S.T.A.L.K.E.R.: Shadow of Chernobyl Designer Diary #4

While first-person shooters started off as simple, arcadelike games that set you in a first-person perspective and required you to blast everything that moves, GSC Game World's S.T.A.L.K.E.R.: Shadow of Chernobyl will be much different. Yes, you'll play the game from a first-person perspective, and yes, you may be required to defend yourself by shooting the enemy, but the similarities end there. In this unusual action game, you'll play as a "stalker," a scavenger tasked with exploring the ruins of the Chernobyl reactor after a second, fictitious reactor meltdown in the near future, following the unfortunate real-world meltdown in 1986. Your mission is to recover rare and valuable "artefacts"--items that have been bombarded with radiation from the government experiments that led to this fictitious second meltdown--but since you're a lone scavenger, you won't have the luxury of a vast arsenal of weapons. You'll have to carefully conserve everything--your ammunition, your food supplies, and your energy--or risk falling victim to exhaustion, radiation poisoning, or an attack by the various mutant creatures that are rumored to exist in and around the irradiated area. As if that weren't enough, you'll also be in competition with rival stalkers who would like nothing better than to snatch up all the artefacts for themselves.

In addition to featuring impressive-looking graphics that are based on real-world photographs taken at ground zero, S.T.A.L.K.E.R. will also feature realistic, simulated physics. That doesn't just mean that your enemies will flop down convincingly if you shoot them; it also allows for more interactions with the environment, such as using vehicles as transportation (and possibly weapons). This edition of our designer diaries discusses the role of physics in the game.

Making Chernobyl Move

By Anton Bolshakov
Project Leader, GSC GameWorld

With realism being the single most important concept behind S.T.A.L.K.E.R., we knew that we had to focus a great deal of our attention on developing a realistic physics model for the game. We knew that we could make our environments realistic with considerable graphical detail, but to get to that next level, we felt we had to create a whole new physics engine in order to provide truly immersive gameplay. The better our physics engine, the greater that feeling of realism would be.

This completely new physics engine allows us to create an environment in which objects are truly interactive. Chairs, tables, bricks, cans, and many other objects can be pushed, knocked down, destroyed, and otherwise manipulated in ways that feel natural. Whereas many games might limit this interactivity to "quest items," S.T.A.L.K.E.R removes these restrictions so that you can fully explore the world in a realistic manner. One scenario might involve your wearing a headlamp while exploring a dark area. You might bump into a ceiling fixture and get knocked down, and when you get back up, your light will be dispersed by the swinging fixture.

We feel that our powerful physics engine allows for not only realism, but also tactical opportunities in combat or reconnaissance missions. For instance, you might be exploring an area where light is poor, panic on seeing a sudden movement in the distance, and open fire. When inspecting the fallen victim, you may discover that it wasn't a monster, but another stalker--perhaps one that belonged to a rival gang that could turn against you as a result. You may wish to try to drag the body out of sight to avoid detection.

The process of dragging bodies won't be limited only to stalkers, either. Many in-game creatures also possess the intelligence and ability to use objects in this way, so you'll have to learn about the nature of your environment. Some objects will serve as handy ways of stunning or injuring opponents, while others will provide essential defense against explosions or gunfire. Then again, they may not. Not all materials will be able to sustain concentrated fire from an AK-47.

We've paid special attention to body physics, as well. S.T.A.L.K.E.R. has an advanced skeletal animation system that controls realistic body movements at a very high level of detail. Each human character in the game contains about 50 bones, all of which can be adjusted--right down to the pinky finger. Our engine defines human movement based on the maximum tensile strength of bones, joint stiffness, and weight, among other factors. All of this contributes to the way in which a body will react when it is falling or being shot. Watch for the way bullets will even leave trace holes in the bodies. Given this level of detail, we felt we would be remiss not to tie this in to the gameplay. For instance, if you're severely injured, you'll move more slowly. Hand injuries will cause tremors and difficulties when aiming; leg injuries will cause you to limp. It's a liberating experience to utilize physics in this way. We have even set the game so that different types of clothing and weaponry affect the way you'll be affected by gunfire or other factors.

We have, for obvious reasons, given similar attention to the game's weapons--we're modeling the game's weapons after their real-world counterparts to enhance gameplay, so they don't feel like merely new skins. For example, we have modeled the approximate range of each weapon, but this is only the beginning of what the physics engine has allowed us to do. Some weapons will have greater penetration ability, while others will have modeled scatter ranges for burst shots. And virtually any type of weapon can be modified with laser sights, muzzles, or grenade launchers. Realism further dictates that weapons have limited life spans, misfire tendencies, and so on, so you'll often find that when visiting the game's illicit merchants to equip yourself, you'll get what you pay for. Add to this the inclusion of a fine assortment of bladed weapons, and it will be a long time before you get to see the full range of impact types a body can take.

Vehicles will also have their own behaviors, and to keep your vehicles working, you must keep track of your fuel and damage levels. S.T.A.L.K.E.R's vehicles have doors that can open and close, trunk space, and sometimes even glove compartments into which various inventory objects can be stored. Should a bullet hit a tire when a vehicle is moving, that vehicle might get turned upside down or swerve to a halt. Drivers can also be killed as a result of an automotive accident, which can have dangerous consequences for the killer.

Physics are an exciting area of game development that offer players massively extended opportunities for interaction and gameplay. With S.T.A.L.K.E.R., our highly detailed physics engine should make tremendous additions to the overall degree of realism that the game will offer.