Character Animation in Games Appu Goundan Dhruv Thukral Yuting Ye - - PowerPoint PPT Presentation

Character Animation in Games

Appu Goundan Dhruv Thukral Yuting Ye

Combining and Morphing Motion Capture Data

 Limitations of Motion Capture

− Need to capture all motions of a character to able to

represent those actions on screen.

− Can create large databases that take up lots of space

and have large search times.

− Data from one character one accurate represent

another character of different dimensions.

− Requires large and expensive equipment to capture.

 Solutions : Morph and Combine data

− Use one small data base to create new motions

similar to the database based on external parameters

− Morph data from one capture session to match

anyone of any proportions and have that data look realistic.

− Capture all the data needed at once so that motion

capture doesn't have to be used again and then use modifications on that data base for everything, that way eliminating the need to return the motion capture aparatus.

Some Methods

 Motion Graphs  Motion Warping

Motion Graphs

 One database of motion capture data  Specify a requirement for the output motion

− A path to follow − A time to get from one point to another − A motion style

 Algorithm should choses small sections of data

and put them together to satisfy constraints and create satisfactory motion by interpolating end points of each section.

Motion Warping

 A (small) database of motions  Based on input :

− Location of key points in space − Certain obstacles in the way − Physical Constraints

 Create a motion :

− Similar to something in the database − Still realistic looking and physically plausible − Satisfies all the contraints.

 While it does make using motion capture data

more friendly, it has its limitations

 Created data is still somewhat close to motion

data, so something similar to the generated data has to be in the database.

 Sometimes the process is slow and can't be

generated in real time.

 Initial motion capture is still expensive.  Future ? : Model the human body so accurately

that expensive motion capture can be eliminated?

Adding Physics

Yuting Ye ANIMO Lab

Dynamics

• Lagragian equation
• d

dt T ˙ q T q Q = 0

tr(Wi q j Mi ˙ ˙ W

i T ) in( j)

• +

mig ci q j

in( j )

• +

Fk

k

• pk

q j + ks(q jq

j) + = 0

Forward Simulation

• Rigidbody simulation
• Ragdoll simulation
• NatualMotion Ltd (http://www.naturalmotion.com)
• Special controllers
• Gymnastics
• J. Hodgins, W. Wooten, D. Brogan, and J. O'Brien, Animating Human Athletics,

SIGGRAPH’95

• Balance Controller
• NaturalMotion Ltd

Simulation + Mocap

• Tracking
• Pollard, N., Zordan, V., Physically Based Grasping Control from Example, SCA’05
• Zordan, V., Hodgins, J., Motion capture-driven simulations that hit and react, SCA’02.
• Zordan, V., Hodgins, J., Tracking and Modifying Upper-body Human Motion Data

with Dynamic Simulation, Computer Animation and Simulation '99

• Blending Mocap to Simulation
• Dynamic response
• Zordan, V. et al, Dynamic Response for Motion Capture Animation, SIGGRAPH’05
• Endorphin
• NaturalMotion Ltd

Pros and Cons

• Pros
• Interactive
• Realtime
• Cons
• Hard to design
• Too specific

Spacetime Optimization

• Luxo Jr.
• A. Witkin and M. Kass., Spacetime constraints, SIGGRAPH’88

Spacetime + Mocap

• From poses
• Liu, C. K. and Popović, Z. Synthesis of Complex Dynamic Character Motion

from Simple Animation, SIGGRAPH’02

• From simple clips
• Abe, Y., Liu, C. K., and Popović, Z. Momentum-based Parameterization of

Dynamic Character Motion, SCA’04

• Multiple characters interactions
• Liu, C. K., Hertzmann, A., Popovic, Z. Composition of Complex Optimal

Multi-Character Motions, SCA’06

Inverse Optimization

• Learning style from motion
• Liu, C. K., Hertzmann, A. and Popović, Z. Learning Physics-based Motion Style

with Nonlinear Inverse Optimization, SIGGRAPH’05

Pros and Cons

• Pros
• Realistic (v.s. robotic)
• Anticipation and follow through
• Full user control
• Cons
• Computationally expensive
• No user interaction

Optimization-based Forward Simulation

• Sumit Jain, Yuting Ye, C. Karen Liu, Optimization-based

Interactive Character Simulation, under review

Pros and Cons

• Pros
• Interactive
• High level control
• Realistic
• Easy to design
• Versatile
• Cons
• Not realtime
• No planning

Importing Motion Capture Data into Gaming

Dhruv Thukral Gamepipe Labs

High Level Process

 Go to Yuting and ask her for the .C3D Motion Capture Sessions.  Export a character skeleton (Maya) to use in Motionbuilder.  Import the MoCap data and skeleton into Motionbuilder and

apply them to a Motionbuilder Actor.

 Create a resulting Motion Builder Character and apply all the

animations to it.

 Export the resulting character to use in Maya.  Make optimizations in Maya and export the character in a game

engine specific format.

 Use the character in your games.

Export Maya Skeleton to MotionBuilder FBX format

Import to Motion Builder

We then associate a character with the imported skeleton and in this case we will characterize it as a Biped

Create an actor and associate with Mocap Data

Map actor to optical data

Map actor to optical data



In the screenshot you see a 2D version of the actor model with numbers within circles. This is the number of optical markers that have been assigned to the bone over which the circle lies.



This will let you set the optical markers from the .c3d mocap data to influence bones in your Actor.

Voila Look what we have!

Export the file

Import into Maya and Optimize

Export into game engines and..

and