Excerpt

DAVE BREVIK'S MORNING ROUTINE WAS crucial to Blizzard North's success. After rolling out of bed, he dragged himself into the shower and cranked the hot water to full blast. Closing his eyes as steam curled up around him, he rested his head against the tiled wall and let his mind wander. After a few minutes, his eyes popped open. He scrubbed and dressed quickly, hopped into his car of choice, and raced to Blizzard North, where he strode through the front doors and into the bullpen, face aglow.

Programmers greeted him with a mixture of excitement and trepidation. "Even though he was a programmer and I was an artist, Dave Brevik is someone I view as a real talent in the industry," said Eric Sexton. "His unique vision really inspired me. At least two or three times a week, he'd come in, like, 'I was taking a shower, and I had this idea.' And he'd tell you the idea, and you were like, 'That's amazing!' Then he'd sit down and do it, and within a day he'd have this amazing idea up and running."

"It wouldn't always be major," Dave Brevik added. "Sometimes there were things like, we really need some extra tests. I'd stand next to somebody's desk and talk to them about this idea I had in the shower."

One late morning, Tyler found himself in Dave's crosshairs. "He said, 'We're not going to load in between levels anymore. Tyler, you can make that happen.' I said, 'Uh... okay.'"

Dave's latest proclamation came from his time playing Ultima Online. As much as he liked the game, he never shied away from pointing out its flaws. Excessive load times was one of his more frequent complaints. Staggering in its scope, Ultima Online divided its world into discrete zones. Most players still had dial-up modem connections in 1997, and could only send and receive data so quickly. When players left certain areas, the game briefly paused and loaded in the next zone. The original Diablo also had to load between levels.

Zoning was slow and cumbersome, Dave Brevik declared. In Diablo II, players should be able to roam from region to region with no breaks in the action. Tyler got to work on a solution. His approach was to simulate only what players could see on the screen. Terrain out of view is rendered when players come within a certain range. Monsters stand idle until they detect players.

There are exceptions. Players can leave fallen trinkets and piles of the gold on the ground, explore and fight elsewhere, and then return to pick up dropped goods. Certain monsters, such as those with ranged attacks, notice players sooner than others, enabling them to lob arrows, spells, or other attacks ahead of time. As players move, algorithms sew tiles together quickly so players never detect the stitches connecting each square.

"You can outrun a monster and it would just stop, because we didn't care about it anymore," Tyler explained. "Then what's left behind is cached and made rather small, so we don't have to worry about it. So, levels would be made as you go, and it'd become more and more detailed."

Algorithms weave tiles into quilts of fields and pastures, caves and temples. Dirt trails connect regions like beads on a necklace, so players can find the way forward once they tire of exploring by returning to the beaten path. Areas are divided by barriers that fit the environment, such as low stone walls in meadows or streams, and crossing those barriers leads to the next zone. The name of an area pops up on the screen as players into it, feeding their sense of discovery and progress. Loading screens only pop up when players travel between Acts, and even then the game's code keeps loading brief.

Perspective Mode, a pseudo-3D display mode available to players with certain 3D graphics cards, was another of Dave's eureka moments. "As we worked on the project, 3D was really becoming a thing. It seemed like everybody was going 3D. I worried that the game would come out and look dated because it wasn't 3D, because 3D graphics had rapidly advanced over the course of the project."

Although the team had settled on building Diablo II as a 2D, pixel-art game like its predecessor, Dave wanted to tap into the burgeoning graphics card market by including special features. A solution occurred during a shower one morning. Like the original game, Diablo II unfolds on a grid, with one major difference: Each diamond-shaped tile is composed of several smaller diamond tiles. Whereas Diablo only accommodated one actor—objects such as player-characters, monsters, treasure chests, items, and so on—per tile, Diablo II's smaller-tiles-within-tiles approach let actors squeeze together.

That granular approach facilitated Dave's pseudo-3D solution, which he called Perspective Mode. Every mini-tile stored a bit of texture so it would blend in with other mini-tiles: grass, dirt, sand, and so on. Dave's idea was to rotate the texture in every miniature tile just a smidge as players moved around the screen. The game passes those textures to the video card which paints them onto two polygons and then stretches them vertically and horizontally so they appear larger or smaller depending on the player-character's position.

Rotating and stretching a single texture wouldn't register to most players, but manipulating every texture on the screen produces a 3D-like effect. As players move closer or further away from any object, the textures stored in polygons scroll by at different speeds, creating a parallaxing effect and giving players the impression that actors are larger or smaller. Objects shimmer slightly, the result of bilinear filtering, a process baked into graphics cards that smooths out textures when objects are rendered larger or smaller than their native resolutions.

"It was doing real, 3D math, and making this grid scale slightly, stretch slightly," Dave explained. "It gave a real sense of depth to the world."

Dave wrote Perspective Mode in a short span of time and rolled it into the latest build of the game. "There were a bunch of things I had to do to make sure walls lined up properly, and the lighting, but I think I wrote that fairly quickly," Dave continued. "I think it only took me a week or two to get it working. People loved the way it looked, and it really was awesome, but the artists weren't super happy they had to go back and chop up things and render them differently. We did feel it was worth it in the end, and added a lot to the game."

Perspective Mode was a relatively quick addition compared to other shower-time epiphanies such as seamless environments. Dave's most impressive idea revolutionized action-RPGs.

One knock against Diablo was that its three heroes were virtually identical. Warriors cast spells slower than the Sorcerer who swung melee weapons slower than the Warrior. But players who chose a Warrior could still cast spells by boosting his magic attribute, while Sorcerers could still swing swords and fire arrows by upgrading strength and dexterity, for instance.

In effect, the three heroes represented starting points. Some critics and players argued that their choice of hero was meaningless. Blizzard North disagreed. The design of each hero—the Warrior's square jaw and toned physique, the Rogue's slim, dexterous build, the Sorcerer's silver hair and wrinkled, wizened face—made the game accessible, their top priority. Players unfamiliar with RPGs could take one look at each hero's profile and immediately gravitate to one that suited their play style. The Warriors were initially equipped and built to play best as a melee fighter, but if players controlling Warriors decided they wanted to throw fireballs or turn demons to stone down the road, they could boost their Magic stat. This was seen as a fair compromise between the sheer creativity of D&D character creation and the desired accessibility of the design team.

Over time, the game's community pinpointed the Sorcerer as the best choice. His fast cast rate and higher maximum Magic attribute gave him access to the game's most advanced spells, especially Mana Shield, a sorcery that let him use his pool of Mana energy as health. Because players who rolled a Sorcerer usually had more Mana than health, Mana Shield made them nearly invincible, robbing the game of much of its tension.

Diablo II's designers decided each hero would have dozens of skills available only to them. The only question was how players should learn skills as they progressed. "I remember the shower where I had the idea," Dave said. "It just dawned on me one day: What if player classes could choose a path through a tree?"

Dave loved games like Master of Orion, which hailed from the 4X strategy genre: Players eXplore environments, eXpand their influence by building new settlements, eXploit resources to fund their colonies, and eXterminate opposition. Master of Orion gave players a deep research tree, a mechanic introduced in the board game Civilization by Francis Tresham, which shares no relation with Sid Meier's Civilization, the computer game widely credited with popularizing research trees in video and PC games.

Skill trees promote organization and accessibility. Buying one upgrade lets players learn a new skill, and unlocks more advanced upgrades further down branches of the tree.

"I came into work and told Erich. I think this all was around the [development of] StarCraft," Dave said.

Originally, Dave wanted to hew close to Master of Orion by giving characters a skill tree composed of dozens of abilities. The resultant design would have been less a tree and more a tangle of branches that would have been too complicated for players to follow. Stieg Hedlund sanded down the idea's rough edges. "While I was taking a break from Diablo II and working on polishing StarCraft, we [both Blizzards] made a tech-tree poster," Stieg recalled. "It was literally a tree in that it started at the bottom and involved the interdependencies of buildings and units."

Stieg wanted to transplant the concept of tech tree posters into Diablo II's user interface to more clearly communicate what players could do with their character. He went to Dave, Max, and Erich with his layout idea. They settled on thirty skills per hero, divided evenly between three trees. Skills are arranged vertically, with low-level skills at the top giving way to more advanced skills at the middle and trailing down to the cream of the crop at the bottom.

Over months of iteration, the Amazon's skills were ordered into Javelin and Spear, Bow and Crossbow, and Passive and Magic trees.

"'Let's start by making an archer-type character who can maybe also throw spears,'" Dave Brevik recalled of brainstorming the Amazon's trees. "We figured if we're going to have range, maybe she can shoot arrows and use javelins and spears."

The Amazon's Javelin and Spear and Bow and Crossbow categories are easily understandable. Players interested in building out a character that specialized in ranged attacks, a la Diablo's Rogue, should focus on Bow and Crossbows. The Passive and Magic tree contains an assortment of defensive abilities such as an increased chance of dodging projectiles and melee attacks, and the ability to create a decoy that diverts monsters' attention away from the player.

Skills added layers of tactical play and personality-driven customization to progression. Players level up by killing monsters and completing quests to earn experience points. Every time they gain a level, players receive five stat points—to increase Vitality, Strength, Dexterity, and Energy, the magical force for deploying skills—to distribute as they see fit, and a single skill point. How they spend that point is up to them. One or more branches connect some skills to others, communicating to players that they must first invest at least one point in a prerequisite skill to learn a stronger ability later.

Although low-level skills start out weaker than high-level abilities, players can upgrade each skill up to twenty times, scaling it to to assist players in tougher battles late in the game. Alternatively, players can spend the minimum amount of points on prerequisites and save points for high-level abilities, or distribute points far and wide across one, two, or all of their trees to create hybrid characters proficient in an array of techniques. One Amazon player might go deep into the Bow and Crossbow tree to unlock its full potential. While another player might spread a few points across the Passive and Magic category for abilities such as Inner Sight, which lowers enemy defense, but mix in Javelin and Spear spells for melee combat. Yet another may invest in all three trees, not going too deep into any one specialization, creating a generalist character able to swap between an assortment of weapons at a moment's notice.

"I tried to pay off on the fantasy of each of these classes, the things that people would tend to associate with them as archetypes," Stieg explained. "I wanted all the classes to be [able to finish the game solo], but at the same time to have strategies that were effective and ones that weren't. Running into a room full of bad guys with your Necromancer should be a pretty bad idea, as it's contrary to what he's all about, and I endeavored to make sure this was the case in the game."

While Stieg and the three bosses were the first to brainstorm skills, Blizzard North's egalitarian culture permitted anyone to chime in. Erich Schaefer pruned tree layouts, collaborating with Stieg, Dave, and programmers such as Tyler Thompson who, along with Theodore "Ted" Bisson, coded skills. Sometimes a developer would jot down the name of an ability and a suggestion for what it could do. Most notes, such as the direction Tyler received for the Necromancer hero's curse abilities, were vague, leaving plenty of room for interpretation.

"Like, Amplify Damage: it increases how much damage you're going to do," he remembered of one note. "Well, what is that? Is it a percent? Is it for normal damage? All damage? How about damage over time? How does all that work? None of those questions were filled in by a designer. Those were all programmers going, 'Well, this is what seems reasonable to me, so I'm going to do this.'"

Tyler printed out each skill tree once its design was semi-complete, pinned it to a corkboard near his computer, then inserted colored pins to keep track of which ones he'd worked on. If a skill tree's layout changed, he'd have to start over. The position of a skill in a tree determined its ranking relative to every other skill, necessitating a fresh look at how any skill worked.

"Designing skill trees was a lot of work but a lot of fun," said Erich Schaefer. "It was maybe the hardest thing to do, design wise, both creating them and balancing. We'd have meetings and decide what kinds of skills we wanted to do. I'd do rough layouts and we'd try some out, and half of them wouldn't be very good. We redid those trees over and over again. It was just brute force."

"We wanted to put cooler stuff toward the bottom, so we'd say, 'Oh, yeah, that uh, that seems like a level-15 spell. Yeah,'" Dave Brevik recalled, laughing. "Skill trees would change and Erich would design trees multiple times over because new ideas would come in, and things would either work or they wouldn't. Eventually we came up with the theme of the different tabs and stuff, and that all kind of solidified. It was a very iterative process."

Phil Shenk agreed. "It was very collaborative. So collaborative that I can't even remember where certain things came from,"

Stieg juggled ideas for skills with tweaking values recorded in spreadsheets. He claimed the Amazon as his favorite character in Diablo II because of her blend of close-quarters and ranged abilities. "A lot of this does come from her being first, feeling how my goal of allowing the different progression paths was starting to work with her. It's also just one of my favorite character types with the mix of ranged and melee combat."

One of the most distinct heroes was the Paladin, the second class conceived. The character model, painted by Michio Okamura and animated by Kelly Johnson, is a dark-skinned man who walks with a noble bearing. He starts in simple clothes but, as players push deeper into the world, the paper-doll system depicts his armor as gleaming mail that transforms him into a holy knight. "The Paladin was based on the idea of counteracting the devil aspect of Diablo," explained Kris Renkewitz. "Basically, without putting a religious bent on it, we put a religious bent on it."

Another Paladin skill tree lets players learn auras, visual effects that grant passive bonuses to players and their allies such as restoring life, causing enemies to harm themselves every time they strike players, and freezing monsters with cold snaps that slow their movement.

Auras were not part of the Paladin's repertoire at first. The character was almost entirely combat-oriented until Dave gleaned inspiration from Sony Online Entertainment's EverQuest. He tended to play a Bard, a class able to heal and buff other players by playing music, while Mike Scandizzo, a programmer, teamed up with him as a Druid. "Dave started to like the Bard's songs enough that at one point, when he decided the Paladin was not working out, he said we'd scrap all the skills and take some of the ideas behind the EverQuest Bard," Mike remembered. "But instead of songs, we'd make them auras and apply them to the Paladin class."

Dave's ideas were double-edged swords: Everyone saw their potential, but implementing them often added weeks or months of work. "Every morning we'd talk about what we were doing, how the bugs are, what we need to do for that day," Jon Morin remembered. "Then Dave would come in and go, 'I was in the shower this morning and I had this idea.' Whenever we heard that, we'd go, 'Aww...'"

Some programmers remembered Ted Bisson expressing annoyance at all the work they had to toss so the Paladin could be retooled to use auras.

"The Paladin went through major changes," Tyler said. "I think Ted had twenty-something skills that were thrown away before we moved to the aura-based system. That's part of development: You throw stuff out there, and it works or it doesn't."

Ultimately, however, auras passed the Blizzard North test: If a proposal's merit held up after testing, it made the cut. Auras became a defining characteristic of the Paladin. His assortment of combat skills and defensive auras enabled solo players to survive and thrive on their own, while players sought Paladins on Battle.net for the benefits their auras granted to parties.

To fully upgrade each of any hero's thirty skills would require 600 skill points. The maximum character-level is 99, meaning players will never receive enough points to master—fully upgrade—all thirty skills. That limitation forces them to make hard choices: maximize proficiency in a few skills, focus on a half dozen, or potentially spread themselves thin to become competent in all abilities but a master of none. Because each hero's skills are exclusive, all players wind up specializing by choosing a class. From there they only specialize further, investing heavily in some skills, spending a single point in others to satisfy requirements for later abilities, and ignoring most of the rest.

Those limitations encourage them to think carefully about upgrades. The thought they put into skill points creates a bond between players and their avatars, and the satisfaction that comes from seeing a character evolve—and choosing every piece of a character's equipment load—feeds into Dave Brevik's peacock mentality: No two players were likely to spec out the same hero. In fact, a single player could roll several Amazons or Paladins and develop each differently.

Assigning exclusive skills to Diablo II's heroes was more limiting than Diablo's spell books, which could be read and cast by any of the game's three heroes as long as players dumped enough experience points into their Magic stat. Blizzard North's team saw that limitation as a good thing. It fostered agency, asking players to play an active role in evolving their characters.

"They'd pick the Warrior and go in and start casting spells," Dave recalled of Diablo players, "then say, 'This game's just too hard.' And it's like, well, that's because you're not doing the thing you should be doing. So we figured, in Diablo II, let's take the ability for them to screw themselves out of the game by giving them something [more defined]. They would say, 'Oh, I know what a Paladin is supposed to be' or 'I know what a Sorceress is.' They could kind of understand what those classes represented to begin with. Then what they can actually do, and the choices they can make, are interesting and fun."