Editing Ragdoll physics (section)

== Approaches ==
Ragdolls have been implemented using [[Featherstone's algorithm]] and spring-damper contacts.<ref>{{Cite patent|country=US|number=6067096|pubdate=2000-05-23|title=Method and system for generating realistic collisions in graphical simulations|inventor1-last=Nagle|inventor1-first=John}}</ref> An alternative approach uses constraint solvers and idealized contacts.<ref>{{cite conference|url=https://www.cs.cmu.edu/~baraff/sigcourse/|author1=Baraff, David  |author2=Witkin, Andrew |name-list-style=amp |title=Physically Based Modeling: Principles and Practice |conference=SIGGRAPH 97 | book-title=Proc. SIGGRAPH '97 |conference-url=http://www.siggraph.org/s97/| publisher=Association for Computing Machinery Special Interest Group on Graphics|year=1997| location=Los Angeles}}</ref>
While the constrained-rigid-body approach to ragdolls is the most common, other "[[pseudo]]-ragdoll" techniques have been used:

*[[Verlet integration]]: used by ''[[Hitman: Codename 47]]'' and popularized by [[Thomas Jakobsen]],<ref>{{cite web|url=http://www.teknikus.dk/tj/gdc2001.htm |title=Advanced Character Physics |publisher=Teknikus.dk |access-date=2008-11-30 |archive-url=https://web.archive.org/web/20080410171619/http://www.teknikus.dk/tj/gdc2001.htm|archive-date=April 10, 2008}}</ref>  this technique models each character bone as a point connected to an arbitrary number of other points via simple constraints. Verlet constraints are much simpler and faster to solve than most of those in a fully modelled rigid body system, resulting in much less CPU consumption for characters.
*[[Inverse kinematics]] post-processing: used in ''[[Halo: Combat Evolved]]'', this technique relies on playing a pre-set death animation and then using inverse kinematics to force the character into a possible position after the animation has completed. This means that, during an animation, a character could wind up [[Clipping (computer graphics)|clipping]] through world geometry, but after it has come to rest, all of its bones will be in valid space. Limitations can force body parts to move through each other in unnatural ways; for instance, a character's hand may lay on top of their chest in a death animation, but the hand is then moved through the chest to the ground underneath by inverse kinematics.
*Blended ragdoll: this technique was used in ''[[Halo 2]]'', ''[[Halo 3]]'', ''[[Call of Duty 4: Modern Warfare]]'', ''[[Left 4 Dead]]'', ''[[Medal of Honor: Airborne]]'', ''[[Team Fortress 2]]'', and ''[[Uncharted: Drake's Fortune]].'' It works by playing a pre-made animation, then binding the ragdoll to the last frame of the animation. Occasionally the ragdolling player model will appear to stretch out and spin around in multiple directions, as though the character were made of rubber. This erratic behavior has been observed to occur in games that use certain versions of the [[Havok (software)|Havok]] engine, such as ''Halo 2'' and ''[[Fable II]]''.
*Active ragdoll: used primarily in ''[[Unreal Engine]]'' games such as ''[[Unreal Tournament 3]]'' and ''[[Killing Floor 2]]''. It works by playing a pre-made animation, but constraining the output of that animation to what a physical system would allow. This helps alleviate the ragdoll feeling of characters suddenly going limp, offering correct environmental interaction as well. This requires both animation processing and physics processing, thus making it even slower than a traditional ragdoll alone, though the benefits of the extra visuals seem to overshadow the reduction in processing speed. See also: ''[[Euphoria (software)]]''
*[[Procedural animation]]: traditionally used in non-realtime media (film/TV/etc), this technique (used in the [[Medal of Honor (video game series)|Medal of Honor]] series starting from [[Medal of Honor: European Assault|European Assault]] onward) employs the use of multi-layered physical models in non-playing characters (bones / muscle / nervous systems), and deformable scenic elements from "simulated materials" in vehicles, etc. By removing the use of pre-made animation, each reaction seen by the player is unique, whilst still deterministic.