The document discusses physics and dynamics in 3D computer animation and games. It describes how computer animation physics involves introducing laws of physics into game engines to make effects appear more realistic. There are two main types of physics simulations: rigid body, where objects interact in predefined categories, and soft-body, where individual sections of objects behave more realistically. The document also provides examples of how physics is used for rigid bodies, soft bodies, and particle systems like explosions in games.

1. Physics and Dynamics
3D Animation & Realism
COMPUTER GAMES
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2. Basic information
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.
Typically, simulation physics is only a close approximation to real physics, and
computation is performed using discrete values.
There are two central types of physics simulations; rigid body and soft-body
simulators. In a rigid body simulation objects are grouped into categories based
on how they should interact and are less performance intensive. Soft-body
physics involves simulating individual sections of each object such that it behaves
in a more realistic way.
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3. There has been a tendency, especially within big Triple A rated games, to make 3D Animation
more realistic. With advancements in physics engines coupled with Motion Capture are now the
go to tool in the industry for making realistic & believable human behaviour in games. However,
it was a long process to get to the stage we are at now, now being the “Next-Gen” stage. There
are still some problems or “Limitations” that still occur with the use of Motion Capture systems.
3D Animation
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4. Problems with Body Motion Capture
For the most part Motion Capture has the ability to capture actual movement, through use of
body actors and body suits, very well. However, there are just a few disadvantages that
come with that. Whilst having realistic motion is always a bonus, its now made it even
harder to use in games, as games at their very nature are not meant to be real.
The article below states that it is tricky to combine & adapt to certain situations. Such as
environmental factors, questions about how does realistic action fit within computer
generated worlds need to be raised. Major games that use this are games such as GTA 5,
WATCH DOGS & ASSASSINS CREED. What these all have in common is that the realistic
motion works because of the very realistic environments, be it modern day or historic are all
man made, thus fitting and working well with Motion capture. However, what if the world
the game was set in was not contemporary or even Earth. How would they transfer over
then?
http://www.cs.jhu.edu/~cohen/RendTech99/Lectures/Computer_Animation.color.pdf
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5. http://en.wikipedia.org/wiki/Motion_capture
According to the wikipedia entry above, movements that do not follow the natural law of physics
cannot be captured in Motion capture technology. This provides problems for when a captured
sequence needs to have added to It, an un-natural movement.
The clip features an ability you
can perform in the game
Assassins Creed : Revelations, a
movement called a hook and
run, where you can use Enzio's
hidden blade to hook over an
opponent to escape. Watch the
jarring action between the
natural running motion,
captured with Motion Capture,
and the un- natural Hook and
run, which was created using
animation you can clearly see a
difference.
Problems with Body Motion Capture
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6. Problems with Body Motion Capture
http://www.techradar.com/news/gaming/motion-capture-is-the-death-of-half-life-3-alleges-voice-
actor-john-patrick-lowrie-1173697
The magazine article above raises some other issues with Motion Capture technology in relation
to the the game Half Life 3. The Half Life series is meant to give players the freedom of
controlling the direction of the plot and storyline. Whilst you will all meet at the same ending,
decisions taken by players may affect the progression of the story of the game. That makes us
part of the problem in that making the gameplay based on motion captured actors, instead of
using animation to create the different possibilities in which the player can control a character,
motion capture means you are simply limited to that was captured in Motion Capture process.
This makes for an extremely ambitious game.
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7. Problems with Facial Motion Capture
Despite the challenges listed in the previous section,body motion capture has made far more
significant strides than facial motion capture.
The resolution and detail required to create accurate expressions & facial features are far
greater than those needed for body motion capture.
http://www.develop-online.net/tools-and-tech/motion-capture-moving-with-the-times/0117523
In the article above it states, “The real challenge according to Mick Morris, MD of mo-cap
service provider AudioMotion, however, is a matter staring the industry in the face. The
human face is, of course, the most expressive part of our body, and at the very centre of
almost any performance. Captured incorrectly, it can let an entire game down, and it is still
tough for mo-cap solutions to grasp the essence of.”
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8. Facial Motion Capture
As you will see in the video link below, the character animators for the big Triple A game 'The
Last of Us' developed by Naughty Dog studios, use the facial expressions, performed by the
body actors, as a guide but not as the piece they edit. They create the facial features from
scratch. The animators said they get to create far greater detail by adding features and
expression manually frame by frame. So like with anything, it has its drawbacks. However,
Motion Capture is by far the way forward for animation in video games.
http://youtu.be/R0l7LzC_h8I
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9. More Examples of Physics and Dynamics
RIGID-BODY
Rigid-body dynamics studies the movement of systems of
interconnected bodies under the action of external forces. The
assumption that the bodies are rigid, which means that they do not
deform under the action of applied forces, simplifies the analysis
by reducing the parameters that describe the configuration of the
system to the translation and rotation of reference frames attached
to each body.
SOFT-BODY
The applications are mostly in video games and film. Unlike in
simulation of rigid bodies, the shape of soft bodies can change,
meaning that the relative distance of two points on the object is not
fixed. While the relative distances of points are not fixed, the body
is expected to retain its shape to some degree, unlike a fluid.
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10. RIGID-BODY SOFT-BODY
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11. PARTICLE SYSTEMS
A common aspect of computer games that model some type of conflict is the explosion. Early
computer games used the simple expedient of repeating the same explosion in each
circumstance. However, in the real world an explosion can vary depending on the terrain,
altitude of the explosion, and the type of solid bodies being impacted. Depending on the
processing power available, the effects of the explosion can be modelled as the split and
shattered components propelled by the expanding gas. This is modelled by means of a
particle system simulation. A particle system model allows a variety of other physical
phenomena to be simulated, including smoke, moving water, precipitation, and so forth. The
individual particles within the system are modelled using the other elements of the physics
simulation rules, with the limitation that the number of particles that can be simulated is
restricted by the computing power of the hardware. Thus explosions may need to be
modelled as a small set of large particles, rather than the more accurate huge number of
fine particles.
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12. Examples In Gameplay
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