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Encyclopedia > Ragdoll physics
Early animation using ragdoll physics, from 1997.
Early animation using ragdoll physics, from 1997.

In computer physics engines, ragdoll physics are a type of procedural animation that is often used as a replacement for traditional static death animations. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A physics engine is a computer program that simulates Newtonian physics models, using variables such as mass, velocity, friction and wind resistance. ... A procedural animation is a method often used in computer and video games to automatically generate animation in real-time to allow for a more diverse series of actions than could otherwise be created by artists. ... The bouncing ball animation (below) consists of these 6 frames. ...

Contents

Introduction

Early video games used manually-created animations for characters' death sequences. This had the advantage of low CPU usage, as all that was needed to animate a "dying" character was chosen from a set number of pre-drawn animations. This article is about computer and video games. ... “CPU” redirects here. ...


As computers increased in power, it became possible to do limited real-time physical simulations. A ragdoll is therefore a collection of multiple rigid bodies (each of which is ordinarily tied to a bone in the graphics engine's skeletal animation system) tied together by a system of constraints that restrict how the bones may move relative to each other. When the character dies, his body begins to collapse to the ground, honouring these restrictions on each of the joints' motion, which often looks more realistic. Dynamical simulation, in computational physics, is the simulation of systems of objects that are free to move, usually in three dimensions according to Newtons laws of dynamics, or approximations thereto. ... In physics, a rigid body is an idealization of a solid body of finite size in which deformation is neglected. ... This article is about the skeletal organs. ... A technique in computer animation, particularly the animation of vertebrates, where a character is represented in two parts: a surface representation used to draw the character (called the skin) and a hierarchical set of bones used for animation only (called the skeleton). ... A constraint is a limitation of possibilities. ...


The term ragdoll comes from the problem that the articulated systems, due to the limits of the solvers used, tend to have little or zero joint/skeletal muscle stiffness, leading to a character collapsing much like a toy rag doll, often into comically improbable or compromising positions. This article or section does not cite any references or sources. ... A rag doll is a cloth doll, typically home-made from (and stuffed with) spare scraps of material. ...


The first game to exhibit ragdoll physics was the Jurassic Park licensed game Jurassic Park: Trespasser, which received very polar opinions; most were negative. The game had a large number of bugs but was remembered for being a pioneer in video-game physics engines. It has been suggested that Jurassic Park (computer game) be merged into this article or section. ...


Modern use of ragdoll physics goes beyond death sequences — there are fighting games where the player controls one part of the body of the fighter and the rest follows along, such as Rag Doll Kung Fu, and even racing games such as the FlatOut series. Screenshot of The King of Fighters XI (2005, SNK Playmore). ... Rag Doll Kung Fu is a fighting/party computer game created nearly entirely by the previous Lionhead Studios artist Mark Healey and distributed over Valves Steam content delivery platform starting October 12, 2005. ... FlatOut (a. ...


Approaches

Ragdolls have been implemented using Featherstone's algorithm and spring-damper contacts.[1] An alternative approach uses constraint solvers and idealized contacts.[2] While the constrained-rigid-body approach to ragdolls is the most common, other "pseudo-ragdoll" techniques have been used: Featherstones algorithm is a technique used for computing the effects of forces applied to a structure of joints and links (an open kinematic chain) such as a skeleton used in ragdoll physics. ... Pseudo is a prefix of Greek origin. ...

  • Verlet integration: used by Hitman: Codename 47 and popularized by Thomas Jakobsen [1], 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, 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 through world geometry, but after he has come to rest, all of his bones will be in valid space.
  • Blended ragdoll: this technique (used in Halo 2) 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, but offers correct environmental interaction as well. This requires both animation processing and physics processing, thus making it even slower than traditional ragdoll alone, though the benefits of the extra realism seems to overshadow the reduction in processing speed.

Verlet integration is a method for calculating the trajectories of particles in molecular dynamics simulations. ... 47 disguised. ... Inverse kinematics is the process of determining the movement of interconnected segments of a body or model. ... Halo is video game series created by Bungie Studios. ... In rendering, clipping refers to an optimization where the computer only draws things that might be visible to the viewer. ...

Ragdoll advantages/disadvantages

Due to the computationally expensive nature of performing simulations, most games using ragdolls use very simple approximations of characters:

  • Extremity bones such as fingers often go unsimulated.
  • Simple joints are used instead of actual constraints imposed by a true skeleton. (For example, human knee joints are often modelled as a rigid hinge even though an actual human knee allows some rotation.)
  • Simplified collision hulls are used to detect contact with other rigid bodies rather than detecting collision with the mesh.

The chief advantage ragdolls offer over traditional animations is that they allow much more correct interaction with the surrounding environment. Where it would be intractably time-consuming to try to hand-craft custom animations for all conceivable circumstances, ragdolls fill in and generate a reasonably accurate interpretation of events on the fly. This article does not cite any references or sources. ... For other uses, see Knee (disambiguation). ... A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. ... In computer gaming, a collision hull is an abstracted representation of the 3D world which the player can see. ... In relation to computer technology, on the fly describes activities that develop or occur dynamically rather than as the result of something that is statically predefined. ...


See also

Computer animation physics or game physics involves the introduction of the laws of physics into a simulation or game engine, particularly in 3D computer graphics, for the purpose of making the effects appear more real to the observer. ... A physics engine is a computer program that simulates Newtonian physics models, using variables such as mass, velocity, friction and wind resistance. ... A procedural animation is a method often used in computer and video games to automatically generate animation in real-time to allow for a more diverse series of actions than could otherwise be created by artists. ... Featherstones algorithm is a technique used for computing the effects of forces applied to a structure of joints and links (an open kinematic chain) such as a skeleton used in ragdoll physics. ... A rotational constraint on the joint of a bone system, used in an inverse_kinematics chain. ... Stair Dismount (also known as Porrasturvat) is a computer game made by Jetro Lauha. ...

References

  1. ^ US patent 6067096 "Method and system for generating realistic collisions in graphical simulations"
  2. ^ (1997) "Physically Based Modeling: Principles and Practice" in SIGGRAPH 97. Proc. SIGGRAPH '97, Los Angeles: Association for Computing Machinery Special Interest Group on Graphics. 

External links

Examples


  Results from FactBites:
 
Ragdoll Physics - Encyclopedia Dramatica (288 words)
Ragdoll Physics is the result of a gaming industry crisis that occurred about three years ago, during which developers began to realise "Oh shit!
Ragdoll Physics is the game engine innovation of the century.
Not to be confused with IRL physics, which does not cause those who die from gunfire to be propelled twenty feet into the air.
Ragdoll physics at AllExperts (817 words)
In computer game engines, ragdoll physics are a type of procedural animation that is often used as a replacement for traditional static death animations.
A ragdoll is therefore a collection of multiple rigid bodies (each of which is ordinarily tied to a bone in the graphics engine's skeletal animation system) tied together by a system of constraints that restrict how the bones may move relative to each other.
The term ragdoll comes from the fact that the articulated systems, due to the limits of the solvers used, tend to have little or zero joint/skeletal muscle stiffness, leading to a character collapsing much like a toy rag doll, often into an improbable and comedic position.
  More results at FactBites »

 
 

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