S.T.A.L.K.E.R.: Clear Sky
Just Standing Within the game world of STALKER was often a captivating experience: listening to distant howls of mutated dogs and listening to the gentle clicks of a Geiger counter. No other game has delivered such a free-form, AI-driven landscape (or at least such an excellent illusion of it), so it's easy to assume that STALKER has stolen a march on the vast ecosystem of Far Cry 2 by its inclusion of realistic predator behaviour - the latter with nary a lion or hyena in sight.
Not so, patiently explains GSC Gameworld's AI programmer Dmitriy Yasenev, because the complexities of self-governing behaviour run far deeper than that "Basically, creatures in the STALKER systems are just imitating hunger and acting upon it - trying to hunt," he explains. "To construct a true system where creatures feel hunger and can die from it would be inordinately difficult to balance - how do you make sure all the creatures find food and don't die? Messing up the balance could result in deserted levels littered with creature corpses that have died from starvation - as such, in a game world like STALKER'S all the creatures are hunting for food but never die from hunger."
Therefore, while Far Cry 2 sidesteps the issue by nixing non-human predators altogether and implants AI routines to suggest that the occasional lioness is ready to pounce from the long grass, everything in STALKER is at the top of the food chain. This isn't to say there aren't a few AI clevernesses to give the impression of a real ecosystem though.
"If you watch wildlife programmes you'll never see animals eating their prey in the open," explains Yasenev. "They always look for cover in trees, bushes or some caves. The same thing was programmed into the monsters' AI to make it more realistic and atmospheric to observe. After detecting a corpse or hunting down prey they'll look out for the closest appropriate cover and drag the food over."
Fight For Survival
When STALKER was first touted, the mutated wildlife of Chernobyl would not only react in these ways, but also behave differently according to weather patterns, smell and occasional violent mass-migration due to reactor blow-outs.
"Yes, in the final version we only had sight and sound-based behaviour, and a few additions such as a day/night dependence where some monsters would sleep at night," confirms AI diva Yasenev. "With something like smell, it simply wasn't being used on the level of gameplay in the final product. Objects in STALKER have no smell, good nor bad, so as it turns out there was no need."
But what of the open world AI advances of STALKER: Clear Sky? Well, most of it lives and breathes within the strictly boys-only members clubs of the various warring factions of this Chernobyl prequel. The rather primitive factions of the first game have been given a complete intelligence revamp, alongside more distinct encampments and bases with various commanders, mechanics, traders and gruff barkeeps therein. "It's all driven by A-Life," explains Yasenev. "The factions fight over important points' within the Zone, whether it's territories, resources or scientific knowledge. You'll join your chosen faction and see and feel how your actions can help in their Zone-wide war. In fact, your actions and the A-Life system will create your various tasks through what's going on at the frontiers and how advanced you are through the faction's ranks - leading up to missions where you'll be leading assaults on enemy locations, possibly even trying to capture the base of a rival faction.
"We've also worked on a lot of the peaceful AI to make it work hand-in-hand with the environment," adds Yasenev. "There's a whole bunch of animations to liven things up and make NPCs behave more naturally in camps -they bend over campfires to see food being roasted, back off when they're in sudden danger, look up at you as you approach, walk around the camp to find somewhere to rest, patrol the area., and on top of that we've slipped in some nice little extras, specifically with artefact generation, weapons and gear upgrades that are all influenced by A-Life."
Clear Sky's clear intent is to mature the sometimes stilted gameplay and AI idiosyncrasies of the original (you won't be able to neatly sidestep a pack of marauding hounds this time for example, the AI will now be able to predict your strafing capabilities and limit canine turning circles) while simultaneously conjuring up something user-friendly and less obtuse.
At this stage of development, with GSC repeatedly assuring us that the game will appear on time and in complete form, it's hard to act the cynic.
Magnanimous in victory? Well, not really..
One of tlie coolest AI behaviours in STALKER: SOC was the way that after a battle between stalkers, tlie victors would calmly proceed to finish off the wounded with blasts to the head. How did that come about?
"At first we liad no wounded state at all, people were either alive or dead," explains AI programmer Dmitriy Yasenev. "But then we added the wounded state and faced a new problem - sometimes stalkers would scurry around trying to find that one wounded guy during combat. Hie next step was to make them ignore unconscious enemies if there were other enemies around - but once combat was over the victors would all rush to the wounded to make a final shot. It was really funny - this five-man group scurrying around trying to find one nearly dead and motionless enemy to shoot Ultimately, we created a system that chose just one stalker to finish off the enemy."
Download S.T.A.L.K.E.R.: Clear Sky
Systems: Windows 9x, Windows 2000 Windows XP, Vista, Win 7, Win 8, Win 10.
Game features:Single game mode