Physics and Dynamics in Video Games

3D Animation & Realism

What are Video

Game Physics?

• Computer animation physics or video

game physics is the implementation of

the laws of physics into a simulated

game engine. Physics engines are

particularly used in 3D video games for

the purpose of making the game more

realistic. Physics engines are very

complex and are still being improved

on as physics in video game has still

not reached a completely “realistic”

point. There are two main types of

physics simulation; rigid body and soft

body simulators. Rigid body are

simulation objects grouped into

categories based on how they should

interact and are less performance

intensive. Soft-body physics allows for

object to deform, or change shape,

allowing for more realistic outcomes

but at the expense of more processing

power needed.

Rigid Body and Soft Body

Rigid Body Soft Body

3D Animation

• 3D animation in games has

improved dramatically since it’s

first arrival in DooM, the first real

3D video game back in 1993,

however game developers are

still striving to improve 3D

animation technology to create

the most realistic games

possible. With advancements in

physics engines coupled with

motion capture, video game

developers have been able to

create more realistic virtual

environments as well as realistic

character movements. There are

however still limitations in 3D

animation that still need to be

overcome.

Problems with Body Motion Capture

Body Motion Capture

Body Motion capture revolutionised video game

character movement through the use of real life

actors and body suits that would track the actors

movement, implementing them onto a character in a

game.

Although realistic character movements using

motion capture may seem to be the best way to

create realistic movements, but that isn't the case.

Using body motion capture limits the game

character, as for a completely realistic character

movement, a character must move differently

depending on changes in its virtual environment. For

example, You could body motion capture an actor

climbing up a wall and then use it in the game, which

would then climb up walls exactly like that each time.

However, realistically a person would climb up a wall

slightly differently every time.

Body Motion Capture

An article I read (check reference slide) suggests it

is tricky to combine and adapt body motion capture

to certain situations such as environmental factors.

The article reads that the realistic motion from body

motion capture works because of the very realistic

environments it works in, but questions how body

motion capture could be used in a game whose

environment is not contemporary, or even planet

earth with different physics.

Body Motion Capture

Another problem with body motion capture is

movements that do not follow the natural law of

physics cannot be captured with motion capture

technology, meaning those movements need to be

animated, which can look very strange added with

realistic movement. Fore example, in the game

Assassin’s Creed: Revelations, a movement

sequence called the “hook and run” allows the

player to hook over an opponents head when

running to avoid the opponent. As this movement is

not possible to capture using body motion capture, it

needed to be animated separately and then added

with the motion captured running movement. This

gave the whole action of the “hook and run” an

unrealistic, unnatural look.

Facial Motion Capture

Facial Motion Capture has even more problems

however than body motion capture. As video games

become more realistic due to the advancements in

graphics, AI and 3D animation, it is increasingly

important to have realistic facial expressions. As the

human face can express so much, more than the

rest of the body, games which aim to show realism

rely on facial expressions to portray the character’s

emotions. An article I have read addresses this issue

and states that if facial motion is captured incorrectly

“it can let an entire game down, and it is still tough

for mo-cap solutions to grasp the essence of”.

Facial Motion Capture

In the video game The Last Of Us, Naughty Dog, the

developers of the game, used the facial expressions,

performed by the body actors, as a guide but not as

the finished result. They created the facial

expressions from scratch. The animators have said

they get to create far greater detail by adding

features and expressions manually, frame by frame.

This shows that facial motion capture still has a long

way to go, although it has helped create a basis for

facial expression animation.

Particle Systems

Particle Systems

Explosions in computer games can be hard to

implement. Video game developers use particle

systems to recreate the effects of the propelled gas

and shrapnel caused by explosions. A particle

system allows for a variety of other physical actions

caused by particles to be simulated, such as smoke,

moving water, rain etc. 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.

This means that games tend to model explosions as

a small set of large particles, instead of a large

number of small particle, to be able to work on the

majority of computer systems.

References

• (Body Motion Capture)

http://www.cs.jhu.edu/cohen/RendTech99/Lectures/Computer_Animation.color.pdf

• (Motion Capture) http://en.wikipedia.org/wiki/Motion_capture

• (Facial Motion Capture) http://www.develop-online.net/tools-and-tech/motion-

capture-moving-with-the-times/0117523

• (Naughty Dog Facial Expressions) http://www.youtube.com/watch?v=R0l7LzC_h8I

• (Particle Systems) http://en.wikipedia.org/wiki/Particle_system