Lecture "Game Physics" in Game Design and Development course at University of Management and Technology Lahore by Hafiz Ammar Siddiqui

1. Game Physics
Game Design and Development
By Hafiz Ammar Siddiqui
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2. Game Physics
• Game physics adds laws of physics into a game
• Close approximation of real physics which is implemented with discrete values
• Use of numerical methods using actual physics equations to get the results close to physics
we observe in real life
• Update the state of objects based on physical calculations
• Compute forces and motion of objects in a scene
• Compute mechanical interactions between objects in a scene
• Physics inside a game is usually handled by a physics engine

3. Basic Physics Terms
• Speed: Rate of change of position with time (scalar)
• Velocity: Rate of change of position with time (vector)
• Acceleration: Rate of change of velocity with time (vector)
• Mass: Amount of matter contained in a body (scalar)
• Force: That changes or tends to change the state of rest or motion of a body (vector)
• Torque: Force that causes rotation of an body around its axis (vector)
• Momentum: Quantity of motion in a moving body or mass in motion (vector)

4. Mechanics
Statics
Kinematics
Kinetics

5. Mechanics (Classical Mechanics)
• Branch of physics that is concerned with the motion of bodies, its causes and its effects
• Discipline of physics that quantifies motion, and explain it in terms of forces, energies
and momentums
• Study of motion of bodies when subjected to forces or displacements, and their
subsequent effects on environment
• Mechanics is classified into three main types
• Statics
• Kinematics
• Kinetics

6. • Study of a body in the state of motion
(without considering the forces causing
the motion)
• There is acceleration in kinematics
• Does not consider mass, force and torque
• Deals with basic geometry of motion
Kinematics
Mechanics
• Study of a body in the state of motion
(considering the forces causing motion)
• There is acceleration in kinetics
• Considers mass, force and torque
• Deals with cause of motion
• Often referred as dynamics
Kinetics
Mechanics
• Study of a body in the state of static equilibrium (rest or in uniform motion)
• There is no acceleration in statics
Statics
Mechanics

7. Collision Collision Detection
Collision Response

8. Collision
• A process in which two or more bodies intersect (overlap) with each other or are about
to intersect (overlap) with each other
• Occurs when distance between two or more bodies falls below a threshold value
• In games, bounding volumes (colliders) are used to define the shape of a body for
collision based calculations. A body can have multiple bounding volumes in union.
Box bounding volume Polygon bounding volume Multiple box bounding volumes in union

9. • Process of determining whether two or more bodies have run into each other or not
• Detects the intersection of two or more bodies or their bounding volumes
• Finds out if two or more bodies or their respective bounding volumes are overlapping
with each other or not
• Computational geometry problem involving the calculation of whether and where two or
more bodies have collided or they are about to collide
• In games, its divided into two basic types
• Discrete Collision: Determine whether bodies are colliding at current time or not
• Continuous Collision: Predict the exact point and time of collision between bodies
Collision Detection
Collision

10. Collision Detection
Collision
No collision at current time No collision at current time
but upcoming collision in future
Collision at current time Collision at current time
Before
After
Continuous CollisionDiscrete Collision

11. • How bodies will react to collision
• Simulate what happens when a collision is detected between bodies
• Estimate using laws of physics that what will happen after a collision
• Determines if position, rotation or shape of collided bodies will change or not depending
on the collision
• How motion and shape of bodies will change after they have collided with each other
with respect to their properties
• Process of calculating the resultant forces and accelerations of each body with respect to
its mass after collision
Collision Response
Collision

12. Object Physics Rigid Body
Soft Body

13. • A body whose points remain at fixed distances from one another
• It is a dimension based non-deformable body
• Distance between any two points of a rigid body remains constant in time regardless of
external forces exerted on it
• Rigid body translates or rotates as a whole, and there is no relative translation or rotation
among the particles of a rigid body
• It does not change its shape during its motion or when it encounters any collision
• Movement is composed of Linear Trajectory Translation and Relative Rotation
• Examples of rigid body could be a solid brick, stone or rock if we ignore any type of
destruction of respective body
Rigid Body
Object Physics

14. Rigid Body
Object Physics
Rigid body linear trajectory translation (origin movement) and relative rotation (orientation rotation)

15. • A body whose points can change their distances from one another
• It is a dimension based deformable body
• Distance between any two points of a soft body changes with respect to the external
forces exerted on it
• Soft body can stretch or compress in any direction, and there is relative translation or
rotation among the particles of a soft body
• It can change its shape during its motion or when it encounters any collision
• Examples of soft body could be a rubber, fabric or jelly if we ignore any type of cutting of
the respective body
Soft Body
Object Physics

16. Soft Body
Object Physics
Soft body deformation by force

17. References
• Physics for Game Developers - David M Bourg, Bryan Bywalec
• Game Physics Engine Development - Ian Millington