1. Physics in Games David: Overview of Physics in Games
Steven: Character Animation
Ryan: Effects
Dan: Development Applications
Lowell: How physics engines work, future of physics *

2. Tennis for Two (1958) First video game to incorporate physics
Used ballistic missile calculations to simulate a tennis ball

3. Spacewar! (1962) Used velocity calculations for ship movement
First use of gravity simulation in a gravity well

4. Pong (1972) First commercially successful video game
Used basic calculations for deflection and collision

5. Super Mario Bros. (1985)
Incorporated acceleration, friction, and momentum into player movement

6. Jurassic Park: Trespasser (1998)
First game world completely controlled by classical mechanics
First game to use ragdoll physics

7. Havok Physics (2000) Commercial physics engine Collision detection
Rigid bodies
Multibody systems
Ragdoll physics
Animation
Inverse kinematics

8. PhysX (2004) Developed by Ageia Acquired by Nvidia in 2009
Collison detection
Joints
Materials
Ragdoll
Volumetric fluid
Cloth

9. Most Popular Physics Engines of 2009

10. Red Faction (2001) Features Geo Mod engine
Allowed for destructible environments

11. Half Life 2 (2004)
Uses Havok Physics
Made use of gravity gun

12. Assassin’s Creed (2007) Features heavy use of inverse kinematics
Allows for Parkour / Freerunning

13. Arkham Asylum (2009) Hardware-accelerated PhysX support
Dynamic fog and steam
Cloth physics
Spark effects

14. From Dust (2011)
Use of fluid dynamics to model sand, dust, lava, and water

15. Crysis 3 (2013) Soft particle system Parametric skeletal animation
Multi-threaded physics engine
Soft body physics
Destructible environments
Rope physics

16. Character Animation Forward Kinematics Inverse Kinematics
Ragdoll Physics

17. Forward Kinematics An Example Rotation of base: Rb
Apply M = Rb to base
Translate lower arm relative to base: Tla
Rotate lower arm around joint: Rla
Apply M = Rb Tla Rla to lower arm
Translate upper arm relative to upper arm: Tua
Rotate upper arm around joint: Rua
Apply M = Rb Tla Rla Tua Rua to upper arm

18. Forward Kinematics The Problem
Moving something high in hierarchy moves its children

19. Inverse Kinematics Bottom-up approach More fluid and realistic motion
More intuitive
Higher computation cost

20. Inverse Kinematics Implementations Jacobian Solutions
Jacobian Transpose, Jacobian Pseudoinverse, Damped Least Square
Rely on Jacobian Matrix
Sometimes unstable and fail to converge
Cyclic-Coordinate Descent
Optimization Solution
Simpler to understand and easy to process
Loop joints from tip to root trying to get them as close to target as possible

21. Ragdoll Physics Problem:
Canned death animations repetitive, boring, and unrealistic
Solution:
Ragdoll Physics

22. Ragdoll Physics Implementations Verlet Integration
Series of bones connected at points with simple constraints
Inverse Kinematics Post-Processing
Play an animation; use IK thereafter
Blended Ragdoll
Play an animation, but constrain during playback
Procedural Animation
Agents make decisions that translate to unique movements in real time

23. Ragdoll Physics

24. Particle Systems
A technique that uses many small sprites or objects to simulate "fuzzy" phenomena, such as fire, smoke, moving water, etc.
Two main types of particle systems
Animated Particle Systems
Static Particle Systems

25. Animated Particle Systems
Specific points in each particle's life cycle are rendered each frame.
Particles may have a fade out time or limited life span.
This type of particle system is used to animate effects like fire and precipitation.

26. Static Particle Systems
The entire life cycle of each particle is rendered simultaneously in each frame.
Rather that point particles, we have the particle's overall trajectory.
This type of particle system is used to animate effects like hair and grass.

27. How Particle Systems Work
A particle system is usually controlled by an emitter.
The emitter acts as the source of the particles, i.e. where the particles are generated and where they go.
Each emitter has a set of parameters that can be adjusted to change the behaviour and rendering of the particles.
Particle life span
Particle color / texture
Forces acting upon the particles

28. How Particle Systems Work (cont.)
Animation is done in two stages:
Simulation Stage
Here, new particles that need to be created are calculated based on spawn rates, time intervals, etc.
Existing particles have their positions updated or are removed if the end of their life span has been reached.
Rendering Stage
Here, each particle is rendered according to the calculations done in the previous stage.

29. Particle Systems Next Time
Look at some algorithms used in particle systems
Show a few demos

30. Physics in Development Applications -Dan*

31. Unity Primarily uses PhysX, engine developed by Nvidia.
Effects include:
Cloth:
Interactive
Skinned *

32. Unity Soft Bodies Rigid Bodies
Deformable objects, distances between vertices are not fixed. Limited documentation.
Rigid Bodies
Objects can receive force, torque, gravity, etc.
Main way to apply collisions
Supports special colliders such as the “Wheel Collider” *

33. Unity Character rigging:
Supports hinge joints, ball-sockets, character limbs.
Ragdoll physics can be enabled through Unity’s premade wizard and applied to Skinned Meshes. *

34. Blender
Open-source 3D graphics software. Supports modeling, animation, rendering, and some game- engine functions.
Supports a plethora of physics engines. *

35. Blender Bullet Physics:
Directly integrated into Blender. Allows for rigid body simulations.
Scripts usually controlled through Python
Simulations are typically baked *

36. Blender Phymec: Built off of Bullet engine.
UI tools for Blender still in development.
Example of Voronoi Shattering *

37. XNA JellyPhysics by Walaber 2D soft-bodied physics system.
Follows collision of vertices, changes between concave and convex forms.
JelloCar! *

38. Next Week
How 3rd party engines such as Farseer Physics can work in Unity and XNA
Go through brief demo of KEVA engine in Blender *

39. How Physics Engines Work
Simulate Physics Calculations
Position, velocity, acceleration, rotation, etc.
Real-Time
Computed every frame in real time
Used in games
Low precision, only computes what is necessary
High-Precision
Not real time
Typically used by scientists, animators

40. Optimizing Physics for Games
Rigid Body Dynamics
Faster, easier to calculate
Brownian Motion
Objects outside of scope or at rest on a surface are put to sleep

41. Collision Detection/Response System
Detect collisions and send trigger to system
Volumetric Tessellation
Simplify 3D meshes by surrounding them with more simple tessellated meshes

42. Collision Detection
Works by detecting the moment two or more bodies collide and then applies the correct respective forces

43. Discrete Collision Detection
Predicts the trajectory of the body after the actual collision when meshes are intertwined
Causes problems in “fixing step”, bodies may pass through another
Continuous Collision Detection
Predicts the trajectory of the body before the actual collision

44. Bounding Box Approximation
An enlarged box surrounding current and last position
When these boxes collide, the engine will have an approximation for a collision
Cheaper than mesh collision

45. Where are Physics engines headed now?
The main limiting factor is the precision and complexity of calculations
Faster computer and graphics processors allow games to push the engines further and do more complex simulations
Balance precision of calculations with a “perceptually correct” approximation

46. New Physics Effects Soft Body Dynamics Complex Particle Effects
Realistic Fluid Dynamics
Real Time Fracturing