyx to nag the player pretty frequently. She'd say things like 'Hurry up!' and 'Keep moving!' Whether or not this created a sense of urgency is debatable. But after about three minutes of this, the one thing it definitely did was make the player hate Alyx. This was one of the observations that eventually led us to switch Alyx from generally leading players to almost always following. Through playtesting we discovered that players much preferred to set the pace themselves and that they especially disliked virtually any hint of bossiness from Alyx.
alyx_specular Jason Mitchell Alyx travels through much of Episode One with the player and consequently passes through a wider variety of lighting conditions than she did in Half-Life 2. This meant that we had to improve the quality of the lighting algorithms used on Alyx to look realistic in any situation, from the eerie hallways of the Citadel to the streets of City 17 at sunset. For this episode, we added a specular lighting term to the shaders used on Alyx, which provides a realistic shiny look to her skin, her leather jacket and even her teeth. In these new lighting calculations, we chose to specifically emphasize bright highlights caused by illumination from grazing angles. This type of lighting, also referred to as 'rim lighting' is particularly dramatic when coming from low-angle light sources such as this bright sunset. You'll also note that the rim lighting is further enhanced by our high-dynamic range postprocessing, which causes the specular highlights to bloom in a striking and dramatic fashion. We have found that the move to an episodic development cycle allows us to take advantage of the fast pace of graphics hardware innovation by incrementally adding new features, such as Alyx's new lighting techniques, to the Source engine with each new episode.
intro_effects Gary McTaggart We used an upgrade of the refract shader from Half-Life 2 to make the Vortigaunts warp into the intro. The major difference is that this time we are refracting only pixels that come from the Vortigaunts themselves. We placed a large sheet of refractive geometry in front of each Vortigaunt to achieve this effect.
charactersys Ken Birdwell When we designed the Half-Life 2 facial system back in 2000, our goal was to get a natural looking performance at a moderate distance. Given our realtime polygon and texture budgets, we chose fairly reserved or constrained performance over ever having the actors faces get into a bad looking or unnatural expression. For Episode One, we wanted to extend the characters' facial systems to support more intense performances with a wider range of facial expressions, that would hold up better at close range. These facial improvements included increasing the detail around the eyes and mouth, increasing the number of facial shape targets - think of these as movements of muscle groups - by about 50%, rewriting the rules that control how these shapes blend, and increasing the intensity of many of our existing shapes. In addition, we added support for controlling the amplitude of the facial movement for lip-sync animation, which let us dampen or amplify the mouth shapes based on the volume or intensity of the dialogue.
dogmyhero Bill Fletcher Players love Dog, so we made sure that he was the first thing you see when you wake up in Episode One. We also wanted players to get a glimpse of the crippled Citadel. When Dog lifts you out of the rubble, it's one of the few instances in the game where we take control of the player's view. This allowed us to ensure the player's view lingered briefly on the Citadel before Dog set them down.
justhavetodoit Matt Scott This area was redesigned several times in order to keep the player in this space while Alyx delivers some exposition. As much as we hated to do it, the final solution was to have Alyx climb out while the player looks for an alternate route. We portray Alyx as more athletic and nimble than Gordon, so the player shouldn't get too irritated by the fact that she can get to places they can't. Honestly, we're not especially happy with this crutch, but it's a trade-off we sometimes have to make so that we can get Alyx out of the way of interesting player challenges.
monitorscene Bill Fletcher Monitor scenes are especially difficult to make interesting, since they tend to involve literally just talking heads. By interweaving critical expository information - like how dangerous the Citadel has become - with some dramatic character interactions between Alyx, Eli, and Dr. Kleiner, we were able to convert a potential liability into one of the strongest scenes in the game. A great way to illustrate characters' relationships to each other is to have one of the characters in danger and show the others' reactions to it, which is what this scene is all about.
firstvista Charlie Brown We populate our environments with spots where players can take a break to look out over an expanse of cool scenery. We call these 'vistas'. This particular vista was designed to give anyone familiar with the Citadel interior from Half-Life 2 a good view of what it looks like now that everything's falling apart. The pods that are sliding off their track and into the abyss really sell the idea that the Citadel is half-abandoned and in chaos.
alyxconsole Matt T. Wood In an early version of this map, Alyx led the player through the whole thing. To make Alyx seem less omniscient, we had her access a console here to 'get her bearings'. It exploded, which helped drive home the point that the Citadel was in bad shape, but, generally, it was a long pause in the action without a lot of payoff. After we made the high level decision to have Alyx follow the player, this entire scene became irrelevant, and we happily cut the whole thing.
rollertraining Matt T. Wood Training is one of the fundamental tenets of our design philosophy. Before the player is required to utilize some new game mechanic or new weapon, or face a new monster under pressure in a dangerous situation, we always introduce the concept in a relatively calm but ideally still entertaining way. This entire scene teaches the player that Alyx can convert rollermines so that they can be used as a friendly weapon. Later, the player is required to do this in more pressing circumstances, but at this point everything's still pretty calm. In the original design, the player retrieved a rollermine from a dispenser and used it to take out a Combine soldier who was holding the field from the other side. Eventually, we scrapped that idea and combined the rollermine training with some stalker exposition that originally occurred in a separate scene.
rolleradventure Steve Bond In a good puzzle, the player is presented with an overall goal and then faces a number of smaller challenges in pursuit of that goal. In the case of the Stalker puzzle, we start with 'How do I open the door?' From there we move to 'How do I get to the Stalker?', then to 'How do I get to the rollermines?', 'How do I get the rollermine back to Alyx?', and, finally, 'How do I use the rollermine to disable the stalker?'
vortexoflove Matt T. Wood The primary goal of the first Citadel map is to communicate to players that the Citadel is falling apart. The vortex was a late addition to the map in an effort to beef up the idea that the Citadel was becoming a very dangerous place. We had particular difficulty in conveying the 'danger zone' here. In early playtests, players thought that the entire bridge was dangerous at all times. Some additional effects work helped let players know where the dangerous areas were. We would have loved to base more gameplay on this vortex idea, but we just didn't have the time.
podroomlook Randy Lundeen We decided this space needed to look unique and appear to have more significance than the rest of the Citadel areas the player had already traveled through, while at the same time feeling as though it was still made with Combine technology. This room introduces a story point that plays a big role in Episode Two, so the player has to feel like something important is going on in here. A different fog setting as well as different light styles and configurations helped achieve this. The red lighting is a good contrast to the traditional blue/green colors of the Citadel.
podrising Ted Backman We revealed the pod here to let players see it up close. At the same time, we didn't want the player to get too good a look at what's inside. An old version of this scene had the pod simply hanging from the ceiling. It would burst open and then charge up your gravity gun, but not do much else. The current scene gives us a much more dramatic reveal of the pod and an opportunity to introduce the mind blast it's capable of emitting. Though they don't play a large role in Episode One, these guys were a functional requirement of Episode Two, which meant we effectively had to ship a piece of that episode early.
citadellook Randy Lundeen We created a new Citadel destruction set of 'broken' Combine panels and prefabs for the interior spaces to help make the Citadel look like it was on the verge of exploding. We also introduced a strong ambient orange color to help sell the fact that the Citadel was in a much different state from the last time the player passed through. The orange atmosphere was justified due to all the fires and smoke inside the Citadel.
alyxcitadeltone Bill Van Buren We wanted to create an atmosphere of urgency in the Citadel, with Alyx and the player focused on getting to the core to stop the impending collapse. Initially, we tried to reflect that urgency through Alyx's behavior and acting. This proved to be unsustainable, however; if the player didn't choose to advance, Alyx eventually ran out of lines or animations and was forced into her very non-urgent idle states. We found that the best approach was for Alyx to have such implicit trust in, and sympathy with, the player that she is always content to proceed at whatever pace the player chooses. Once we adopted this principle, lines where Alyx sounded impatient or frustrated with the pace of progress quickly stood out and were cut.
whatwasthatthing Keith Huggins It's important that the player has some empathy for Alyx, rather than just seeing her as a bullet-spitting robot. The brief recovery scene after the pod mind attack reminds the player that Alyx is affected by events in the world.
3stepapproach Scott Dalton The light bridge ball sockets are a clear example of our training approach to new gameplay elements. We train players with a leading example, confirm they understand the concept, then switch up the problem set and make them use it in a new way. The first bridge shows players the solution, the second one confirms they understand, the third, knowing they understand the gameplay mechanic, challenges them in a new way using that mechanism.
puzzlerefinement Scott Dalton Having trained the player that balls fit into sockets, we wanted to introduce a puzzle where the question was HOW to get the ball into the socket. The puzzle we came up with involved a socket with an object blocking it, so that the player would have to ricochet the ball into place. That sounded simple until we actually tried to implement it. If we made the covering opaque, playtesters didn't realize that there was a socket behind it. When we made it translucent, they often didn't see it was there and were confused when their shot bounced off. Making it movable was a red herring making people think they could knock it away. A couple of subtle art changes helped. We added some more prominent shadowing and made the glass panel flash whenever it was hit with a ball. Some playtesters consistently searched for a position to get a direct shot, which we didn't discourage as an alternate solution.
citdestruction Scott Dalton Impending destruction is a recurring theme in the Citadel. From story, mood, and visual standpoints, this changes the Citadel. The destruction needed to feel natural rather than entirely scripted on the player's actions. Not showing the destructive events dynamically makes the player assume the level of damage is static. However, if the events are too obviously triggered by player movement, the destruction feels too scripted. We found the solution was to give the player glimpses of things happening at the periphery of the player space, as well as in their immediate vicinity, to give the feeling that this stuff is happening whether the player is present or not.
drawingattention Brian Jacobson This dropship scene was another case where we had to be clever about drawing the player's attention to something cool that was about to happen, which the player could easily miss if they weren't looking in the right direction. We used a solitary soldier firing at the player to draw their attention to where the dropship climbs into view. Once the player notices the dropship, there's a good chance they'll watch it until the payoff when it crashes.
alyxrunspeed Doug Wood There are some little practical details that take a surprising amount of time and testing to get just right. For instance, it took us many playtests to figure out how fast Alyx should move. It turns out that her following behavior looks and feels the best when she's moving faster than the player's normal speed, but slower than the player's sprint speed.
puzzlearc John Guthrie This is where some player training pays off. After earlier training players on the use of ballsockets, they get a sort of 'live fire' test here starting the elevator. This is the beginning of this level's puzzle arc, where a basic gameplay mechanic is made increasingly more complex by layering other puzzle elements on it. This first puzzle only requires that the player find a combine ball and put it in the socket.
stalkerball John Guthrie Here we're presenting the player with a now-familiar ballsocket challenge, but we're also bridging into some new training, showing the player that Stalkers can destroy the Combine energy balls.
coredoors John Morello Late in development, we changed the art for these doors so that players understood that they were entering the core area. It turned out that having Alyx talk about the area wasn't enough to give playtesters the sense that they'd finally arrived at the core.
ohmygod Doug Wood This is another key vista - this time showing the core. It's a visual payoff for the player's success in getting here and, simultaneously, a way to present the player with a view of the next challenge.
whereisshe Doug Wood Monitor scenes, such as this video transmission from Dr. Mossman, aren't simply prerendered video. These scenes actually unfold live in an inaccessible section of the map, while being projected onto the monitor screen. Here's Dr. Mossman in the small arctic base set. It's not nearly as far away from the Citadel's core control room as it appears to be in the level.
thecore Dhabih Eng The core design posed a lot of difficult challenges. Generally speaking, if the gameplay in a particular map isn't working, we can simply cut the entire area. That wasn't true of the core, because we knew it was critical to the story. On top of that, designing Citadel gameplay is often a bigger challenge than working out areas in City 17, largely because Citadel levels have a narrower set of gameplay tools; There are less enemy types available and the player is usually only armed with the gravity gun. Because of this, we had to go through many iterations of the core design. One of the early prototypes was a kind of futuristic version of 'Operation' where players had to use the gravity gun to cleanly manipulate rods into slots in the core. That didn't work partly because playtesters found that their view was obstructed by the rods, which made it frustratingly difficult to manipulate them with any kind of precision. We prototyped, playtested, and abandoned several other designs until we finally arrived at one that was fun while still being challenging enough to give players the sense that they'd accomplished a significant goal.
coresphere Gary McTaggart The core sphere was one of the last special effects that we finished. To achieve its effect, the core uses animated textures, flowmaps, normalmapped refraction and specularity, as well as volumetric particulate matter rendering, which takes advantage of the core being a sphere.
corecolorscheme Randy Lundeen The higher contrast white Combine motif of the core sets it apart from the rest of the Citadel and heightens its importance within the visual style of Combine aesthetics. It also helps enhance the sense of heat and radiation in the space.
balltubes Scott Dalton The ball tubes are an example of us working within our available toolkit to create a puzzle around a recognized concept. As a physical navigation puzzle, it's different from what the player has experienced before, and it's challenging while not being a binary succeed or fail situation. There are a number of ways to approach this puzzle. In addition to simply dodging, jumping and ducking the balls, the player can grab or deflect them with his gravity gun, or pick up the hatch and use it as a shield to block the incoming barrage.
corepaths Greg Coomer The core was a central element of this part of the game, and, as much as possible, we wanted to constantly reinforce its importance. Zigzagging through the space in three dimensions while navigating a variety of challenges let us present a few different visual and gameplay perspectives on the same space. By letting the player see the core from a bunch of different angles, we were able to give them a real sense of its scale.
secondballtube Scott Dalton The second ball tube presents a variation of the pattern the player learned in the first ball tube. While the first tube can be crossed slowly by crouching and maneuvering your way up, the second ratchets up the pace, requiring a quicker, more responsive approach.
finalcontrolroompuzzle Scott Dalton The goal of this logic puzzle isn't figuring out that you need to put balls in the batteries, it's coming to the realization that by filling all of them, you've denied yourself an exit, and that you have to desocket one, climb on the lift, and then resocket it. Sparks guide the player to the source of the balls, which happens to be the tube they just passed through.
skilllevelchange Steve Bond The difference between skill levels isn't just a matter of damage dealt and received. For instance, in easy mode, we increase the length of time a Combine ball survives before exploding, putting less pressure on the player to get the ball into a socket.
combinecorelook Dhabih Eng The Combine core was another new space that needed to stand out from the rest of the environment. We wanted the core to look hot and dangerous, but still be distinct from the fires and the cool blues of the rest of the Citadel. The core became the primary light source in this space and in conjunction with the white set of Combine materials, we created an extreme contrast with the normally dark values of the Citadel metals.
hurryback Bill Fletcher Creating a believable, interesting relationship between Gordon and Alyx is made a lot tougher by the fact that Gordon never talks. This elevator scene presented a nice little opportunity to have Alyx express some emotion in a situation where Gordon isn't really in a position to respond.
hackingrollers Matt T. Wood Usually, the second step of our training arcs involve a threatening training area. This is the second step in the rollermine training, and true to form, there's a threat. The indestructible rollermines endlessly attack the player in a gated space. The only way to defeat them is to have Alyx convert them, which means there's no way the player can miss the point of the training. Players also like to see the AI characters fight each other, so after reminding the player about Alyx's rollermine hacking talent, we let you sic them on a pack of Combine soldiers.
stalkertrainmodels Matt T. Wood In much the same way that movie effects often utilize different versions of the same model, there are actually three trains that make up the stalker scene. The first one is the moving train you see arrive at the platform. The one you're in right now is a static interior with lights moving outside of it to give the illusion of motion. The third train is the crashed version. It's a tilted, banged up, and totally separate area from the moving version. The transition from moving to crashed is disguised by a brief fade to black.
crashedstalkercar Matt T. Wood We wanted the crashed train car to be very disorienting. In early tests, though, players felt that it was too confusing and too hard to navigate. That feedback prompted us to tone it down a bit. By rearranging some of the geometry, we were able to create a banged up, tilted environment that still offered a relatively unobstructed path to Alyx.
stalkeriteration Bill Fletcher Alyx's reactions to the Stalkers went through a number of iterations. In very early versions, Alyx was frightened by the Stalkers. That didn't work because it didn't fit with Alyx's earlier reactions to Stalkers in the Citadel. We changed it so that she expressed anger at the Stalkers' predicament. Early versions of this new direction failed because Alyx's transition from generally upbeat to blind rage was simply too abrupt. Ultimately, through rewrites and rigorous testing, we found the right tone for the scene - a simmering anger level that was more in tune with the situation.
holdupasec Bill Fletcher This is another multipurpose scene. First, Alyx is visibly shaken, which once again humanizes her. But she also states the player's goal for the second half of the game: climb to the surface and get to the train station.
flashlightgameplay Steve Bond Initially, the player wasn't going to have a weapon here. The combination of no weapon and near total darkness forced the player to use the flashlight to direct Alyx's fire. We liked the idea that you could interact with Alyx in a meaningful way using elements that were already built into the interface. Unfortunately, playtesters didn't like not having a weapon. So we added weapons back in. Luckily, it turned out that, even armed, players tended to still use and enjoy the flashlight mechanic.
weaponpickup Jim Dose Before we armed players with traditional weapons, we wanted to give them a chance to appreciate Alyx's combat abilities. Toward that goal, we created a very specific combat style for the early parts of the journey outside the Citadel - dark, tense, surrounded by zombies, and either weaponless or starved for ammo so that players needed to rely on the gravity gun and, more importantly, Alyx. This is where players finally get a weapon. Since the door only opens when the padlock is shot, players can't proceed without finding the pistol. It's effectively a weapon gate - once players are through the door, we can be sure they've got a pistol.
powerboxes Jake Nicholson Originally, the player couldn't operate the power boxes and would have to wait for Alyx to do it. We thought it'd be entertaining to watch Alyx do some cool thing while you protected her. Unfortunately, that didn't work out. Playtesters were more annoyed than entertained. The other problem was that having Alyx committed to a particular activity while action was still going on in the world tended to quickly expose her most robotic tendencies. She'd either ignore what was going on or completely stop whatever activity the player was waiting for her to finish. Either way, it was unconvincing and frustrating. We learned that whenever Alyx commits to some action in a dynamic environment, she needs to finish it quickly and move on.
benefitsofdarkness John Guthrie The darkness in this area has a few real gameplay benefits. It slows the player down, which most of the time keeps Alyx at your side. The claustrophobia, the close in combat, and Alyx's constant presence and reliance on your flashlight help enhance the tension and your sense of camaraderie. In the dark, the limited flashlight battery adds an extra layer of resource management to the tactics of combat.
likeablealyx Erik Wolpaw If you don't like Alyx, you're not going to have much fun with Episode One. So Alyx being likeable was one of our most crucial design goals. Little moments like the Zombine joke are designed to make Alyx more endearing. Since we like to multitask, it also had the practical purpose of introducing a new monster. The success of the scene relied on a combination of dialog, voice acting, and animation. Surprisingly, lighting was really important too. Under red light, Alyx's self-deprecating groan looked more like she was sneering at the player for not getting the joke. Changing the lighting to blue and then adjusting the direction of the light so that it changed the shadows on her face fixed the problem.
monsterintro Adrian Finol It's important that monsters get very deliberate introductions since players are going to interact with them a lot. Generally, we let the player first see a new monster in a safe environment, so that they can start thinking about it before they have to fight it.
zombinemusic Kelly Bailey The soundtrack here was created for the introduction of a new adversary, the Combine zombie, or Zombine. Dischordant guitar tones and bends, and a low-fi, fast beat work in the background of this encounter to create an off balance and disturbing mood.
responserules Jim Dose For Episode One, we implemented a scripting component, called the 'Response Rules System', for dynamically managing NPC speech. We wanted to take NPC speech out of the hands of the programmers and let the writers control it. The writers were able to set up a wide range of situationally triggered character responses. For instance, Alyx has different reactions to different enemies, can warn the player of danger, calls for help when she's mobbed, and will ask for light. The combat responses worked out great, but it's especially satisfying when Alyx's comments on some situation mirror your own thoughts. The writers really went crazy with this, so be on the lookout for lots of little easter egg responses to unusual situations.
flares Robin Walker We always try to exploit a feature as much as possible throughout a game. For instance, these flares. They're an exploration reward, they've got a simple, satisfying interaction with the gravity gun, and they're a good tactical alternative to the flashlight. Finally, they're a weapon that will ignite zombies, which in turn become a new light source.
poisonambush John Guthrie Poison headcrabs are ideal for ambushes, because they startle you, but can't actually kill you. Here, after a series of right hand turns, you round a corner into a dead end. While you're cracking open a box of goodies, you're ambushed by a poison headcrab. Constructing the ambush this way increased the odds that you wouldn't see the crab, but would hear it just in time to turn around as it leapt at your head.
holetraining Jason Deakins The antlion hole training is unusual, because it requires the player to learn a new skill in combat. This is a rare case where training occurs under duress, so Alyx states the problem and helps in the fight without giving away the solution.
dynamicss Robin Walker You fight alongside Alyx for much of Episode One, so her combat really needed to look varied and exciting. We especially wanted to get her into some convincing physical contact with her enemies. We'd always wanted to do this kind of dynamic character interaction, but getting the NPCs into position for their interactions has a wide-ranging set of problems. We ended up taking an opportunistic approach for Episode One; Instead of figuring out how to maneuver characters into proximity, the system monitors their positions, and fires the appropriate animations whenever it notices that they're correctly aligned. Given how well these interactions worked out between Alyx and zombies, headcrabs, and antlions, we're looking forward to extending this kind of behavior to all of our NPCs.
burrowblocking John Guthrie This three level parking garage is where the antlion burrow training pays off. Because we've taught the player the burrow blocking mechanic earlier in a less hectic environment, the problem here becomes not what to do with the burrows, but where to find the cars to block them while fighting off a horde of antlions. The burrows themselves went through several iterations. At first, playtesters had a hard time seeing them, and once they'd pushed a car onto one, they often weren't sure if the hole was actually sealed. We eventually solved both of these problems by adding a particle effect to the burrows. This effect makes them recognizable even at a distance, and its absence is a clear indication that a burrow is blocked.
artpassgarage Gautam Babbar We generally design and prototype the basic gameplay in a level before we apply much art to it. Throughout the first several months of playtesting this garage map, the geometry was nothing more than basic shapes and textures. After we'd finalized most of the gameplay elements, we began to flesh out the visuals for the area. For this level, we left the office and took reference pictures of various garages. From these shots, we pulled out everything we liked and that we thought we could pull off well. We combined these visual highlights into what we call a 'styleguide map', which is a standalone map with no gameplay that we use strictly as a visual reference. For this level, we actually made two styleguides - one a destroyed garage, the other intact. After the look was established, we brought the playable map's visual quality up to the level of the styleguides. Often, a map's geometry needs to be changed as the art goes in because areas that worked in the abstract version no longer make sense in a map that now looks like a real place. For instance, the side rooms where two of the cars are hidden were moved several times in order to make them feel more naturally part of a parking garage.
hdrcomment Chris Green Episode One is our first project to use HDR lighting heavily in dark, indoor environments. The interaction between the flashlight and the auto-exposure calculations done for HDR presented a real technical challenge. In dark areas where the flashlight was the only source of illumination, we found that we'd often end up with grossly over-exposed views. We ended up compensating for this by using a different set of exposure parameters when the flashlight was turned on. In particular, we drastically shrunk the region of the screen examined for exposure calculations, which permitted us to concentrate only on the much smaller area lit by the flashlight.
followthewire Gautam Babbar This area is the dramatic culmination of all the lightless combat that comes before it. We wanted to create a dynamic fight that lasted several minutes while you waited for the elevator to arrive. The first iteration of this battle was very different from what we eventually shipped. The space was larger, had water in it, and wasn't completely dark. Water is relatively expensive, performance-wise, so we cut that in favor of more zombies. We made the level smaller to ensure that the player would see the elevator and recognize the problem that needed to be solved before the fight started. We killed the lights both to enhance tension and to make this scene a final test of the dark-fighting skills that the player develops over the course of the episode. Finally, we added a wire running along the ceiling from the elevator to the powerbox to give players a guide as they familiarize themselves with the area.
alyxthekey Chet Faliszek In early versions of the episode, Alyx was much more vocal about giving the player hints. However, playtests showed it was much more satisfying for players when Alyx stated a goal and then stepped aside until that goal was accomplished. Because of that feedback, almost all of Alyx's hint lines were cut. Eventually, though, we discovered through more playtesting that although players didn't like having Alyx hand them unsolicited hints, they did want to be able to explicitly request help from her. We added some of the hint dialog back in, but it's only accessible at the player's request by plus-using Alyx. Unfortunately, we learned these hint lessons late in the development cycle and didn't have time to properly train players for this feature. We plan to integrate the hint-on-demand dialog more thoroughly in future episodes.
artgameplaystandards Ted Backman Our art and gameplay standards encourage players to build a visual dictionary that defines how they expect things to work in the Half-Life world. For instance, even though the door to the powerbox room is metal, and would probably have a metal crossbar holding it shut, we barred it with a wooden plank. Because we've been consistent throughout the game, the player should recognize that a wooden plank can be both broken and manipulated with the gravity gun, properties that wouldn't be immediately apparent about a metal bar.
zombinegrenades Adrian Finol We're really happy with the zombine's grenade behavior. It adds sudden danger spikes to the zombie horde, which force players to quickly re-prioritize their targets. And since the player can grab a grenade out of the zombine's hand with the gravity gun, these danger spikes can be converted into offensive opportunities. This kind of turnaround skill shot creates some dynamic, satisfying hero moments for the player. Originally, we didn't allow the player to snatch zombine grenades because we felt it broke the fiction of the gravity gun - if players could grab a zombine's grenade, why couldn't they grab the Combine soldiers' guns? After playtesting the grenade steal, though, fun won out over consistency.
c17vista Gautam Babbar This City 17 vista is an explicit visual reward for surviving the elevator battle. Since early playtesters told us that we weren't communicating just how damaged the city was, this sweeping view of an extremely messed up City 17 serves a practical purpose as well as being a nice moment of calm between storms. The framing of your first view of the Citadel in this vista space is very deliberate. We included various leading elements, such as wires and light poles, that all drive the player's eye to the Citadel.
kleinercast Marc Laidlaw One thing we try to do when we're integrating storytelling and gameplay, something that has become a hallmark of ours, is to include non-linear bits of narrative - things that action-oriented players don't have to sit through, but that are available to players who want to learn more about the background of the story. Kleiner's broadcasts on the public address monitors are a good example of this method. Apart from the strong visual image of Dr. Kleiner replacing his former boss on the giant screens, his speech conveys a lot of dense information about the state of the world and how things have changed due to the events of Half-Life 2. We settled on this particular location for the Kleinercast as one of the few logical places where players can watch it in peace or move on to the next encounter. It's essentially a footnote embedded in the world. Which makes this a footnote on a footnote.
metalplates Ido Magal Later in the level, there's a Combine gunner protected behind some metal plates, just like the ones blocking the player's way here. We placed them here as a training tool to remind players that the gravity gun can grab and detach these things.
silhouette Ken Birdwell Rappelling soldiers presented a difficult training problem, because we've found that it's tough to focus the player's attention upward. This entire alley was carefully designed to ensure that the player would see the descending soldiers. First, we framed the soldiers with a straight line of buildings. Then we had them run across the rooftops so that they were starkly silhouetted against the sky before they dropped down in front of lightly colored buildings. Finally, we added a distinctive sound to the rappelling action so that players would recognize it later in the game.
citylook Randy Lundeen The post-Half-Life 2 look of City 17 was difficult to nail down and went through many changes. We wanted to establish several things; Primarily that this was a different part of the same city with a slightly different atmosphere and that it had been severely damaged. This street was a test bed for a lot of our visual design work. First, we built an intact city street and then we beat up certain buildings, in some cases removing them entirely so that more destruction was visible in the distance. We did an initial lighting pass in the game engine, and then took screenshots of various locations. Using Photoshop, we manipulated those screenshots to establish a color scheme. Photoshop lets us quickly iterate through all kinds of skies, lighting styles, and color schemes. The environmental lighting colors that we ended up with were based on some photo references of the sun filtering through the smoke from a forest fire. Some falling ash effects and a closer-than-usual fog plane helped sell the effect.
crouchingalyx Robin Walker Character AI is all about putting on a good show. As we neared the end of production, we were still unhappy with the way that Alyx handled herself in combat. The most common thing she did was to run backwards while shooting at enemies. It was realistic, but boring. We added crouching and aiming at the last minute, and though it didn't change her combat effectiveness in any functional way, it made her a whole lot more fun to watch. This is a great example of how relatively minor presentation and behavior changes can have a major impact on entertainment value.
tripminetraps Ido Magal Tripmine traps are great, but they were sort of hard to justify given the total chaos of City 17. Even though we couldn't use tripmines a lot, they made sense in this interrupted ambush scene.
sealingoffcafe Ido Magal This explosion permanently seals the cafe door, which has a few benefits. From a design perspective, we've found that when we limit the amount of backtracking players can do, it gives them confidence to venture forward. From a practical standpoint, we can clean up the now unreachable entities, giving us a big reduction in overhead. It also helps to minimize potential bugs and exploits.
noammo Ido Magal Originally, the player didn't get any weapons until the end of this map, so rollermines were the only way to kill the soldiers. As we added more content to previous levels, it became impractical for players to be without a gun for so long. As a result, players get weapons much earlier now.
alyxsniper Steve Kalning One of the primary design goals of Episode One was to convey the sense that Alyx and the player are a team. This sniper sequence provides an opportunity for Alyx to offer combat support in a cool new way. It also gives the player a chance to watch zombies get sniped up close and from various angles.
skybridgezombies Ido Magal Players didn't have any weapons in the original version of this map. That made it a lot more important to remove the boards with the gravity gun so that Alyx could snipe the zombies. Once weapons were added, though, the skybridge became less of a puzzle and more of straightforward a combat event. We added more zombies to increase the challenge, but pulling the boards off is still the most fun way to get through this section.
garrisonapproach Tom Leonard Our AI is inherently unscripted, which means that we have to design spaces that permit our characters to make good choices. The AI is better able to make intelligent decisions when there are alternate routes through a combat space. This hallway started out as a straight-shot corridor with a door at the end for soldiers to enter through, but this design didn't provide the AI with enough choices to make the soldier behavior very interesting. Adding an additional space on the side allowed them to find cover and flank the player, both of which dramatically improved the entertainment value of this encounter.
doorblasts Charlie Burgin The first prototype of Episode One's door-blast effect was here in the Combine garrison. Being peppered with chunks of wood while soldiers poured into the room through a haze of smoke proved to be an effective dramatic tool. It was also an excellent way to simultaneously ungate the player and flood the area with enemies. It was so unanimously successful in playtests that we ended up adding it in several places throughout the episode.
alg_vs_apc Scott Dalton At this point in the action, we really felt that we needed a combat crescendo. Antlion guards make great boss challenges, and we decided to add some combine forces to the mix because watching AI characters fight each other is always entertaining. This setup had a few other benefits as well. Since players had previously only fought alone against the guards, this was the first time they'd actually witness second hand the effects of a Guard headbutt. They'd also see an APC in action, and, in case there was any doubt, get definite proof that Combine soldiers and antlion guards don't get along, underscoring the collapse of Combine dominance in City 17.
ALG_strategy Steve Bond Antlion guard arenas have a few specific design requirements. For instance, since the guard is only armed with a melee attack, we can't let the player reach any place that's inaccessible to the guard, such as rooftops and other high perches that the player could only arrive at after being launched by a guard headbutt. The arenas also need plenty of physics objects for the guard to toss, and at least one unlimited ammo crate so that the player can't run out of ammunition before killing the guard. For this battle, we also introduced a steady stream of regular antlions to limit the player's ability to constantly circle the antlion guard.
spacerefinement Charlie Burgin In early versions of this area, there was no side passage off the street and the gash in the road was created by the gunship that the player later fights in the hospital attic. As development progressed, however, gameplay, story, and performance requirements made this initial design unworkable. The new side passage provided a short break in the combat tension after the boss battle and also helped us to stay within our performance budget.
airventcollapse John Guthrie After the antlion guard fight, playtesters were reporting some combat fatigue. We decided to include an environmental puzzle here to break up the pacing before the subsequent street battle. We originally worried that a densely packed room full of hopper mines, tripmines, and explosive barrels was a little too implausible. But playtesters loved the sudden reveal of the room and then enjoyed navigating it, so this ended up being another case where we accepted a trade-off between fun and maintaining a strictly consistent fiction.
collapsingelevator John Guthrie At one point, this was the site of a physically simulated elevator puzzle. It was kind of neat, but it caused a lot of problems in playtests. Even though the puzzle mostly obeyed the laws of physics, it wasn't at all in line the with the way we'd trained players to expect elevators to work in our world. We considered adding some earlier training to support it, but quickly abandoned the idea in favor of a redesign that was more immediately understandable while still being fun.
foreshadowgunship Gautam Babbar Whenever possible, we like to foreshadow impending boss battles by introducing the enemy before the actual fight. In this case, you know you're going to be seeing that gunship again pretty soon.
gunshipcloseup Gautam Babbar Instead of letting the gunship AI have its own way here, we forced the ship to crash right into the attic. It's a dramatic payoff for winning the battle, and it gives players an opportunity to examine a gunship up close at their leisure.
gunshipdesign Scott Dalton We designed this gunship battle to create a dynamic evolving experience while still keeping the player within a constrained area. Initially, this space appears straightforward, and provides plenty of cover. As the environment gets progressively more damaged, combat becomes more challenging; players are increasingly open to enemy fire and the path to the rocket crate becomes more difficult to navigate. As the roof breaks apart, however, the gunship also becomes more visible and therefore easier to hit, keeping things relatively in balance. The lighting in this area was tuned to play off of the HDR tonemapping effects, between the dark inner spaces and the progressively open bright sky above.
hospitalart Randy Lundeen The hospital was a completely new interior space that we had to design pretty much from scratch. Like most of City 17's visuals, it was inspired by Eastern European architecture. The surgery lamps and the overall white and yellow color scheme were drawn from photos of a hospital in Chernobyl. The tile work and the high archways were chosen to give the area the institutional feel of an old European hospital, and the beds were based on some old World War 2 images. In fact, we avoided modern-looking fixtures and furniture altogether in order to differentiate the place from a contemporary hospital.
shotgunalyx Robin Walker We designed this area to be an entertaining showcase for NPC combat. Because of our dynamic AI, these kinds of battles never play out the same way twice. Players often like to sit back, watch the show, and then dive into the fray at their own discretion. We also felt it was time to introduce a new combat ability for Alyx, so we gave her a shotgun here. Not only are shotguns terrific for zombie hunting, their size and ponderous handling characteristics make for some great combat animations.
bangingzombies Gautam Babbar The door-banging zombies were supposed to give players a safe glimpse of a threat they'd have to face later in the level. In the original design, players couldn't open the door; The zombies would burst through on their own after the player had done a little exploring. We abandoned that plan when many playtesters exhibited a pretty much singleminded fascination with opening the door as soon as they saw it. We made the door openable, though if players ignore it the zombies will eventually break it down themselves.
hospitalprops Laura Dubuk To make the set of empty corridors look like a hospital, we chose some iconic hospital props that could be used multiple times throughout the level. Then we built the models with details, multiple skins, and vertical and horizontal elements that would be visually interesting in the space.
hospitalrespite Gautam Babbar Too much of the same type of uninterrupted gameplay causes fatigue. Through repeated playtests, we learned that by the time players reached this part of the hospital, they were ready for a break from intense combat. In response to that feedback, we inserted this relatively calm exploration puzzle as a change of pace. It gives players a respite from combat while still presenting them with an interesting challenge.
turrets Gautam Babbar This turret scenario was designed to showcase Alyx's ability to provide cover for players in combat. She always hangs back a little, blasting anything that moves. In the original version, players could knock over the lightly protected turrets with a single rocket fired from the safe end of the corridor. We thought it'd be a nice way for players to feel like they'd pulled one over on the Combine. Unfortunately, playtesters routinely thought that they'd discovered a bug or, at best, an exploit that had arisen from sloppy design. So, in this case, a situation we'd deliberately created to make players feel clever actually caused them to think we weren't doing our job very well. As a result of this feedback, we added a force field and additional grating to better protect the turrets.
nodegraph Robin Walker What you're seeing here is a visual representation of a nodegraph - a set of nodes and the connections between them. Nodegraphs tell our NPCs how they can move around the world. It's not a specific set of instructions, but rather a sort of information repository. Among other things, NPCs use the nodegraph to dynamically chart paths to distant areas, find cover, and scout out firing positions with a clear line of sight to their enemy.
zombietrap John Guthrie This space was designed to lure players onto a section of breakable floor that drops them into a room full of zombies. Players are enticed into the trap by some reward items and a chance to peek into a hole. We like to surprise players, but we never want them to feel that they've been treated unfairly.
oldschool Marc Laidlaw Barney, like Dr. Kleiner, is one of the characters with the deepest roots in Half-Life 1. His personality is more iconic, and retains more of the comic stylization of the first game. This type of character allows us to mix up the mood a little bit - to inject some absurd humor into the otherwise grim scenarios of the Half-Life universe. While characters such as Alyx and Eli Vance have allowed us to explore more realistic dramatic possibilities, we are still very much attached to our roots in satire and black humor.
barneysbigcrowbar Jake Nicholson Barney's big crowbar scene required a few tricks to pull off. There are actually three separate crowbar models in the sequence. First, there's one stuck in the machine. When Barney grabs that one, we remove it from the world and switch on a crowbar that's been in Barney's hand the entire time, only invisible. Both of these models are purely decorative, so as soon as Barney makes his tossing motion, we hide his crowbar again and create a third, useable crowbar that then bounces to the ground.
advisorsighting Matt Scott We wanted players to realize that they've been spotted and the Combine are now aware of their arrival at the train station. It sounds like a simple task, but it actually took a lot of thought to draw the player's attention to the various events that communicate this message. First, a train horn sounds, which gives Alyx an opportunity to mention that the station is in sight. Next, the lights go off to grab the player's attention and to make the monitors stand out in the dark. At this point, the player should be looking at one of the monitors, so, finally, the Kleiner transmission is interrupted briefly by a Combine advisor. Originally, the advisor appeared on a jumbotron outside, but we were never able to reliably make playtesters look at it. The flashing Combine camera should also provide some indication that trouble is brewing. Though it's not a proper gate, the zombie draped over the exit is designed to slow the player down just long enough for Alyx to finish her lines.
strollwithbarney Wade Schin Originally, Barney started off in this map in the doorway down by the citizens, but playtesters tended to wander around for a while before stumbling across him. We moved him up here to guarantee that his scene with Alyx would unfold before players began any exploration. He's standing over a dead metrocop because it's a plausible-looking long term activity, in case players don't move directly down to him. Nearby reward items also tend to draw players toward him.
escortmap Ido Magal Here we wanted to include something a little different - an escort mission. Most of our gameplay involves constant forward motion, so we wanted to design a situation where players would fight through the same basic area multiple times. This temporary backtracking would create a series of encounters where players had a full tactical awareness of their surroundings. Once again, all of this turned out to be more easily said than done, and this sequence went through a lot of iterations. Originally, the train yard was one big space. This approach had a couple of problems. Since players had a constant, unbroken view of the entire area, it was virtually impossible to maneuver enemies into position for staged combat events. And because they could always see the goal, players didn't get much of a sense that they were leading citizens somewhere the citizens couldn't get to on their own. Ultimately, we broke the environment into two different spaces, a parking lot and a maintenance building. Because neither area can be seen from the other, we're able to repopulate the spaces with new, more deadly combinations of enemies while the player isn't looking. It also makes the journey feel lengthier and more significant.
plausiblerepopulation Ido Magal We wrestled with the problem of plausibly repopulating this area with soldiers between each trip. After several iterations, we decided to have the soldiers jump in through some high windows. This solution has several advantages beyond maintaining a credible fiction. It makes the incoming enemies more immediately visible and, since the windows are unreachable from the ground, players aren't able to exit through them. Plus, leaping soldiers turn into tumbling ragdolls when shot, which is always entertaining.
newtrainstation Randy Lundeen We needed a train station, but we didn't want something that was too similar to the one in Half-Life 2. We decided to give this station a more industrial look, to make it a place where trains were repaired and freight was offloaded. We included some Combine elements to help explain why the strider can't fire through the various strategic barricades required by the game design.
separatefromalyx Ido Magal We separate Alyx from the player here to make the strider battle a more intimate combat experience. While we generally want Alyx to be useful to the player, bosses tend to require a specific combat style to beat, and we've found that it usually doesn't make gameplay sense to keep her around. Plus, boss battles are the player's big hero moments, and having too much help dilutes the sense of individual accomplishment. Alyx more or less sits out all of our boss encounters.
newstrider Steve Bond For this climactic battle, we created a new AI that makes the strider a more interesting opponent. It has a snappier cannon attack, can better track the player's movements, and it now has the ability to target the environment in dangerous ways. For instance, its cannon fire can shove heavy shipping containers straight into the player.
padlockmistakes Erik Johnson This shipping container used to be accessible only after the player destroyed a padlock. Given the amount of stress during this part of the game, even a simple puzzle (in this case, destroying a lock) would be completely missed by the player. In the end, we felt like the arena we had built for the player to fight the strider was fun enough without this added element, so we removed it.
crumbtrail Jeff Hameluck We often use goodies - such as this crate and the scanner battery around the corner - to guide players along a preset route. We want players to hit their marks during a battle without drawing attention to the fact that they're being subtly manipulated down a particular path.
tempcover Chet Faliszek We wanted to keep the tension high in this fight, but we also realized that players would need some cover. These destructible panels satisfied both of those design goals. Effectively, they're timed shelters. Players can hide behind the panels, but the strider will target them until they're destroyed. This gives players brief periods of safety during which they can plan their next move.
battleofreflexes Steve Bond We noticed during playtesting that players were often too afraid of the strider's weapons to stand in front of it and fire rockets. This was kind of a problem because rockets are virtually the only way to kill a strider. To help players, we modified the strider's AI so that a player-launched rocket will significantly delay the strider's attack. This 'battle of reflexes' lets players guide their missiles in safety, as long as they get their shot off before the strider does.
youremynewhero Doug Wood Along with vistas, positive feedback from Alyx is one of our primary means of rewarding players. In this case, Alyx's excitement over the strider's destruction adds a sense of closure to the battle and gives players the satisfaction that someone witnessed and appreciated their heroics.
traincarmodel Laura Dubuk The train the player rides out of City 17 had two major design goals. It had to visually connect the end of Episode One to the beginning of Episode Two, and it also needed to address some functional gameplay requirements of the second episode. Using reference material we'd collected on European train cars from the 1980's, we built a basic version of the train that level designers could test. Once we got the thumbs-up from them, we added textures and lots of little details. The result is basically a caboose combined with rounder, more streamlined elements from a passenger car.
finalereqs Lars Jensvold Apart from being a big visual payoff to the episode, there were several story requirements that this ending sequence needed to convey. It had to make it very clear that the Citadel was destroyed, that the Citadel pods had escaped, and it needed to imply that a data transmission beam was streaming out of the ruins. We discovered that Alyx had to be mostly silent during this scene or else players tended to look at her instead of all of the chaos around them.

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