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.
The X-Ray Engine is a 3D game engine, supporting DirectX 8.1/9.0c/10/10.1/11 and Shader Model 5.0. The original X-Ray engine made for Shadow of Chernobyl was developed by GSC Game World's main programmers Oles Shiskovtsov and Aleksandr Maksimchuk.
v1.0 - S.T.A.L.K.E.R.: Shadow of Chernobyl The X-Ray engine features HDR rendering, parallax and normal mapping, soft shadows, motion blur, weather effects and day/night cycles. The engine does not support anti-aliasing but can however create a fake form of anti-aliasing when having static light enabled. It is a technique that blurs out the image to give a false impression of anti-aliasing.
v1.5 - S.T.A.L.K.E.R.: Clear Sky
The improvements made to 1.5 compared to the original 1.0 were significant. New visual effects like volumetric light, dynamic volumetric smoke, full volumetric fire, soft water, dynamic wet surfaces' (with water streaming down the side of surfaces), depth of field blur, SSAO and DirectX 10/10.1 support.
One of the very noticeable visual effects that the X-Ray engine provided for Clear Sky is the sunbeam effect.
The animation engine also recieved an overhaul, with many reworks in animation quality and Inverse Kinematics included into the game. NPCs can also use smart covers now, often blindifiring and supporting eachother in spectacular ways.
v1.6 - S.T.A.L.K.E.R.: Call of Pripyat The new and improved 1.6 is also one of the very first engines to support DirectX 11(mostly in charcter model tesselation and even better shadow quality) and marks a new era in visual aspects of gaming history.
Custom Lost Alpha version A popular standalone mod called Lost Alpha uses a new, unique version of the X-Ray engine. It was originaly based on the 1.0 version used in Shadow of Chernobyl. Some of its advancements include improved multi-core support (best out of all versions), grass shadows, improved DX10.1 renderer, better foliage and rain effects. Unfortunately, it lacks the Inverse Kinematics, DX11 support (tesselation and contact hardening shadows included) and smart cover support to be called a complete upgrade over 1.5 and 1.6 .
The X-Ray Engine uses the proprietary ALife artificial intelligence engine developed by GSC Gameworld. 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.
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.
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.