Lecture 9 (Particle Systems)

Question 1

What is the primary use of the geometry shader (introduced in DirectX10)?

Answer 1

To create new primitives from existing ones

Question 2

What is the geometry shader most powerful in?

Answer 2

Creating particle systems

Question 3

What is a Particle System?

Answer 3

A collection of many small particles that together represent a fuzzy object

Question 4

Over a period of time, what happens to particles?

Answer 4

Particles are generated into a system, move and change from within the system, and die from the system

Question 5

Give examples of where particle systems have been used.

Answer 5

Computer graphics in cinema, animations, digital art and video games

Question 6

What are particle systems used to model?

Answer 6

Various irregular types of natural phenomena;

• Fire
• Smoke
• Waterfalls
• Fog
• Bubbles
• Explosions

Question 7

What are the two main criteria that particle systems follow?

Answer 7

• Collection of particles

- Stochastically defined attributes

Question 8

What is the Collection of particles criteria?

Answer 8

• A particle system is composed of one or more individual particles
• Each of these particles has attributes that directly or indirectly affect the behaviour of the particle or ultimately how and where the particle is rendered

Question 9

What are the Stochastically defined attributes criteria?

Answer 9

• The introduction of some type of random element via stochastic limits (bounds, variance, distribution)
• This random element can be used to control the particle attributes

Question 10

What are the Particle Attributes?

Answer 10

• Emission (speed, spread, rate)
• Lifespan (infinite, constant, variable)
• Opacity (static, dynamic)
• Colour (static, dynamic)
• Size
• Shape

Question 11

What are the stages of the Particle Life Cycle?

Answer 11

• Generation
• Dynamics
• Extinction

Question 12

What is Generation in the Particle life cycle?

Answer 12

• Particles in the system are generated randomly within a predetermined location of the fuzzy object
• This space is termed the generation shape of the fuzzy object, and this generation shape may change over time
  
  • Particles can originate from different points in the frame within the fuzzy object
• Each of the above-mentioned attributes is given an initial value
  
  • These initial values may be fixed or may be determined by a stochastic process

Question 13

What is Dynamics in the Particle life cycle?

Answer 13

• The attribute of each of the particles may vary over time
• In general, each of the particle attributes can be specified by an equation with time as the parameter (time and attributes make particles dynamic instead of static)
• Particle attributes can be functions of both time and other particle attributes

Question 14

What makes particles dynamic and not static?

Answer 14

Time and attributes

Question 15

What is Extinction in the Particle life cycle?

Answer 15

• When the particle age matches its lifetime it is destroyed

Question 16

What are the criterias for terminating a particle prematurely?

Answer 16

• Running out of bounds
  
  • If a particle moves out of the viewing area and will not re-enter it, then there is no reason to keep the particle active
• Hitting the ground
  
  • It may be assumed that particles that run into the ground burn out and can no longer be seen
• Reaching a threshold
  
  • e.g. if the particular colour is so close to black that it will not contribute any colour to the final image, then it can safely be destroyed

Question 17

What will happen if you render the entire life cycle of each particle simultaneously?

Answer 17

This will result in static (instead of animated) particles, useful to simulate certain materials, such as hair, fur or grass

Question 18

How to achieve particle simulations?

Answer 18

Sprite (2D) particle systems

Voxel (3D) particle systems

Question 19

What are Sprites?

Answer 19

A textured quad

Question 20

How to control Sprite’s dimensions and position?

Answer 20

• Sprite dimensions
  
  • Width and height of sprite
• Anchor point position
  
  • Used to position the sprite (anchor point is usually top left)

Question 21

What are Voxels?

Answer 21

Essentially 3D pixels

- More complex than sprites

Question 22

Where are voxels widely used?

Answer 22

In cinema

Question 23

What is the downside of voxels?

Answer 23

Computationally challenging