1. Introduction to Game Physics1

2. Game Physics Not trying to build a perfect physical model
Most things can be approximated assuming Newtonian physics and rigid bodies
Use discrete simulation (constant step) techniques

3. Why Physics The Human Experience
Real-world motions are physically-based
Physics can make simulated game worlds appear more natural
Makes sense to strive for physically-realistic motion for some types of games
Emergent Behavior
Physics simulation can enable a richer gaming experience

4. Physics of Motion Terms
Position
The vector indicating the location of a point relative to the coordinate system’s origin
Velocity
The rate of change of the position of an object
Acceleration
The rate at which the velocity of an object changes with time

5. Position and Velocity Where is the object at time t (using pixels)?
Computation
position(t) += velocity * dt
Where dt is the amount of time passed since the last Update (either calculated programmatically or via GameTime)

6. Acceleration Where is the objects rate of change (using pixels)?
Computation
velocity += acceleration * dt
Where dt is the amount of time passed since the last Update (either calculated programmatically or via GameTime)

7. Friction and Damping
With no acceleration, velocity will only change based upon user input
To slow objects down without acceleration
* after updating position
Computation
velocity *= rateOfDecay
Where 0.0 < rateOfDecay < 1.0

8. Clamping Keeping a value within a specified range Computation
Prevent the object(s) from traveling off-screen
Prevent the object(s) from moving too fast
Computation
float value = MathHelper.Clamp (
valueToClamp,
minimumValue,
maximumValue);

9. Other Physics Issues User control for jumping height
Input tracking
Sequence on keys/buttons\controller’s currentState and previousState
State driven
JumpingState (velocity can continue to decrease)
FallingState (velocity can only decrease)
Stuck on ground plane
Ground Plane (y > upperLimit could trigger player Death)
Grounded state doesn’t apply gravity but can transition to falling/jumping

10. Simple 2D Physics By Example
Demonstration

11. ?

12. References
Maxim, Bruce R. Computer Game Physics