Troy GilbertGamedev 2.0

Let’s start our deconstruction with the most basic feature of the player’s character, Link: his movement. Link’s movement displays a surprising amount of subtlety. If you play The Legend of Zelda for a while, you’ll notice that Link doesn’t ever get hung up on obstacles due to unexpected collisions, nor do you ever just miss a bad guy by a pixel or two when attacking him. Yet at the same time, you’ll notice that Link moves fluidly through the gameworld; even tough the environment is tile-based, you can tap the directional pad and link will move a single pixel in that direction. If you’re moving to the left and decide to go up, down or right, Link instantly moves in that other direction when you change directions on the gamepad.

What’s happening here is a very neat trick. While Link can move a single pixel at a time, in any direction, the longer he continously moves in any direction the more he gravitates toward aligning himself with the underlying grid of the screen. The tile grid for LoZ is 16 tiles wide by 14 tiles high (including 3 tiles for the status display at the top of the screen). Each tile is 16×16 pixels. Link operates on a half-tile grid, though (32×28 tiles, 8×8 pixels each). As Link moves, if he’s not currently aligned with the half-tile grid, he is adjusted, one pixel at a time, toward the closest correction. As a result, if Link is 4 pixels off alignment he’ll line back up with the grid after moving 4 pixels.

In case that description doesn’t make sense, here’s an exercise to help demosntrate the technique:

Assume Link is basically in the center of the screen, lined-up with a tile. In other words, Link occupies a whole tile, just as he would in a strictly tile-based game (like a traditional boardgame or wargame). If you tap on the directional pad to the left, Link will move one pixel to the left. If you tap again, he’ll move another pixel to the left. This is pixel-fine control, which makes Link’s movement feel fluid.

Now, if you hold the directional pad to the left, Link will move continously. As soon as you let up, he stops. If you hold left then immediately reverse to hold right, he instantly changes direction (as he does for up and down as well). This is basically lag-free, which makes Link’s movement feel responsive.

Okay, return back to Link sitting squarely on a tile. If you tap left twice he’ll be two pixels over the left edge of his starting tile. Now press up four times. You’ll notice that after each press Link will move up one pixel. But, he’ll also move to the right one pixel, either the first two times you pressed up or the first and third times you pressed up (I don’t have the game in front of me and I can’t remember the rate at which it corrects). So, even though you never press right on the gamepad, Link has now returned to the same horizontal position as he was when he started (before you moved him left two pixels). This is the built-in correction.

What does this correction do for you?

The correction prevents the subtle but annoying problem wherein the player would “snag” on the corners of objects that he anticipated passing by. The more the player moves contiously the more aligned Link becomes, which has the same effect as speed-sensitive steering in a car.

The correction also has benefits for attacking as well. When Link attacks (with his sword, for example), the “kill zone” lies in the tile(s) immediately along his facing direction. Since enemies align along a similar half-grid as Link, the correction serves to line up Link with his enemies (as opposed to missing the enemy by a few frustrating pixels).

Observant readers will observe (as they are known to do) that this “feature” doesn’t appear in the SNES sequel, The Legend of Zelda: A Link to the Past . Even though the gameworld is still tile-based, player (and enemy/NPC) movement is not strictly aligned on any grid. We get the same corrections though, but using different mechanisms.

Movement is corrected by “rounding” the corners of most things Link can collide with. Thus, when he encounters them the “physics” of the game deflects him at a 45-degree angle along his direction of movement (e.g., if he was moving north/up and encountered a corner he would move northwest/east until he passed the corner).

Attacking is corrected in a similarly interesting way. Instead of Link’s sword having a killzone along a straight line down his facing direction, his sword “swipes” in a large arc, an arc that happens to be pretty close to full two “tiles” in the gameworld (one directly in front and half above and half below). This allows the player to attack while slightly mis-aligned with an enemy and still land a blow.

The result for both actions in both games is the same: the player’s desire is successfully expressed in the gameworld, regardless of the potentially pedantic ways of the computer.

It’s no secret that the Legend of Zelda (NES) was a watershed game. The game still has an open-world feel that titles to this day fall on their face trying to emulate, even in this post-GTA design world. This was the first game I ever played that truly was open in the sense that I could go anywhere in the game and basically approach (or avoid) any obstacle as I saw fit. The game also fits the bill as the prototypical example of an action-adventure video game, and the series (with a few minor exceptions) has continued that tradition since.

What is there to learn from a game that originally released in 1986? Twenty years later, there are still design subtleties in LoZ that are overlooked. The game is a perfect example of simple mechanics played out on a vast and varied playing field. From a complexity perspective, the game represents something achievable by any single individual given today’s technology and tools, yet we have the efforts of huge teams with comparitively bottomless budgets failing to capture the subtle qualities that simply make this game work.

In what I hope to be an insightful series of essays, I’ll be deconstructing the elements that I feel make LoZ a relative Citizen Kane of the genre, and see how those successes can translate to useful lessons in today’s games.

As a bit of a preface, let’s look at the game’s premise and detail the overall mechanics of LoZ. The premise follows the classic Hero’s Journey, with Link (the player-controlled character, who was so-named because Miyamoto saw him as the player’s “link” into the game world) out to save Princess Zelda from the evil clutches of Ganon. To achieve this goal, Link must acquire the objects of mythical power (the tri-force) and the one weapon that can kill the ultimate evil (the master sword). To this end, Link travels to many different locales (deserts, forests, mountains, dungeons), doing battle with many monsters and finding many unique weapons.

The mechanics are straightforward. Link is represented onscreen in an top-down view. The player has direct control over Link: the directions on the gamepad (left, right, up, down) correspond to movement onscreen (west, east, north, south, respectively). The A & B buttons are mapped to various actions, usually one of which is mapped to Link’s sword while the other is mapped to a special weapon or inventory item. There’s no jumping. To pick-up an item, Link simply collides with it.

The gameworld is divided into two sections: the Overworld and the Underworld. The Overworld is composed of mountains, trees, bushes, rivers, lakes, rocks, etc., what you’d expect from a classic outdoor adventure landscape. The Underworld is represented by dungeons whose entrances are hidden throughout the Overworld. Each dungeon (of which there are 9) is self-contained with one entrance/exit, each one containing a boss monster and usually an item of significance near their end. The dungeons don’t have to be visited in any particular order, but some of them have accessibility barriers that require attaining items of significance from other dungeons in order to be successful. The final dungeon is home to Ganon, whose defeat is the final goal of the game.

The gameworld is viewed one screenful-at-a-time. When Link hits the edge of the screen (or a doorway on the edge of the screen when in the dungeons) the game “pauses” momentarily while the view shifts/slides to the new screen, at which point player-control resumes. Each “screen” is usually transient, with enemies regenerating and other elements “resetting” when a player exits then returns to a screen. Enemies cannot pursue Link out of one screen and into another, nor can Link attack from one screen into another. Thus, each screen represents a self-contained segment of gameplay, rarely dependent on what came before it.

Enemies are generally very “stupid” and normally just follow set movement patterns. Outside of bosses, few of the enemies actually pursue the player, and most are killed in one or two hits from the player’s sword. Most enemies attack the player with “contact damage,” though some launch projectiles along whatever direction they are facing. Often, enemies leave behind some kind of reward on their death, usually a coin (or “rupee”), heart (representation of Link’s life or hit points) or other refillable items (arrows, bombs, keys).

Of course, all of this is probably not news to anyone reading this, as I would hope everyone is familiar with this classic. It can be easily located in ROM form to play in your favorite NES emulator, or you can grab the version for the GBA (the re-released NES classics). I have both, in fact!

Our first topic (which will be posted either later tonight or tomorrow night) will be some observations on the movement and attack mechanics of Link.

Raph Koster teaches the Theory of Fun. Eric Zimmerman teaches the Rules of Play. Chris Crawford teaches the Art of Interactive Design. But they all need to take a step back and look at the bigger picture, the underlying psychology — not the “what” of games, and more generally play, but the “why.”

A Theory of Games for Just About Everyone by Aaron Ruby

Excellent article. In fact, so good that I am already eagerly anticipating the next article (he’ll have a series at Next Generation). Yes, so good that I am actively lamenting the fact that I think I gave away my copy of Smartbomb without reading it… To be honest, from the book’s cover (yes, I know I shouldn’t have judged…) and based on who gifted it to me, I had assumed (yes, I’m an ass) the book was more business, more shallow and less practically informed than what I’d be interested in. If it’s anything like this article, than I made a serious mistake.

Aaron suggests that play is part of what philosophers call “intentional attitudes.” While Koster, Zimmerman, Crawford, et al, prefer to define play (and by extension, games) through the physical actions that compose play/games, and by the context in which they occur, Aaron rises above those definitions and points out that play, like art, really is in the eye of the beholder. In other words, play is defined by the player, not by the specifics of his actions.

I absolutely agree with this definition, and I also agree with Aaron’s suggestion that by applying this definition, by looking at our medium through this lens, we can better understand both when/why we are successful with certain elements and in certain contexts, and where we can go to broaden our medium.

How can you argue with a definition that encompasses football, SimCity, Doom, Barbies, D&D and sex?

Last spring, I decided that the next game I work on should have user interface metrics. By this, I mean I would gather metrics on how the user interacts with the game (where they move the mouse, where they click, when they click, etc.). Given a deterministic game engine (which is how I generally like them to be), one could theoretically playback the UI metrics log to reproduce the exact game session. While I hadn’t spent a lot of time thinking about specifically what information I would gleam from this data, it sounded like a useful (and interesting, and lightweight) metric.

A few weeks ago, I saw this cool utility of TechCrunch: Clickdensity. With just some simple JavaScript inserted into your web pages, Clickdensity builds heatmaps for your web pages. Very cool. I saw another bunch of script earlier today (can’t find it now, though), and just now saw a mentino of CrazyEgg, which does the same thing as well.

And to complete this meme, today on Gamasutra was this fine article on RTS interfaces, Too Many Clicks! Unit-Based Interfaces Considered Harmful. Around page 5 or 6 he makes the suggestion of user interface metrics, describes weighting them, and even provides some references on prior research in the topic.

How’s this more broadly useful to games, particularly the heatmap tools? Well, first of all, games are all about interface design. A game’s UI can make or break its usability, and by extension, its fun (as opposed to it becoming a chore). A heatmap can reveal those parts of the UI where the players consistently click with some expectations but are left wanting. They can also indicate organizational problems: if you have a big cold spot in the middle of your UI, then it’s a likely candidate for simplification. Or, if you find a stray UI element that is consistently as hot as your main UI elements, then perhaps the two need to be better integrated (or at least brought spatially closer).

Given the proper UI metrics, one could look at them plotted over time, specifically their frequency. The developer would want to closely investigate any spikes (or valleys) as they are potential indicators of pacing issues, or confusion on the part of the user.

[Update: I found the other clickmap/heatmap site I mentioned above: The definitive heatmap.]

I was commenting yesterday on Patrick’s blog about interactive storytelling. As evidenced by my multiple comments, I was having a bit of trouble expressing my opinion. Thankfully, Ernest Adams came to the rescue with an article today over at Next Generation: Secrets of Interactive Storytelling.

First, the storytelling I described in the aforementioned comments would fall under Ernest’s label of “emergent” storytelling (duh). Second, he boils down gameplay into three phases that neatly explains what I was trying to get across… that from the player’s perspective, all stories are linear because time is always moving forward. The debates in the interactive storytelling community are really all about the implementation of the storytelling, not the definition of it.

Something I’ve found difficult to reconcile lately is a sneaking suspicion that interactivity is not a source of emotion, in games or in real life. Rather, emotional responses come from reflection on past actions or anticipation of future actions, but action itself does not seem to spur emotion.

You may think I’m splitting hairs, but think about the most basic emotional response, fight-or-flight, one that is fairly universal in the animal kingdom. This is the basis for most “violence” oriented games (and action movies). The literal rush of adrenaline that underpins fight-or-flight is not a byproduct of actually fighting or flighting, rather it’s triggered by the anticipation of having to do either. Surprise is an emotional response that basically results from the fight-or-flight mechanism having to catch up with an action that’s already occured.

Sex, well, it’s even more basic and instinctive than fight-or-flight (or at least equal). As has often been stated, anticipation of sex contributes as much or more than the actual physical act itself to the emotional response. Sure, sexual “interaction” has plenty of rewards built-in that go hand-in-hand with the participants’ actions — (god that sounds dry and academic) — but most of the instantaneous ones are mechanical in nature and not necessarily emotionally driven. In other words, thinking about sex elicits the emotional response, having sex elicits the physical response.

That’s where movies (and most non-interactive art) have the leg up on games: they’re all reflection or anticipation, all the time. Because the audience does not have to actively make decisions they get to switch into a continual alternating cycle of reflection and anticipation. Those are the fundamental components of drama.

Games, on the other hand, necessitate breaking the reflection/anticipation cycle by needing to insert interaction at some point. The drama doesn’t come from the interaction itself, but rather from the bookends of the interaction: either reflecting on the actions you took (or their results), or anticipating the actions you (or others) will take (or their results). This is why drama is almost universally seen in only the cutscenes, or more broadly, the narritive parts of games; it’s the point where the game formally reflects on or anticipates past or future actions.

Of course, drama does occur at the meta level of the game. As a player, you have a train of thought and awareness that runs parallel to your avatar in the game. While the avatar is acting out mechanically in the game world, even as you actively control those actions, you are passively “experiencing” the game as would a non-participant. In other words, game players simultaneously participate in and act as audience for their games.

The misguided pursuit is the idea that we can create game mechanics or interactivity that is emotional. The common wisdom is that “innovation” will provide this one day. Of course, while most focus on innovation as new mechanics, I’ve previously made it clear that I don’t think our mechanics are necessarily the failure. It’s not the interaction that will spur the emotional response, it’s what the player does before and after that ineraction that will bring about the tears and laughs.

In other words, the reason most games have no significant emotional quality is the same reason that a bad movie lacks emotional quality: poorly developed or unsympathetic characters, poor pacing, stilted acting, etc… The reason games get away with it and movies do not is because movies rely on drama as a defining element, whereas games rely on interaction as a defining element. Emotions are just icing on the cake, like good photography or special effects in a movie.

So, in response to this recent post on game girl advance (Sex Games Should Make You Feel Sexy… Right?), I’d argue that we shouldn’t be worried about whether or not the mechanics in a sex game become unsexy. Honestly, the mechanics in real sex is pretty unsexy. The emotional response, the “sexy” feeling, comes from the context surrounding the mechanics, the anticipation of the act, and the reflection on the act the next morning.