X-Ray Engine

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X-Ray Engine
X-ray logo.jpg
Developer(s) GSC Game World
Stable release
Version 1.6 / Early 2010
Operating system Microsoft Windows
Platform Microsoft DirectX
Available in English
Type Game engine
Website www.gsc-game.com github.com/OpenXRay

The X-Ray Engine is the name of the 3D game engine created by Kiev-based computer game developer GSC Game World. Released on 20 March 2007, the engine is used in the first three S.T.A.L.K.E.R. games released by the company. An upgraded engine was planned for the cancelled game S.T.A.L.K.E.R. 2. In August 2014 the engine's source code version 1.5.10 became available on GitHub under a non-open-source license.[1]


The X-Ray Engine is a 3D game engine, supporting DirectX 8.1/9.0c/10/10.1/11 and Shader Model 5.0. Up to a million polygons can be on-screen at any one time. The engine features HDR rendering, parallax and normal mapping, soft shadows, motion blur, widescreen support, weather effects and day/night cycles. As with other engines that utilize deferred shading, the X-Ray Engine does not support anti-aliasing and motion blur with enhanced dynamic lighting modes enabled. However, a "fake" form of anti-aliasing can be enabled with the static lighting option; this format utilizes a technique to blur the image to give the false impression of anti-aliasing.



The X-Ray Engine uses the proprietary ALife artificial intelligence engine developed by GSC Game World. ALife supports more than one thousand characters inhabiting the "Zone" (the in-game term for the 30 km wide area of exclusion surrounding the Chernobyl Nuclear Power Plant). These characters are non-scripted, meaning that AI life can be developed even when not in contact with the player.

NPCs have a full life cycle (task accomplishment, combat, rest, feeding and sleep) and the same applies to the many monsters living in the Zone (hunting, attacking Stalkers and other monsters, resting, eating, sleeping). These monsters will migrate in large groups. The non-scripted nature of the characters means that there are an unlimited number of random quests, such as rescuing Stalkers from danger, destroying Stalker renegades, protecting or attacking Stalker camps, and searching for treasure. The AI characters travel around the entire zone as they see fit.

Numerous tactics can be employed to complete the game, such as rushing or using stealth and sniping; NPCs will react in different ways to each of them. S.T.A.L.K.E.R.'s NPCs plan ahead by "Goal-Oriented Action Planning" in order to achieve this.

Bullet physics[edit]

S.T.A.L.K.E.R. uses "realistic" bullet physics, similar in nature to tactical shooters such as ARMA: Armed Assault, Tom Clancy's Ghost Recon Advanced Warfighter, and Operation Flashpoint. Bullets are affected by gravity, bounce against solid surfaces at oblique angles, and firearms are highly inaccurate when fired without aiming. To score consistent hits at medium or long range, players must aim using the iron sights on their guns. Additionally, hit damage is pseudo-realistic, as the player can die after being shot only a few times (although various armor suits and artifacts acquired later in the game increase the player's resistance to damage). Toward the end of the game, a high dependence is placed on scoped weaponry due to the well-armed and powerful enemies that keep their distance from the player.


S.T.A.L.K.E.R. uses a heavily modified version of the Open Dynamics physics engine, supporting hundreds of physics objects on different levels. Ragdoll physics, destructible objects, realistic bullet ballistics and skeletal animation can all be found in the game.


A weather system is integrated into various parts of the landscape and allows a variety of weather effects, such as sunshine, storms and showers.


  1. ^ xray on github.com (August 2014)