1. Physics in Games David: Achieving Fun with Physics
Steven: Ronin Game Engine
Ryan: Fire and Explosion Effects
Dan: Farseer and Bullet Physics
Lowell: Physics in Unity; Forcemode Demo *

2. Richer Graphical Environment
Batman: Arkham Asylum
Uses PhysX for enhanced graphical effects
Simulates colliding particles, smoke, cloth
Graphical fidelity requires physical fidelity

3. Richer Physical Environment
Half Life 2
Havok Engine provides a game environment where objects become part of gameplay
Conforms to player expectations of a physical environment

4. Realism Grand Theft Auto IV
Uses Rockstar Advanced Game Engine with Euphoria
Most realistic vehicle handling of the series
Players can be ejected through a windshield
Maneuvering a vehicle requires skill
Forces the player to consider consequences

5. Lack of Realism Just Cause 2 Uses Havok physics
Parameters like friction and momentum are adjusted for behavior conducive to gameplay, not realism
Emphasis on lack of consequence, escapism

6. Emergent Gameplay Crayon Physics Deluxe
Uses Box2D, an open source 2D physics engine
Players must guide a ball to touch all stars in a level
Draw rigid surfaces, pivots, wheels, and ropes
Simple physical interactions lead to complex solutions

7. Character Animation Review
Forward Kinematics
Inverse Kinematics
Ragdoll Physics

8. Ronin Game Engine Developed by LucasArts Medley of Individual Engines
Havok - Havok
Digital Molecular Matter (DMM) - Pixelux Entertainment
Euphoria - NaturalMotion

9. Havok Staple physics engine for LucasArts Provides functionality for:
Rigid Body Physics
Collision Handling
Ragdoll Physics

10. Digital Molecular Matter (DMM)
Define properties of deformable objects
Properties such as:
Young’s Modulus (measure of a material’s stiffness)
Poisson’s Ratio (measure of “volume preservation”)
Able to simulate many different materials with very different properties
Steel
Glass
Wood

11. Euphoria Advanced AI behavior Never same scenario twice
Uses Inverse Kinematics to move end effectors to get desired end action

12. Ronin Challenges
Euphoria-controlled bodies soar through DMM materials like ghosts
The Force (driven by Havok) rips Stormtroopers to shreds

13. Ronin
Physics engines interacting

14. Simulating Fire Fire is a tough phenomenon to simulate.
Big trade-off between process time and making it look realistic.
Three Main Methods:
Particle-Based
Fluid-Based
Flame-Based

15. Particle-Based Fire Simulation
Uses particle systems
Move particles upwards from the base of the flame
Uses a user-defined velocity field
Change aspect ratio over time
Change shape over time
Advantages: relatively fast, realistic looking
Disadvantages: need many particles, fuzzy outlines

16. Fluid-Based Fire Simulation
Uses vector/scalar fields described by CFD (Computational Fluid Dynamics)
Velocity Field
Density Field
Temperature Field
Each field is based off of Navier-Stokes equations
The density field is rendered while the temperature field is used to determine color
Advantages: very realistic, shows smoke
Disadvantages: very slow, complex handling

17. Flame-Based Fire Simulation
A single flame is used as fire primitive
Represent fire as a set of flames
Advantages: fast, scalable, somewhat realistic, sharp outlines
Disadvantages: not physically correct, not as realistic as other methods

18. Simulating Explosions
Methods that will be discussed:
Tree-Approach
Fluid-Based

19. Tree-Approach to Explosions
Model the explosion as a tree.
Each node represents an "explosion event"
The parent node represents the larger, initial explosion.
Each child is also an explosion that is usually smaller than the parent node explosion.
The child node events are triggered after some time t after the parent event is triggered.

20. Fluid-Based Explosion Simulation
Very similar to the fluid-based fire simulation.
Makes use of the same three fields: velocity, density, and temperature.
Once again, the density field is rendered and the temperature field determines color.
Difference from fire - parameters
Velocity vectors in all directions
Color schemes

21. Physics in Applications - Review
Covered basics of Unity w/ PhysX
Discussed how rigid body collisions work in Blender
Gave examples of 3rd party engines in XNA *

22. This week - Demos Farseer Physics: 2D collision detection in Unity
Bullet Physics: Keva Planks simulation in Blender *

23. Farseer Physics
2D collision detection built off of Box2D (C++ engine).
Implemented in C# for Unity and XNA
Can be downloaded and imported as package for Unity *

24. Farseer Physics
Primary components involve scripts for FSBodyComponent (collision body properties) and FSShapeComponent (collider shape).
Tutorial by catsinthesky.com *

25. Farseer Physics
More complex colliders possible through concave/convex components.
Uses array of transform points and generated sub-polygons. *

26. Farseer Physics
Distance Joint: simple joint that maintains a constant distance between two points in a body.
Each sphere is a FS body bound to its neighbors.
Can be static to keep a body at a fixed position *

27. Farseer Physics
Revolute joints: Two bodies share common anchor point (hinge).
Single degree of freedom set.
Modifications can be made to motor speed and angle limits. *

28. Blender Simulations based on Bullet Physics.
Developed by physics team Phymec
Python scripts control rigid bodies. *

29. Blender
Keva planks made up of rectangles bound by simple rectangular colliders.
Projectile balls in sphere colliders.
Both act as rigid bodies controlled by gravity vector.
Colliders stacked on each other cause chain reaction. *

30. Physics in Unity Based on Nvidia PhysX Supports: Rigidbodies
Unbreakable, colliders do not change
Softbodies
Interactive modifiable colliders
Joints
Hinges, Ball-sockets, Limbs
Cloths
Interactive Cloths, Skinned Cloths (animations)
Ragdoll Wizard

31. Meshes Geometry representing a 3D object
Can be created from scratch as a set of vertices and faces
Can be imported as .FBX, .dae, .3DS, .dxf, or.obj files
All models will be converted to triangle meshes

32. Colliders Used to detect collisions of game objects
Multiple types of colliders:
Box Collider
Sphere Collider
Capsule Collider
Wheel Collider
Mesh Collider
Does not need to match object renderer

33. Rigidbodies Enables game objects to act under control of physics
Allows forces to be applied to gameobject
Variables for rigidbody properties:
Mass
Drag (Air Resistance and Angular)
Interpolation (smoothes movement)
Kinematic
Collision Detection
Freeze Position, Rotation
Materials (Friction,
Bounce)

34. Colliders Vs. Rigidbodies
Usually use both collider and rigidbody on game object
Useful for playable characters and interactive objects
Collider only is called static collider
Has no physics properties
Useful for objects you want to interact
with but don’t move
Level geometry
Almost never use only rigidbody
Kinematic Rigidbody
Variable on rigidbody that turns off forces and gravity on object
Useful for scripting animations on rigidbodies

35. Physics Manager Gravity Sleep Penetration Solver Iteration Count
Object put to sleep if not moving enough
Penetration
How deep object must be intertwined before collision occurs
Solver Iteration Count
Accuracy or joints and collisions
Layers
Sets which layers of gameobjects interact with each other

36. Forcemode Demo Force Acceleration Impulse VelocityChange
Add a continuous force to the rigidbody, using its mass.
Acceleration
Add a continuous acceleration to the rigidbody, ignoring its mass.
Impulse
Add an instant force impulse to the rigidbody, using its mass.
VelocityChange
Add an instant velocity change to the rigidbody, ignoring its mass.