X-Ray Engine

The X-Ray engine logo.

The X-Ray Engine is a 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:

• S.T.A.L.K.E.R.: Shadow of Chernobyl
• S.T.A.L.K.E.R.: Clear Sky
• S.T.A.L.K.E.R.: Call of Pripyat

An upgraded engine was planned for the original 2010 S.T.A.L.K.E.R. 2 release. It is now confirmed that GSC will use Unreal Engine 5 instead.

History

The development of the X-Ray Engine dates back to 1998, when two novice GSC Game World programmers: Oles Shishkovtsov and Alexander Maksimchuk - teamed up to work together on their own 3D engine.

By 2000, a demo version of the "Sea Battle" game was released on the engine. From this moment, the long-term development of S.T.A.L.K.E.R. (then named Oblivion Lost) and its X-Ray engine begins.

Overview

The X-Ray Engine is a 3D game engine, supporting DirectX 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.

It also has a unfinished and rather broken Global Illumination function which can be enabled with the console command "r2_gi on". Do note that it will tank FPS significantly to single-digit levels even on top-end hardware today.

Versions

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. X-Ray does not support anti-aliasing but can, however, create a fake form of anti-aliasing when static light is 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

S.T.A.L.K.E.R. - Clear Sky "DirectX10 Features" trailer

X-Ray 1.5 DX 10 features video.

The improvements made to 1.5 compared to the original 1.0 were significant. New visual effects like volumetric lighting, dynamic volumetric smoke, full volumetric fire, soft water, dynamic wet surfaces' (with water streaming down the side of surfaces), depth of field blur, SSAO, HBAO, HDAO, and DirectX 10/10.1 support.

One of the very noticeable visual effects that the X-Ray engine provided for Clear Sky is the godray/sunbeam effect.

The animation engine also received an overhaul, with many reworks in animation quality and Inverse Kinematics included in the game. NPCs can also use smart covers now, often blindfiring and supporting each other 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.

Features

A.I.

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.

Physics

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.

Bullet physics

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.