The Stack

Tempest had a knob. Rotary controllers of this sort weren’t uncommon in videogames of the day — why, the very first videogame to hit it big, Pong, used a pair of knobs. But they’re not common on today’s home computers or gaming consoles. (As far as I know, the last console to provide knobs as a standard feature was the Atari 2600.) I suppose the steering wheel controllers sometimes used for driving games are effectively a knob variant, but that seems cumbersome for the purpose. (If you’ve actually tried using a steering wheel to control a non-driving game, I’m curious about how well it worked.)

The usual way to compensate for this on a PC is to substitute the mouse, which works pretty well — like the knob, it’s effectively an analog device, allowing quick and precise movement by mapping motion on the screen directly to motion of the controller. It doesn’t work quite as well as for Tempest as it does for Pong and its ilk, though. Pong maps the rotary motion of the controller to linear motion on the screen, so switching to a controller that uses linear motion actually makes the mapping a little simpler and more direct. Tempest, on the other hand, has genuinely rotary motion on screen. Any mouse-based control scheme is going to wind up either (a) moving the player in the opposite direction from the mouse motion some of the time, or (b) being more complicated than the simple two-direction spinning of the original.

Now, Tempest 2000 has the additional handicap of having been developed primarily for the Atari Jaguar, a machine that had no knobs, no mouse, not even an analog joystick. It was built with a digital D-pad in mind, and the port supports nothing better. I might as well use the keyboard; switching directions is slightly faster that way. It’s probably not as bad as it sounds, though. The art of using digital controls to simulate analog ones is well-developed by now, and probably familiar to most gamers, if only subliminally. But it does suffer the inversion problem already noted about mouse controls. Pressing left moves you clockwise and right moves you counterclockwise, even when you’re at the top of the tube, where clockwise is right and counterclockwise is left. One gets used to this, but it’s easy to get momentarily confused, and every moment of confusion is a potential death.

Not every level in the game actually involves a closed curve — about half of them have endpoints, and are equivalent to lines. They’re lines bent into various shapes (one of the early ones is in a V shape that always makes me think of the Videlectrix logo), but motion on these levels is essentially linear rather than rotary. Does this make it easier? Not always! Context and perspective are important here. Some of these levels put the line above the middle of the screen, so that the monsters are below you — think of the normal tube-like view, but with the bottom half of the tube cut off. Or rather, don’t, because if you do, you’ll expect the controls to be inverted, like they are on the top half of a full tube. They’re not: left means left and right means right, just like you’d expect. The fact that I find these levels so confusing shows something about how quickly intuitive expectations can be changed.

I had intended to get back into Etherlords his weekend, but I just didn’t feel like it. Sometimes the brain wants a rest. And so I choose a game that the spinal cord can play by itself. Tempest is of course the original fast-paced shoot-em-up-in-a-tube, and Tempest 2000 is its by-now-also-retro remake with a toe-tapping techno soundtrack (played directly off the CD, olde-style).

There was a brief but substantial wave of these remakes of “classic” arcade games around the turn of the millennium: re-imaginings that took advantage of 3D hardware and new innovations in game design, or, to put it another way, attempts on the part of the new IP holders to cash in on nostalgia by bolting on texture-mapping and power-ups and rudimentary storylines. Tempest 2000 wasn’t really part of this trend, having come a few years too early — despite the name, it was originally released on the Atari Jaguar in 1994, and its PC port in 1996. Because of this, it doesn’t quite fit the template. It has the powerups, sure, but it thankfully avoids spoiling the abstract purity of the original with a storyline. And (outside of the bonus levels) it doesn’t have texture-mapping — it uses Tron-esque solid-filled polygons instead of the bare wireframe of the original, but that’s as far as it goes.

Instead, the graphics technology it wants to show off is particle effects — there’s a constant spray of rainbow confetti in the background, and there’s often enough explosion debris and floating word residue on the screen that it’s hard to see what you’re doing. Seriously, check out the screenshot. The thumbnail doesn’t do it justice. It all reminds me of the complaints about Space Giraffe, a game which I’ve never played and don’t know much else about. Well, as you may already know, but I did not, Space Giraffe is in fact a remake of Tempest 2000 by the same designer. I’ve been vaguely aware of Jeff Minter since Llamatron, but somehow didn’t notice that he was involved with this game, probably because it doesn’t have some kind of quadruped in its title.

Filtering out the visual noise is of course a skill that you can learn. Some have gone so far as to call it the fundamental videogame skill. And this is very much a skill-based game. The day’s practice has seen me make substantial improvement already — I can now consistently clear level 20 (out of 100) from a standing start — but it’s not because I’ve made discoveries or varied my tactics or anything like that. I’ve been hesitant to start games of this sort since starting this blog, because they provide no guarantee that I’ll ever be able to complete them. With an RPG, there’s always the option of level-grinding until it’s easy. With a FPS, you can generally get through the hard bits by saving more often. With an adventure, there’s always walkthroughs, or, failing that, reverse-engineering the data files. But if a level in a twitch game is beyond you, there’s not much you can do. Tempest 2000 effectively provides infinite continues — within a session, you can always start a new game at or near the level you died. I expect I’ll be needing that.

Spoilers strut about boldly in the daylight ahead.

It turned out that I had only one major set-piece battle to go before the end of the episode, against a tripod in an enclosed area full of boxcars and other obstacles. The tripod is too large to follow you as you wend your way through the maze-like environs, but its weapons are strong enough to physically alter the environment in ways that must have taken a good deal of careful planning on the part of the designers.

After that, Gordon and Alyx set a train in motion, hop into the caboose, and watch the city explode noiselessly in the distance. At least, it’s in the distance at first, as you see the ships flying out of the towering citadel just in time to escape and speeding off in all directions. Then the fireball (plasmaball? otherworldly-dimensional-energyball?) engulfs the places your train has just sped through — it’s sort of a “Yee-haw!” moment, staying just ahead of the wall of white in your wake, until you have the dismaying realization that you’re not going to make it.

I’ve had nightmares like this. Dreams of near-escape, followed the realization that you’re doomed and powerless to do anything about it. The sense of doom can be surprisingly peaceful at these moments, because if there’s nothing you can do, there’s no need to react in any way. Being on a train isn’t completely necessary to the feeling, but it adds a lot to the sense that your course is beyond your control. And that’s Gordon’s life in a nutshell, isn’t it? Trains have been a major part of Half-Life all along, bringing Gordon to places he doesn’t want to be, literally railroading him.

Speaking of hardware modification, it turns out that I was right: all that I needed to pass the Point of Certain Crash in Half-Life 2 Episode 1 was a second gigabyte of RAM, which seems to cost about two cents per meg these days. So the stated “minimum requirements” of the game, which would have it running on a fraction of the RAM I had beforehand, are a lie. This is probably pretty common. There’s little motivation for game producers to tell people in advance that they shouldn’t bother buying their games.

I’ve mentioned before how the structure of Half-Life 2 makes me end most sessions in the middle of a difficult battle. The latest quit-for-the-night scene for me is one of those scenes where people start following Gordon around and get massacred for their trust in my ability to defend them. This time around, though, it’s not just a regrettable happenstance. Defending them is in fact my explicit goal: Barney has dragooned me into shuttling people from a safehouse to a waiting train, four at a time. (This seems to be a magic number for the game engine. Whenever NPCs are spawned dynamically, there are always four of them. New folks show up only as fast as you let the old ones die. If it were a movie, I’d suspect that they only had enough money to hire four extras.)

So, it’s an escort mission, that traditional bane of shooters. I don’t know yet if getting my charges killed actually makes any difference in the game here, and on the basis of precedent, I suspect it doesn’t. But for various reasons, I’m unwilling to let them die, and this makes the scene harder than it would be otherwise. The fact that it is my explicit goal is of course part of it. There’s also the fact that it’s my fault that they need to get on the train in the first place — the reason they’re fleeing the city is that it’s about to blow up, due to my own actions in the endgame of Half-Life 2.

But also, it just seems like discharging a karmic debt. The whole episode so far has essentially been one long escort mission — one viewed from the opposite side. Gordon frequently has to concentrate on things other than shooting, like operating machinery or pushing cars onto antlion burrows to block them. And whenever the player is occupied in this manner, Alyx covers him. There have been battles where I’ve hardly fired a shot. In one of the scenes shortly before where I am now, Alyx climbed up onto a high vantage point with a sniper rifle to pick off enemies while I ran ahead. I’ve played that exact scenario in several other games, but always as the sniper. So after being the beneficiary of so much uncomplaining protection, it would be ungracious to refuse the same to others.

Obtaining the last piece of the Five-Fingered Fist of God (as I like to think of it) opens up a passage to the alien spacecraft that started the whole mess. Not that I’d have guessed that is was an alien spacecraft without the level’s name in the automap screen. The decor is less technological-looking than a lot of the areas that are supposed to be castles and chapels and the like, consisting mainly of busy green textures that look like jade inlays or something. (I can accept that alien technology looks different from ours, but this alien is supposed to be the source of all the advanced technology we’ve seen in the game.)

This section made me very apprehensive. Not because of the darkness, or the whispery voices that get louder as you progress, but because of its generosity. The very first room in the alien ship is a smorgasbord of ammo and healing items, the sort of thing that says “You’re going to need this.” In a game where rooms like this occur frequently, like Serious Sam, this wouldn’t mean much. But here, the game had been very stingy with me for a long time, so the sudden change of heart seemed to signal something very bad to come.

This was followed by a cavernous room packed with monsters, including an Inquisitor and multiple Crusaders. At any prior point in the game, this would have been very difficult, as I’d be dodging missiles from multiple directions. As it was, I more or less stood at the entrance and let the Five-Fingered Fist of God clear out most of the room. It wasn’t quite as thorough as Doom‘s BFG would have been, so I did in fact have to use a little of my freshly-snagged ammo for mopping up, but I still hoarded most of it. After that came a couple more supply caches, including one so full of Energy Cells and Full Healths that I had to leave most of them behind.

(Energy cells are the ammo for the Mauler, the second most powerful weapon in the game. It’s kind of like the standard FPS shotgun (otherwise absent here) in that it has a slow rate of fire and does damage in a scatter pattern, but it’s a scatter of disintegration beams that are still pretty effective at a long distance. Looking it up just now to find its name, I discovered that it has an alternate fire mode that I didn’t know about and never used, a “torpedo mode” that fires an energy ball that breaks into more energy balls on impact. Maybe that would have helped in that stretch where I had so much trouble. It sounds like a real room-clearer.)

After the Energy Cell cache was a new level called “Entity’s Lair”, which the automap claimed had no monsters at all. Furthermore, just walking around opened another cache containing more Energy Cells. My apprehension increased. What on earth was going on?

Well, it turned out that this was in fact the level with the final boss. (When it made its appearance, the map mode updated the monster count to 1.) And it was kind of anticlimactic — definitely not the hardest fight in the game, not with the Fist of God at my side. Maybe the point behind all that Mauler ammo was to trick you into using it instead. I didn’t even try. After spending so much time hunting for pieces of the Sigil, it seemed like a waste to not use it.

The game doesn’t waste much time on what happens after you’re done fighting. There are multiple possible endings, but in the one I got, there’s a perfunctory illustrated slideshow cutscene in which it’s asserted that everything is hunky-dory now, and then Blackbird emerges from the woodwork with a come-hither glance, intending to (in her words) “reward you… personally” for some reason. And that’s that! Look at any writeup of Doom-style games, and you’ll find Strife praised for its rich, deep plot. And, well, it has a plot. The mere fact that it’s there is enough to make it seem deep and rich in comparison to other Doom-likes.

So, looking back on the experience, I have to ask: apart from some amusement and sating my sense of completism, did I get anything out of this game? Does it have anything to teach us? Obviously it did when it was new: it introduced Doom fans to the concept of NPCs, and experimented with combining FPS and RPG elements. And as fond as I am of saying “Ultima Underworld did it first”, I have to admit that Strife chose a fresh approach to that combination, one that emphasizes the FPS part and makes the RPG aspect subordinate to it. ¹I say “chose”, but this may or may not have been the authors’ intention. The emphasis may have been a result of the engine.

There’s also at least one original, and still-underutilized, pure-FPS idea in here too: use of the ceiling. People don’t normally look at ceilings, so things up there can be hard to spot. (Especially in places where the ceilings are high, because the graphics engine used here only lets you raise the view so far.) So Strife gives you ceiling-mounted automated gun turrets — stationary turrets themselves being something of a new wrinkle at the time — and it gives you Stalkers, small spider-bots that crawl on the ceilings and drop down behind you to attack. Stalkers make a distinctive ticking noise as they creep along, and whenever I heard it, I knew I was probably also going to hear the plunk that meant I should sprint forward a few yards and then quickly turn around.

On the side of negative lessons, the one place where I felt that Strife really fell down was that it wasn’t clear enough in the beginning about how things work. Which is a very unusual problem for a FPS, but there it is. The person who gives you your first mission warns you not to “set off every alarm in town”, so when you set off an unavoidable alarm in the course of that mission, it’s easy to feel like you’ve made a mistake and waste some time looking for a way around it. At the same time, there’s another person not far away who offers you a similar mission, but he’s a liar and fraud, and secretly in league with the Order: doing as he says does in fact set off every alarm in town, which can disastrous if you chose to do his mission first. Something like that might have been okay later in the game — arguably the business with Macil is similar — but when you’re still struggling with the basics, like where you are and who the Front is and whether you should be accepting missions from strangers at all, it just adds to the confusion.

For that matter, the game itself never addresses the questions of your immediate situation. The moment you select “New Game”, you’re in a room in a sewage treatment plant, armed with only a knife and being attacked by an Acolyte, with no clue of why. The in-game intro tells you about the history of the Order, but nothing about your personal history — even the detail that you’re a “wandering mercenary” is only mentioned in the manual. This strikes me as exactly backward. The important thing for the intro to do is establish your place in this world, to orient you. The details of the environment can be revealed over the course of the game, or relegated to the docs. I think of Half-Life 2 and Quake 2, where the opening cutscene is all about showing how the player character arrives in the gameworld.

Anyway, I’m glad I played it, but I don’t think I’ll be trying for the other endings. (The cutscenes can all be found on Youtube anyway.) For next time, I’m going to try to wrap up some other stuff that I’ve started but not finished on this blog.

Between Strife and Etherlords and Half-Life 2, I’ve been seeing a lot of cyborgs lately. Like zombies, they seem to be one of the stock videogame bad guys. I suppose this means that a lot of people find them emotionally resonant or something, evoking alienation from one’s body, enhanced by fear of mortality in the case of zombies, and of technology overpowering humanity in the case of cyborgs. Both, in different ways, represent anxieties about the future.

Although I understand these fears well enough to name them, I’ve never really felt them, and often find zombies in games more irritating than frightening. I suspect this is because I haven’t watched the right movies. (Imagine playing Jedi Knight without having seen any of the Star Wars films.) But I get that zombies are convenient low-level enemies, with a built-in rationale for being stupid and slow-moving, and you can shoot them without qualms because they’re incapable of reason and not really human. Cyborgs have the same basic advantages, but with the additional virtue that the basic idea allows for more variation. A ten-foot-tall zombie, or one with a scorpion’s tail, would be an anomaly requiring explanation.

I didn’t intend at first to talk about zombies in this post, because I’m supposed to be posting about Strife, and there aren’t any zombies in Strife. But cyborgs and zombies are really variations on the same theme, and the distinction between the two has blurred somewhat since things like Resident Evil started giving us zombies with technological origins. If the people in that game had been transformed into monsters by nanomachines instead of a virus, which would they be? Doom put it concisely when it refused to hang its low-level grunts on either peg, calling them just “former humans” in the manual.

There’s one thing about the cyborgs in Strife that really reminded me of zombies, though, and that’s because it reminded me of a phenomenon I’ve mainly seen in survival-horror games. There’s always a moment near the beginning of those games where the characters have their first encounter with a monster and someone says something like “My god… what is that thing?” To which the player naturally responds “IT IS A ZOMBIE, DUH.” ¹Notable exception: when I played Silent Hill 2 (the first of the Silent Hill games I played), my reaction was more like “…I honestly have no idea.” Sometimes I think the designers must be doing this on purpose, trying to engage the player in a Rocky Horror-like call-and-response. Well, when you reach the inner sanctum of the Conversion Chapel and see captive humans being fed into a cybernizing machine on a conveyor belt, Blackbird ²Your contact in the Front, who comminucates with you by radio and apparently sees everything you see. She functions as a combination quest dispenser and wisecracking sidekick, and provides the closest thing this game has to a PC voice. At first I wondered if hearing Blackbird’s disembodied voice wherever you go was supposed to parallel the “voices” heard by the founders of the Order, but it doesn’t look intentional. Those voices aren’t really part of the game content, and may well have been thought up only when they needed some backstory to fill out the opening spiel. is shocked — shocked! — at what she sees, as if we hadn’t gone in there specifically looking for it . Maybe it’s just the intonation that makes me interpret it this way, but this is the game’s “duh” moment.

I’m making good progress in Strife, and confidently expect to polish it off this weekend. I have all but one piece of the Sigil, and my two upgradable stats are both one tick shy of maximum. I’m assuming that these things will change together — that obtaining the last Sigil piece will trigger one final upgrade opportunity before the end boss.

It’s getting difficult at this point, which actually surprises me somewhat. These older Doom-like games generally plateau in difficulty before they’re far advanced, apart from the occasional spike produced by bosses. You get stronger foes at more or less the same rate as you get stronger weapons. Past a certain point, things don’t get more complicated, and as long as you follow standard procedure, taking things room by room and not leaving anything alive behind you, you’ll come out okay. Later games had to come up with ways of keeping standard procedure from working — last year, I blogged about Serious Sam‘s gimmicks toward that end — but Strife didn’t. I talked about rising intensity of action in my last post, but that doesn’t necessarily correspond to rising difficulty: an abundance of loose ammo and healing items can make a pitched battle easy, and a lack of them can turn a sequence of minor skirmishes into death by a thousand cuts.

And that is in fact what’s happening to me. I’m using ammo faster than I’m finding more. This would be a good time to use the Sigil, which depletes health instead of ammo, if it weren’t for the fact that I’m low on healing items too. I had grown used to buying much of my equipment with found cash, but I haven’t seen any at all in the last few levels. Perhaps I should have hoarded it better. The Front’s home base is always willing to supply a certain amount of healing and ammo free of charge, but only if you’re below a certain threshhold, and they won’t bring you to full health, and it’s only machine gun ammo.

I should probably blame the Inquisitors. ¹Yes, there’s a religious theme in the naming of the cyborgs. I’ve already mentioned the Acolytes, and there are Cusaders and Templars as well. Even the factory where they’re made is called the Conversion Chapel. Inquisitors are the strongest monster that isn’t a boss: large bipedal armored things, armed with missiles and capable of limited flight. They probably have a human brain somewhere inside them, given what we know of the Order’s modus operandi. I’ve only met a few of them, and only in the latest chapter. In one case, it’s possible that I was actually supposed to flee it rather than engage it: right behind it was a tunnel that it couldn’t fit through, but which I could reach unharmed if I sprinted. I engaged it anyway, from the relative safety of the tunnel — standard procedure, remember? Don’t leave anything alive behind you. This choice definitely helped later, when I had to cross that room again, but that convenience might not have been worth the immediate cost. It left me depleted and scrambling for ammo, and I’ve been scrambling ever since. I’m really hoping there’s a payday at the end of this chapter.

There’s a pattern you can see in a lot of games of a sort of repeated crescendo of rising action. Each chapter builds up to a boss fight, and when it’s over, a relatively subdued segment allows you to catch your breath. So it is in Strife.

The chapters in this case don’t correspond directly to levels. Rather, a new chapter introduces a new hub area, where you can shop for equipment and wander unmolested as long as you don’t shoot anything. Somewhere off the hub is a boss fight that is your objective for the chapter, but it’s inaccessible until you complete a sub-goal or two in other areas, some of which are what I’ve been thinking of as stealth missions.

Please understand that I use the word “stealth” here in a very broad sense. This isn’t Thief we’re talking about here. I mean missions in which the regular guards (or Acolytes of the Order, as they’re called) won’t attack you on sight, but which contain either alarmed areas, or creatures that will attack you, prompting you to attack back and trigger an alarm by shooting. Triggering an alarm eventually is inevitable, but you can try to put it off for as long as possible, and lessen the alarm’s effect by killing Acolytes in advance: the crossbow, when loaded with poison bolts, kills them instantly, and is the one weapon that doesn’t raise an alarm. (It’s completely ineffective on anything mechanical, of course, which includes pretty much everything other than Acolytes and innocent bystanders.) When you’re firing the crossbow through a window into an alarmed area that you’re going to go through later, this can feel very much like a stealth game. On the other hand, when you walk right up to a guard and shoot him point-blank in full view of a bunch of other guards who just stand there and watch, it just feels like you’re taking unfair advantage of a gameplay mechanic that wasn’t thought out very well.

After stealth mode comes Doom mode. The monsters become tougher and/or more numerous, especially as you near the boss, and you bring out your heavier weapons. The idea here is, I suppose, to soften you up — to make sure that you don’t enter into the boss fight in peak condition. Strangely, this is probably helps the player overall, because it means that the boss is calibrated to provide a challenge for a hurt player with depleted ammo, and thus skillful play beforehand can put you ahead of the curve. I’m comparing this in my mind to the endless boss fights in Serious Sam, which were generally preceded by a roomful of supplies and even spawned more supplies during the fight, just to extend the experience.

Since the binding goal of the game is to collect the five pieces of the Sigil, you’d probably think that each piece comes at the end of a chapter of the sort I’ve just described. And that’s more or less the case, except for two, which are pretty much outside the chapter structure. After you obtain the first piece, Macil sends you to find an Oracle who will help you get the rest. The Oracle tells you how to get one more piece, then tells you that Macil has the next piece and that you should kill him. This is a major branch in the plot: you can choose to trust the Oracle, or you can choose to trust Macil. In fact, they both have pieces of the Sigil, but killing them both immediately seems to break the plot. At any rate, they’re both located in places you’ve already been to by that point, so there’s no ramping up of the action just to reach them.

Macil’s death was something of a disappointment. When you kill him, he emits a Spectre, a cloud-like entity that can only be hurt by the Sigil, and the entire resistance movement immediately realizes the truth: Macil was an agent of the Order all along, and was betraying them. This is an unnecessary development, unless you want your morally-tricky world, with its lesser-of-two-evils allies, to resolve into simple black-and-white. Which is what happens. With Macil’s corrupting influence purged, his second-in-command takes control of the Front, and suddenly they’re just good guys. I suppose I shouldn’t have expected otherwise.

Monsters in Doom generally start the game in a dormant state. Only when you make them aware of your presence — by walking where they can see you, or firing a weapon where they can hear you — do they start moving around and attacking. The saved games apparently don’t record information about which monsters are dormant and which are active. When you reload a saved game, all monsters reset to dormant. It’s sometimes possible to exploit this to make the game easier, but this is obviously cheap.

Now, for all I know, Strife may not share this bug. Or perhaps it did originally, but not when played under ZDoom. But maybe it does. I haven’t been exploiting it deliberately, but there’s a section where I might have triggered it accidentally. I’m just not sure.

It’s harder to tell in Strife because the rules are more complicated. If I sneak into a high-security area wearing an enemy uniform, I can generally walk past the guards unnoticed. Eventually, I encounter something that isn’t fooled by the disguise. If I fight it, save the game, die, restore, and walk past the same guards again, I don’t know for sure if they’re still docile due to the bug or if it’s just because they never got woken up.

[Update: Looks like a lot of what I say in this post is false. See the comments.]

Strife is the only game on my stack that uses the Doom engine, so let’s talk a little about what that means.

Back in 1994, I spent a few months working for one of Id Software’s competitors, Looking Glass Technologies, working on their texture-mapping routines. Given the coordinates of a polygon and their corresponding positions in a texture image, we had to render the the texture onto the polygon in perspective as fast as possible. These days, this sort of operation would be handled in hardware and abstracted through a library like Direct3D or OpenGL, but we didn’t have those things. Instead, we wrote highly-optimized code to loop over the polygon, scanline by scanline, find the appropriate point in the texture, and copy the pixel color over.

Overdraw was our nemesis: each polygon was expensive enough to render that it was a big waste whenever we rendered a polygon that was covered up by something else. Even when a polygon was only partly covered-up, it was worthwhile to try to figure out how much of it was visible and only render that part.

Sometime in the middle of all this, Doom was released. It was clear that it didn’t have all the capabilities of our library — we were rendering polygons in perspective at arbitrary angles, while Doom seemed to be only capable of horizontal and vertical surfaces, and could only rotate the camera about a vertical axis (no tilting up or down). But it was really fast. Faster, in fact, than could be entirely explained by the simplification made possible by using only horizontal and vertical surfaces. Add to this the complication that they were using highly irregular map layouts: instead of using a grid of map tiles, like Wolfenstein 3D or Ultima Underworld or System Shock, the map was a collection of walls of arbitrary length at arbitrary angles, which more or less defeats the means we had been using to eliminate overdraw.

By now, the secrets are well known. They had in fact managed to completely eliminate overdraw through a single stroke of genius: they didn’t render polygons at all. They rendered the entire scene at once, in vertical scanlines. For each horizontal position, the engine goes pixel by pixel, rendering ceiling until it hits wall, then rendering wall until it hits floor. I’m glossing over a lot of details, but that’s the essence of the Doom engine right there.

This has a couple of consequences. For one thing, it’s basically impossible for a Doom-engine game to take advantage of modern 3D hardware, because modern 3D hardware is all about rendering polygons. I can imagine someone making a Direct3D version of System Shock by taking the source code and remapping all the graphics functions to Direct3D equivalents. It might not be a perfect fit, but I imagine it would be doable with a little massaging. But there’s basically nothing in the Doom engine that even vaguely resembles a Direct3D call.

Second, the fact that the view was always horizontal in Doom wasn’t just a matter of the programmers not bothering to implement it, as with jumping and crouching. It is in principle impossible for the Doom engine to tilt the camera, because that would ruin the vertical scanlines — suddenly you’d have them intersecing the edges of walls and so forth.

And yet, Strife allows the player to look up and down. It manages this by cheating: instead of tilting the camera up, all it really does is render a higher-up slice of the same horizontal view. This isn’t quite the same thing as moving the camera upward. Rather, it’s an unnaturally distorted view, more like what you’d get by taking a photograph with the camera tilted and then looking at the photograph at an oblique angle, or something like that. (I’ll try to find or make some illustrations explaining this better.)

It’s easy to interpret this distortion as mere perspective, though, unless you’re really close to something, which makes it more noticable.