How Does Ragdoll Physics Work?

Ragdoll physics, or at least the physics engines that have descended from it, is prevalent in many of our game experiences today and yet little is widely known about the animation process that has served up some of gaming’s funniest moments.

Back in the days of static death animation reels, developers were required to plan out a range of possible death sequences which would be assigned to a given situation based on environmental factors. It made for long, hard work, until Jurassic Park: Trespasser introduced procedurally generated animation techniques that left death sequences up to the computer.

A ragdoll character is constructed from a collection of rigid bone structures, held together by a system of constraints based on normal movement of these individual bones. Once the character is triggered as dead, these constraints relax.This makes for death sequences that react to objects around the character, as well as the characteristic ragdoll crumble to the ground.

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gamedev.net

Ragdoll physics has become a somewhat comedic turn of the video games industry over the last decade. Poor implementation of the effect causes bodies to hilariously twist and contort into crude final positions and impossible movements. While admirable use of the effect has been seen in some titles, earliest in Hitman: Codename 47 where it aided the hiding bodies mechanic, it can destroy the immersion and realism of a good experience when used cheaply.

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The effect was greatly aided after its immediate conception however, by the Havok Physics engine commonly associated with Valve games. The engine is the result of an Irish company by the same name that uses dynamic simulation to foster real time interaction between objects in 3D. Accordingly, Ragdoll excels in the incorporation of the environment with the character, but loses out in the realism of the character’s movements itself.

This is where Euphoria kicks in. Developed by NaturalMotion, the Euphoria physics engine is based on Dynamic Motion Synthesis in order to animate the object (or character) as a whole (rather than in individual bone fragments) within the environment. This removes the unrealistic ‘floppiness’ overkill of limbs being over-sensitive to any form of touch, but also prescribes a certain amount of autonomy to the object itself so as to invoke realistic, computer generated reactions to specific events that may occur in gameplay. Euphoria is essentially a progression of ragdoll physics that, while making the process more realistic for the modern eye, still couldn’t exist without its hilarious forefather.

@MusingsTwit

 

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