1. CS-378: Game Technology Lecture #15: Physically Based Simulation
Prof. Okan Arikan
University of Texas, Austin
Thanks to James O’Brien, Steve Chenney, Zoran Popovic, Jessica Hodgins V

2. Spring Mass Systems Masses connected by springs Can be used to model
Deformable objects
Cloth
Hair
Rigid bodies ?
Hitman

3. Spring Mass Systems Concrete example The state The forces
Position, velocity
The forces
Gravity, springs
The integration

4. Spring Mass Systems
Problems … ?
Tekken 5

5. Collisions Detecting collisions Broad phase Narrow phase
Find out intersecting bounding boxes
Sweep & prune
Narrow phase
Find out whether actual collision exists
Vertex/face, edge/face intersection tests

6. Collision Response
Push the colliding masses away

7. Collision Response Push the colliding masses away
Manually project the mass onto the surface
How can we handle friction ?

8. Collision Response Push the colliding masses away F
Apply a force proportional to the penetration depth
How can we handle friction ? F

9. Rigid Bodies Springs are not very good for rigid bodies
Why not ?
Abstract as meshes that don’t deform
Degrees of freedom ?
COM

10. Rigid Bodies Springs are not very good for rigid bodies
Why not ?
Abstract as meshes that don’t deform
Degrees of freedom ?
COM

11. Rigid Bodies Springs are not very good for rigid bodies
Why not ?
Abstract as meshes that don’t deform
Degrees of freedom ?
COM

12. Rigid Bodies Particles Position Velocity Equations Rigid Bodies
COM Position + Orientation
COM Velocity + Angular velocity