Developer Commentary (Left 4 Dead 2)

The Developer Commentary is an extra mode in Left 4 Dead 2. In it, the player is able to listen to audio comments made by the developers. The comments are activated when the player starts a commentary node via the "use" key, and may skip them in the same way. In this mode, players go through The Parish campaign—with a significant lack of difficulty. Though there are enemies in the game, there are no boss Infected unless the player has spawned them by a node, and the common Infected generally ignore the player until the finale, instead going for the other Survivors first (if all of the others are dead, spawned Special Infected will target the player). Due to this, no achievements may be earned, but it is a way of practicing a number of skills.

The Waterfront
Number of Nodes: 11

Welcome
[ Node next to the starting point ]

[Gabe Newell] Hi, my name is Gabe Newell, and welcome to Left 4 Dead 2. We love this style of zombie-driven cooperative gameplay. Tom Leonard and the rest of the Left 4 Dead 2 team had a great time building on the design and game mechanics of the original and we hope you have as much fun playing the game as we did making it. 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 key again to stop the commentary. Please let me know what you think after you have had a chance to play Left 4 Dead 2. I can be reached at gaben@valvesoftware.com. I get about 10,000 emails each time we release a game, and while I can’t respond to all of them, I do read all of them. Thanks, and have fun!

Campaigns
[ Node in front of the fence ]

[Scott Dalton] We did a lot of work in Left 4 Dead 2 to make every campaign unique in terms of flavor and game play. This drove our decisions in regards to locale, lighting, population, music, and events. We wanted to create a continuous set of locations proceeding through the South, with the key goal of making each location iconic and evocative. We drew up an overall world map of our version of the South, and charted out a journey through a variety of locations. While each location has its own particular common zombie types, we also further differentiated each campaign by creating "Uncommon" zombies that were thematically tied to that location. The uncommon zombies also had specific game play mechanics that made them unique. In each campaign, the music blended specific elements of the location with the central recurring Left 4 Dead theme. We also designed new elements in each campaign where the Director could take control in interesting ways--be it weather, unique paths, or types of Crescendo Events and Finales.

Wound System
[ Node in front of the market entrance ]

Note: This node repeatedly spawns Common Infected.

[Gary Horsfield] Since players spend the vast majority of their time shooting the common infected, we wanted to improve the feedback and visceral nature of this experience. In Left 4 Dead 1, we provided only the ability to shoot off limbs with blood decals for bullet hits appearing only on the PC. Now, in Left 4 Dead 2, there are 43 unique ways to damage an infected--from gunfire through melee weapons, all the way up to explosive damage. Because many of these wounds are non-fatal, players are able to wound an infected more than once, resulting in about 780 possible damage combinations. To create the appearance of a wound, we project a texture modified by an ellipsoid that culls the pixels of the wounded area from the infected, creating a cavity for the wound to fit into. To avoid memory overhead, instead of creating wound variants for each of the infected, the wounds are spawned as seperate objects that work for the entire horde. Our scripting system allows us to spawn specific wounds from specific weapon hits. For example, the sniper rifle headshot explodes the head, and the axe creates a slash across meaty areas of the body.

Body Piles
[ Node over a body pile ]

[Marc Nagel] The body piles were generated by tossing self-colliding ragdolls into a level in-game, then exporting out the result. We were able to use a debugging tool to drag them into artistic piles -- content creation at its most enjoyable. Unfortunately, the process was so efficient that it took only about two hours.

Sound Design
[ Node on a balcony overlooking the street ]

[Mike Morasky] The guiding sound design principles in Left 4 Dead 1, as well as Left 4 Dead 2, were to stay as organic as possible and to reflect the world within which the game takes place. For example, the monsters are all former human beings, grotesquely transformed; and as such, all of their vocalisations are human performances with very little effects processing, if any at all. The challenge with the new character sounds in L4D2 was to keep them clearly audible for game play, reasonably believable at unrealistic distances, and clearly identifiable as unique. The existing bosses already used the pitch spectrum for differentiation, so we expanded into more characterizations. The Charger mutters unitelligibly to himself; the Spitter is trying to screech out her bile hairball; and the Jockey...well, who knows what he's on about?

Enemy Variation
[ Node next to the broken-down bus ]

Note: This node repeatedly spawns a group of Common Infected.

[Ricardo Ariza] We wanted to improve the variation on the infected while keeping their memory footprint identical. The entire horde is never comprised of more than five head textures and five body textures. We use a luminosity lookup into a gradient texture for tinting variation, allowing us to get not only hue variation but also luminosity variation; for example, we can make black or white t-shirts out of the same texture map. The gradient is broken up into zones, so that we can tint areas of clothing and skin differently. The infected texture also includes four distinct masks for blood and details such as dirt or pond scum. We randomize both the gradients and the masks each time an infected is spawned. We also randomize the body and the head meshes, resulting in nearly 20,000 available variations in a typical map--up more than ten-fold from Left 4 Dead.

Music
[ Node next to the jukebox in the bar ]

[Erik Wolpaw] When deciding what to do with the music for Left 4 Dead 2 we faced some interesting challenges. Some of the music in Left 4 Dead 1 plays an iconic and important role in game play, and we felt that it shouldn't really be changed. On the other hand, the game is set in the Southern United States, which is rich with musical identity, so we also felt that adding some local flavor to each campaign would really help set the tone for that campaign. The solution to bridging the gap between the new "local" campaign music and the more traditional horror music from the first game was solved in several ways. First, we kept all the original themes from Left 4 Dead 1 but arranged them in a style consistent with the local campaign's theme. Second, we wrote an overarching set of cinematic "southern goth" pieces for the entire game. Finally, we wrote new pieces for the new characters in the style of Left 4 Dead 1. By doing all this, we establish that these are new characters in new places but they are sharing the experience of everyone else in the Left 4 Dead universe.

Infected Textures
[ Node in a back alley behind the bar ]

Note: This node spawns a Common Infected.

[Bronwen Grimes] The infected textures are part hand-painted, part photographic reference. One of our team members had a nightmare folder full of photographs of people suffering from bizarre diseases and injuries. They were so hard to look at that the infected actually contain none of these. Instead, the secret ingredients for infecting normal-looking human textures are photos of housing insulation and potato skins.

Glowing Details
[ Node in the back of the kitchen ]

Note: This node spawns a Common Infected, a Hazmat-suited Infected, and a Worker Infected.

[Thorsten Scheuermann] We wanted to invoke the feeling that the infected have lost their humanity and behave like feral animals. Seeing their eyes glow in the dark like those of a deer in headlights helps illustrate this. To create that effect we authored the shader for the infected so that an artist could mark the regions that should reflect light towards the viewer in a texture. The artists quickly realized that they could also use this feature to make retro-reflective safety materials on clothing, which they put to use on several of the uncommon characters. You now see this effect on riot gear, CEDA hazmat suits and construction vests. As a side-benefit, we found that the retro-reflective effect also helped players identify targets in very dark areas.

Explosion Debris
[ Node in the restaurant ]

[Sergiy Migdalsky] This restaurant was one of the first areas we populated with tables and chairs. In early playtests, a Survivor would pop a Boomer, and the resulting explosion sent tables and chairs flying everywhere. It was a great effect. We decided to furnish a few more areas like this, so that more players would be likely to experience it at some point in the campaign.

Pipe Bomb
[ Node outside of the safe room ]

[Torsten Zabka] The pipe bomb has always been a crowd pleaser, but in Left 4 Dead 1, we were forced to disable ragdolls and gibs and replace them with a blood mist due to performance issues. This time, with a new wound system, a new ragdoll solver, and new particle effects, we've finally returned to our original vision. The pipe bomb causes visually catastrophic damage to the infected horde, to the delight of gamers and designers alike.

The Park
Number of Nodes: 13

The Cemetery
Number of Nodes: 10

The Quarter
Number of Nodes: 13

The Bridge
Number of Nodes: 10