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 16x16 pixels. Link operates on a half-tile grid, though (32x28 tiles, 8x8 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.