Ragdoll physics
Encyclopedia
Physics engine
A physics engine is computer software that provides an approximate simulation of certain physical systems, such as rigid body dynamics , soft body dynamics, and fluid dynamics, of use in the domains of computer graphics, video games and film. Their main uses are in video games , in which case the...
s, ragdoll physics is a type of procedural animation
Procedural animation
A procedural animation is a type of computer animation, used to automatically generate animation in real-time to allow for a more diverse series of actions than could otherwise be created using predefined animations....
that is often used as a replacement for traditional static death animation
Animation
Animation is the rapid display of a sequence of images of 2-D or 3-D artwork or model positions in order to create an illusion of movement. The effect is an optical illusion of motion due to the phenomenon of persistence of vision, and can be created and demonstrated in several ways...
s.
Introduction
Early video games used manually-created animations for characters' death sequences. This had the advantage of low CPUCentral processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
utilization as the data needed to animate a "dying" character was chosen from a set number of pre-drawn frames. 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
Rigid body
In physics, a rigid body is an idealization of a solid body of finite size in which deformation is neglected. In other words, the distance between any two given points of a rigid body remains constant in time regardless of external forces exerted on it...
(each of which is ordinarily tied to a bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
in the graphics engine's skeletal animation
Skeletal animation
Skeletal animation is a technique in computer animation in which a character is represented in two parts: a surface representation used to draw the character and a hierarchical set of interconnected bones used to animate the mesh...
system) tied together by a system of constraints that restrict how the bones may move relative to each other. When the character dies, their body begins to collapse to the ground, honouring these restrictions on each of the joints' motion, which often looks more realistic.
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
Skeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
stiffness, leading to a character collapsing much like a toy rag doll
Rag doll
A rag doll is a children's toy. It is a cloth figure, a doll traditionally home-made from spare scraps of material. They are one of the most ancient children's toys in existence; the British Museum has a Roman rag doll, found in a child's grave dating from 300 BC.Rag dolls have featured in a...
, often into comically improbable or compromising positions.
The first game to exhibit ragdoll physics was the Jurassic Park
Jurassic Park (franchise)
The Jurassic Park franchise is a series of books, films, comics, and videos centering on a disastrous attempt to create a theme park of cloned dinosaurs...
licensed game Jurassic Park: Trespasser
Jurassic Park: Trespasser
Jurassic Park: Trespasser is a video game released in 1998 for Microsoft Windows after much hype and anticipation. The player assumes the role of Anne, the sole survivor of a plane crash on InGen's "Site B" one year after the events of The Lost World: Jurassic Park...
, which received very polarised opinions; most were negative, as the game had a large number of bugs. It was remembered, however, for being a pioneer in video game physics.
Modern use of ragdoll physics goes beyond death sequences—there are fighting game
Fighting game
Fighting game is a video game genre where the player controls an on-screen character and engages in close combat with an opponent. These characters tend to be of equal power and fight matches consisting of several rounds, which take place in an arena. Players must master techniques such as...
s where the player controls one part of the body of the fighter and the rest follows along, such as Rag Doll Kung Fu
Rag Doll Kung Fu
Rag Doll Kung Fu is a fighting computer game, created predominantly by artist Mark Healey, while working for Lionhead Studios, along with other Lionhead employees, such as David Smith and Alex Evans. Rag Doll Kung Fu is available from Valve's Steam content delivery platform...
, and even racing games such as the FlatOut
FlatOut
FlatOut is a racing video game developed by Finnish Bugbear Entertainment and published by Empire Interactive and Vivendi Universal Games in 2004 and 2005. Gameplay in Flatout places emphasis on demolition derby-style races, and features a sophisticated physics engine...
series.
Recent procedural animation
Procedural animation
A procedural animation is a type of computer animation, used to automatically generate animation in real-time to allow for a more diverse series of actions than could otherwise be created using predefined animations....
technologies, such as those found in NaturalMotion
NaturalMotion
NaturalMotion is a software company with offices in Oxford and San Francisco. Founded in November 2001 as a spin-off of Oxford University, the company specialises in creating animation technology for the game and film industries.-Technology:...
's Euphoria
Euphoria (software)
Euphoria is a game animation engine created by NaturalMotion based on Dynamic Motion Synthesis, NaturalMotion's proprietary technology for animating 3D characters on-the-fly "based on a full simulation of the 3D character, including body, muscles and motor nervous system"...
software, have allowed the development of games that rely heavily on the suspension of disbelief
Suspension of disbelief
Suspension of disbelief or "willing suspension of disbelief" is a formula for justifying the use of fantastic or non-realistic elements in literary works of fiction...
facilitated by realistic whole-body muscle/nervous ragdoll physics as an integral part of the immersive gaming experience, as opposed to the antiquated use of canned-animation techniques. This is seen in Grand Theft Auto IV
Grand Theft Auto IV
Grand Theft Auto IV is a 2008 open world action video game published by Rockstar Games, and developed by British games developer Rockstar North. It has been released for the PlayStation 3 and Xbox 360 video game consoles, and for the Windows operating system...
, as well as titles such as LucasArts
LucasArts
LucasArts Entertainment Company, LLC is an American video game developer and publisher. The company was once famous for its innovative line of graphic adventure games, the critical and commercial success of which peaked in the mid 1990s...
' Star Wars: The Force Unleashed
Star Wars: The Force Unleashed
Star Wars: The Force Unleashed is a multimedia project developed by LucasArts along with Dark Horse Comics, Lego, Hasbro, and Del Rey Books...
and Red Dead Redemption.
Approaches
Ragdolls have been implemented using Featherstone's algorithmFeatherstone's algorithm
Featherstone's algorithm is a technique used for computing the effects of forces applied to a structure of joints and links such as a skeleton used in ragdoll physics....
and spring-damper contacts. An alternative approach uses constraint solvers and idealized contacts.
While the constrained-rigid-body approach to ragdolls is the most common, other "pseudo
Pseudo
The prefix pseudo- is used to mark something as false, fraudulent, or pretending to be something it is not.-See also:*Falsehood*Pseudorealism*Deception*Mimicry*Pseudo.com*Pseudo: Blood of Our Own...
-ragdoll" techniques have been used:
- Verlet integrationVerlet integrationVerlet integration is a numerical method used to integrate Newton's equations of motion. It is frequently used to calculate trajectories of particles in molecular dynamics simulations and computer graphics...
: used by Hitman: Codename 47Hitman: Codename 47Hitman: Codename 47 is a stealth game developed by IO Interactive and published by Eidos Interactive. It is the first entry in the Hitman series, followed by Hitman 2: Silent Assassin....
and popularized by Thomas JakobsenThomas JakobsenThomas Jakobsen is a mathematician, cryptographer, and computer programmer, formerly anassistant professor at the Technical University of Denmark and head of research anddevelopment at IO Interactive...
, 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 kinematicsInverse kinematicsInverse kinematics is a subdomain of kinematics, which is of particular interest in robotics and computer animation. In contrast to forward kinematics, which calculates the position of a body after a series of motions, inverse kinematics calculates the motions necessary to achieve a desired...
post-processing: used in Halo: Combat EvolvedHalo: Combat EvolvedHalo: Combat Evolved, frequently referred to as Halo: CE, or Halo 1, is a first-person shooter video game developed by Bungie and published by Microsoft Game Studios. The first game of the Halo franchise, it was released on November 15, 2001 as a launch title for the Xbox gaming system, and is...
and Half-Life 1, 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 clippingClipping (computer graphics)Any procedure which identifies that portion of a picture which is either inside or outside a picture is referred to as a clipping algorithm or clipping.The region against which an object is to be clipped is called clipping window.-Examples:...
through world geometry, but after it has come to rest, all of its bones will be in valid space.
- Blended ragdoll: this technique was used in Halo 2Halo 2Halo 2 is a first-person shooter video game developed by Bungie Studios. Released for the Xbox video game console on November 9, 2004, the game is the second installment in the Halo franchise and the sequel to 2001's critically acclaimed Halo: Combat Evolved...
, Halo 3Halo 3Halo 3 is a first-person shooter video game developed by Bungie for the Xbox 360 console. The third installment in the Halo franchise, the game concludes the story arc begun in Halo: Combat Evolved and continued in Halo 2...
, Call of Duty 4: Modern WarfareCall of Duty 4: Modern WarfareCall of Duty 4: Modern Warfare is a 2007 first-person shooter video game, developed by Infinity Ward and published by Activision for Microsoft Windows, Mac OS X, PlayStation 3, Xbox 360 and Wii. A handheld game was made for the Nintendo DS. The game was released in North America, Australia, and...
, Left 4 DeadLeft 4 DeadLeft 4 Dead is a cooperative first-person shooter video game. It was developed by Turtle Rock Studios, which was purchased by Valve Corporation during development. The game uses Valve's proprietary Source engine, and is available for Microsoft Windows, Xbox 360 and Mac OS X...
, Medal of Honor: AirborneMedal of Honor: AirborneMedal of Honor: Airborne is a World War II first-person shooter computer game and the 11th installment of the Medal of Honor series. It was developed by EA Los Angeles and was released worldwide on the PC and Xbox 360 in September 2007. A PS2 and Wii version was set to be released but was cancelled...
, and Uncharted: Drake's Fortune. 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 traditional ragdoll alone, though the benefits of the extra realism seem to overshadow the reduction in processing speed. 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 HavokHavok (software)Havok Physics is a physics engine developed by Irish company Havok. It is designed primarily for video games, and allows for real-time collision and dynamics of rigid bodies in three dimensions. It provides multiple types of dynamic constraints between rigid bodies , and has a highly optimized...
engine, such as Halo 2 and Fable II.
- Procedural animationProcedural animationA procedural animation is a type of computer animation, used to automatically generate animation in real-time to allow for a more diverse series of actions than could otherwise be created using predefined animations....
: traditionally used in non-realtime media (film/TV/etc), this technique (used in the Medal of HonorMedal of Honor (series)Medal of Honor is the name of a series of first-person shooter games set in World War II, with an October 2010 reboot based on the conflicts of present day Afghanistan. The first game was developed by DreamWorks Interactive and published by Electronic Arts in 1999 for the PlayStation game console...
series starting from European AssaultMedal of Honor: European AssaultMedal of Honor: European Assault is the 6th installment in the long running Medal of Honor series. European Assault was released for PlayStation 2, Xbox and GameCube in June 2005. The game's story was written by John Milius, the writer of Apocalypse Now...
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. Rather than detract from gameplay through overstimulation, the "natural" qualities of movement provide for a more immersive experience, and extended replayability.
See also
- Cartoon physicsCartoon physicsCartoon physics is a jocular system of laws of physics that supersedes the normal laws, used in animation for humorous effect. Normal physical laws are referential , but cartoon physics are preferential ....
- Game physicsGame physicsComputer 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...
- Physics enginePhysics engineA physics engine is computer software that provides an approximate simulation of certain physical systems, such as rigid body dynamics , soft body dynamics, and fluid dynamics, of use in the domains of computer graphics, video games and film. Their main uses are in video games , in which case the...
- Procedural animationProcedural animationA procedural animation is a type of computer animation, used to automatically generate animation in real-time to allow for a more diverse series of actions than could otherwise be created using predefined animations....
- Featherstone's algorithmFeatherstone's algorithmFeatherstone's algorithm is a technique used for computing the effects of forces applied to a structure of joints and links such as a skeleton used in ragdoll physics....
- Joint constraintsJoint constraintsJoint constraints are rotational constraints on the joints of an artificial bone system. They are used in an inverse kinematics chain, for such things as 3D animation or robotics. Joint constraints can be implemented in a number of ways, but the most common method is to limit rotation about the X,...
- Stair DismountStair DismountStair Dismount is a computer game originally made by Jetro Lauha of tAAt. It is a puzzle game where the goal is maximising the 'damage' done to a 3D stickman figure; the player causes damage by applying a force to the figure to make it fall down a staircase.The stick figure's falls are...
- Euphoria EngineEuphoria (software)Euphoria is a game animation engine created by NaturalMotion based on Dynamic Motion Synthesis, NaturalMotion's proprietary technology for animating 3D characters on-the-fly "based on a full simulation of the 3D character, including body, muscles and motor nervous system"...
- Truck DismountTruck DismountTruck Dismount is a computer game made by Jetro Lauha of tAAt. Truck Dismount is a simple stress-reliever, allowing players to release their anger on a 3D stick figure....
- lugaruLugaruLugaru: The Rabbit's Foot is the first commercial video game created by Wolfire Games. It is a cross-platform, 3D action game for Microsoft Windows, Mac OS X, and GNU/Linux. It features Turner, an anthropomorphic rabbit with curiously well-developed combat skills.Lugaru was made almost solely by...
External links
- GDC 2001 Proceedings Archive Archived version of Advanced Character Physics
- Ragdoll Games
Examples
- Ragdoll Games A collection of Ragdoll games online, made using Flash
- Grand Theft Auto IV uses procedural animation middleware throughout.
- Rag Doll Kung Fu
- Ragdoll Masters, a fighting game with ragdolls (sharewareSharewareThe term shareware is a proprietary software that is provided to users without payment on a trial basis and is often limited by any combination of functionality, availability, or convenience. Shareware is often offered as a download from an Internet website or as a compact disc included with a...
download) - Ski stunt simulator (java)
- Falling woman (flash)
- Thomas Jakobsen's article about the integration of Verlet
- Half-life 2 The sequel of Valve's best winning game, Half-life, using the Source engineSource engineSource is a 3D game engine developed by Valve Corporation. It debuted in June 2004 with Counter-Strike: Source and shortly thereafter Half-Life 2, and has been in active development ever since...
.
Physics
- Stair DismountStair DismountStair Dismount is a computer game originally made by Jetro Lauha of tAAt. It is a puzzle game where the goal is maximising the 'damage' done to a 3D stickman figure; the player causes damage by applying a force to the figure to make it fall down a staircase.The stick figure's falls are...
and Truck DismountTruck DismountTruck Dismount is a computer game made by Jetro Lauha of tAAt. Truck Dismount is a simple stress-reliever, allowing players to release their anger on a 3D stick figure.... - Sumotori Dreams
- Toribash
- Online Boxing 3D a game that uses ragdoll physics to simulate boxing matches played over the internet
- Trials HD