The X-ray engine uses GSC Gameworld's proprietary ALife artificial intelligence engine. ALife supports more than one thousand characters inhabiting the Zone. These characters are non-scripted, meaning that AI life can be developed even when not in contact with the player.

The 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. For instance, rescuing Stalkers from danger, destroying Stalker renegades, protecting or attacking Stalker camps or 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. The NPCs will react in a different way 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

S.T.A.L.K.E.R. uses "realistic" bullet physics, similar in nature to tactical shooters such as Ghost Recon Advanced Warfighter or Operation Flashpoint. Bullets are affected by gravity, bounced 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, and the player can die after only being shot a few times (although later in the game various armor suits and artifacts can be acquired that increase the player's resistance to damage). Late-game depends heavily 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 ODE 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. The weapons available, behavior of the AI, game tactics and ranking systems will depend on the weather.

For more direct specifications, check the engine's homepage.

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About S.T.A.L.K.E.R.: Clear Sky with 3 comments by Sclera on Mar 29th, 2011

Allow me to direct your attention to three mods I have recently completed:

1. Clear Sky Music Overhaul

After a few weeks of work and minimal trouble, it's all done. Most of the game's original music has been discarded, since a lot of it was borrowed from Shadow of Chernobyl. Limansk, The Hospital and CNPP remain untouched, but everywhere else gets a bunch of new music. About 59 minutes of music were composed, and (perhaps hypocritically) I borrowed some music from my Shadow of Chernobyl mod as well.

Video preview:

2. Anomaly Sound Replacement for Shadow of Chernobyl

Borne not out of an apparent need for new sounds, but purely out of creative boredom, this mod replaces the most commonly heard anomaly sounds in the game. It gives the game a fresh feel without ruining the intended atmosphere. Also, if you are a mod developer and wish to include these in your mod, please do so, and let me know of course.

Video preview:

3. Interface Mod for Shadow of Chernobyl

I never intended to release this, initially. It started out as a lot of different things I was changing for myself, and ended up being a culmination of these things in a neat little package. The idea of the visual aspect of this mod was to eliminate most of the clutter on-screen, and remove superfluous or immersion-breaking information. On the gameplay screen you can see your health, stamina, current ammo and fire-mode; no, there's no map. That's how I like it (try not to feel tempted to check your Contacts for nearby enemies... I swear I don't do it).

You're given several options here; 2 health bars, 3 cursors, 4 PDAs, and 3 sets of PDA sounds. Don't be overwhelmed though, defaults are installed.

Thanks for reading. Please enjoy my work! Your thoughts are appreciated.

- Rohan

S.T.A.L.K.E.R. Shadow of Chernobyl

S.T.A.L.K.E.R. Shadow of Chernobyl S.T.A.L.K.E.R. Shadow of Chernobyl

Updated 2 months ago Released Mar 19, 2007 Single & Multiplayer First Person Shooter

In 1986, the world's worst nuclear disaster occurred at the Chernobyl power station. Soviet authorities established a 30km 'Exclusion Zone' around this...

S.T.A.L.K.E.R.: Call of Pripyat

S.T.A.L.K.E.R.: Call of Pripyat S.T.A.L.K.E.R.: Call of Pripyat

Updated 3 months ago Released Feb 4, 2010 Single Player First Person Shooter

Call of Pripyat takes you once again into the vicinity of the Chernobyl nuclear reactor that exploded in 1986. This so-called "Zone" is a highly contaminated...

S.T.A.L.K.E.R. Build 1935

S.T.A.L.K.E.R. Build 1935 S.T.A.L.K.E.R. Build 1935

Updated 6 months ago Released Oct 17, 2004 Single Player First Person Shooter

This is build 1935 of S.T.A.L.K.E.R. Shadow of Chernobyl, formally called S.T.A.L.K.E.R. Oblivion Lost. This was made by GSC Game World before they remade...

S.T.A.L.K.E.R.: Clear Sky

S.T.A.L.K.E.R.: Clear Sky S.T.A.L.K.E.R.: Clear Sky

Updated 7 months ago Released Aug 21, 2008 Single Player First Person Shooter

A group of stalkers, for the first time, reaches the very heart of the Zone-the Chernobyl Nuclear Power Plant-and triggers a cataclysm on the brink of...

S.T.A.L.K.E.R: Oblivion Lost

S.T.A.L.K.E.R: Oblivion Lost S.T.A.L.K.E.R: Oblivion Lost

Updated 4 years ago Released Aug 27, 2002 Single Player First Person Shooter

Ones of the first concepts of S.T.A.L.K.E.R Shadow of Chernobyl.

Post comment Comments  (40 - 50 of 65)
Serygala Nov 16 2010, 8:04pm says:

Anyway I can get my hands on some kind of dev kit?

+1 vote     reply to comment
KEVLAR60442 Jan 18 2011, 12:39am replied:

YES YOU CAN! Welcome to 2011!

0 votes     reply to comment
Zachary1748 Mar 20 2011, 5:38am replied:

where can i get this engine?

0 votes     reply to comment
LizardGamer Dec 13 2010, 4:27pm replied:

You can get the mod kit for free but if you want the actual engine you would probably have to consult the creators of it and probably pay for it too

+2 votes     reply to comment
KEVLAR60442 Sep 9 2010, 9:24pm says:

The early X-Ray engine was buggy as hell, and even CoP still has a few glitches, but it produces shaders and lighting that are supererior to even Crysis. I love my shadows, and X-Ray delivers. With some work, the X-Ray engine may be one of the greatest engines of the 21st century.

+4 votes     reply to comment
LizardGamer Sep 1 2010, 4:38am says:

This is certainly a very well built engine. I love how it was constructed, and all the parts in it make it so unique. Even though the first game had bugs and all that, it's understandable as it was the first version of the game engine.

But overall I got to love it. :)

+3 votes     reply to comment
Prypjat Apr 18 2010, 9:18am says:

I like the X-Ray Engine! Its imo one of the best engines ever made! The atmosphere the engine creates is just beautiful!

+3 votes     reply to comment
Frozen442 Jan 6 2010, 12:16pm buried:


hate this engine.again ad again...
this engine is full of bugs! and 1\3 gamers can't play this game,because of "engine crash" every ten minutes! ..and I'm one of them((
you can say "play with static lighting(it seems to play with dx8.1)" - no,this is bad idea.
I like STALKER as a game,it's interesting game,but i hate X-ray engine.

-17 votes     reply to comment
jonas6910 Jan 18 2011, 1:02pm replied:

How much does the players and your's graphics card has MB?32?16?8?

+2 votes     reply to comment
hardcoregamer24 Dec 2 2010, 7:13am replied:

get directx9 and a better computer because i can play without a single crash without a mod. and its the first one get COP instead.

+2 votes     reply to comment
LizardGamer Sep 1 2010, 5:05am replied:

lol what a noob it was the first version of the engine used, the version 1.0. So of course it wasn't the best engine to start off with but it has matured and grown

+1 vote     reply to comment
.id Apr 12 2010, 11:46pm replied:

Maybe you should download a Patch dude !!
It work for me anyway.

+1 vote     reply to comment
SourHyperion1 Mar 1 2010, 8:30pm replied:

are you refering to the STALKER beta? If you are than that's just a retorical question.

+1 vote     reply to comment
Shadow85 Feb 14 2010, 11:40am replied:

Thats different For Call of Pripyat. This game is more sable the its predecessors.

+3 votes     reply to comment
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GSC Game World
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Released Mar 19, 2007
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Mar 23 2011, 1:30pm by .sverek

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