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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Blog RSS Feed Post news Report abuse Related News: STALKER Clear Sky music... and more.

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

Add game Games
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 1 hour ago Released 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 1 month ago Released 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.: Clear Sky
S.T.A.L.K.E.R.: Clear Sky

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

Updated 1 month ago Released 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. Build 1935
S.T.A.L.K.E.R. Build 1935

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

Updated 10 months ago Released 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: 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 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  (50 - 60 of 65)
Frozen442 Jan 6 2010 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 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 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 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 replied:

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

+1 vote     reply to comment
SourHyperion1 Mar 1 2010 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 replied:

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

+3 votes     reply to comment
Mavis130 Jul 16 2009 says:

Great engine, I love the STALKER games...

I just don't understand how non-scripted AI works (I mean, don't they need commands to tell them what to do, and how to behave in combat?).

Oh, and they shouldn't boast about bullet physics until they have seen the mod for Counter Strike: OccupationCS.
EDIT- just found out the ODE engine is free and open source.

0 votes     reply to comment
SirWallyWombat Aug 5 2010 replied:

well its a built in feature not a mod..... but at the time almsot no games hd bullet physics

+1 vote     reply to comment
Daishi2442 Dec 26 2009 replied:

Non-scripted AI works by giving the AI a set of protocols that it can use to formulate a plan to react. In that sense, it is scripted. However, none of the commands for AI is actually given cold-turkey to the AI, and as such is non-scripted.

+2 votes     reply to comment
JuggernautOfWar Mar 7 2009 says:

They need information on X-ray 2.0. That's what Clear Sky uses and it's pretty impressive using DX10.

+1 vote     reply to comment
Catalyst440 Feb 16 2010 replied:


Shadow of Chernobyl uses Xray Engine 1.0, Clear sky uses 1.5 and Call of Pripyat uses 1.6, 2.0 would still be far FAR in testing

+2 votes     reply to comment
noyart Feb 17 2010 replied:

but Call of Pripyat look worst then the first game, it was like going back 5 years of graphic development. I didn't have the same feeling =/

-1 votes     reply to comment
dezodor Online
dezodor Dec 22 2008 says:

there is sdk for shoc.. you can make levels, edit and make models, edit shaders and materials, sounds, anything.

(we are working on shoc levels, check our profile for more info)

as for the cs sdk: its work in progress, release is near.

+1 vote     reply to comment
PureWinrar Oct 8 2008 says:

No sdk tools?

+1 vote     reply to comment
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Released 2007
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Mar 23 2011 by .sverek

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