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Rags to riches

Kicking a lump or two out of ragdolls, the fall-guys of gaming

You've got to admire those flippy-floppy folk known as ragdolls. When we're not shooting them in the skull, we're piling them on top of each other like prisoners in Abu Ghraib, or throwing them down staircases in exquisite slo-mo.

PC gamers often add to their mental anguish by stripping them and leaving them to rot with their heads in their crotches. Like pulling the wings off flies or reading Heat magazine, this is morally dubious, but it's also part and parcel of playing PC games. Isn't it about time we gave these living dolls their dues?

Dr Steve Collins, co-founder of Havok (the physics boffins whose engines have powered countless PC games, from Company of Heroes to BioShock), reckons so. "If you want a convincing portrayal of a character that interacts realistically with other characters or with the world around them, then ragdoll technology is a critical component," says Collins, who left Havok in 2005 to teach game technology at Trinity College, Dublin.

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IT'S A DOLL'S LIFE
The proof is in the interactive pudding. Some of the greatest PC games of modern times - Hitman, UT, Max Payne 2, Half-Life 2, Far Cry and STALKER - use ragdoll physics to fantastic effect.

Half-Life 2's Source engine made bad-guy death throes all the more convincing. Counter-Strike: Source wouldn't be half the game it is without ragdoll physics, while Garry's Mod is some kind of Newtonian wet dream.

And yet, like Britney Spears, there's something not quite right about ragdolls. More often than not, the instant a game character 'dies', it transforms into a flaccid amoeba, flopping about on the floor and folding into origami shapes without even a nod to human anatomy.

Then again, even fully animated characters in games are fraught with problems, as Dave Gargan, principal engineer at Havok, points out: "Game characters continue to run as they face walls. They don't have any subtlety.

"They don't bang their shoulders on doorposts and they don't place their hand on a wall to support themselves as they peek around corners."

With such issues to address in the living, it's hardly surprising that the dead in games adhere so loosely to reality.

But while ragdolls are still in the early stages of their evolution, they're actually celebrating their 10th year of existence. Mark Healey, creator of Rag Doll Kung Fu, recalls seeing a piece of software around 1997 where players push dummies down staircases. "Completely pointless, but hours of fun," he muses.

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A year later, the Spielberg-endorsed PC game Jurassic Park: Trespasser brought ragdoll physics kicking and flailing into the mainstream. The dinosaurs in Trespasser were made up of rigid-body systems and used inverse kinematics to move, as well as pushing away from one another when they collided.

Although the ideas were advanced for the time, the game was slagged off for being way too buggy. "Many people now see Trespasser as an example of how not to do physics, but frankly this was probably the single biggest leap in physics technology in games to date," reckons Steve Collins.

Collins notes that the idea of linking rigid bodies to create dynamic systems - this is what a ragdoll is, essentially - wasn't all that new, even in the late '90s. In the 1982 Atari game Gravitar (later remade into Thrust for the BBC Micro and Commodore 64), you navigate a lunar-lander craft, pick up pods with a grappling device and negotiate a cave system.

"This involved a simple dynamic system of two rigid bodies - the ship and the pod - connected by a single constraint. The pod acted as a heavy pendulum connected to your ship, which made movement very tricky. In terms of simulation, this was the 2D equivalent of a single limb (like an arm)."

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