Lecture 9 (Particle Systems) Flashcards
What is the primary use of the geometry shader (introduced in DirectX10)?
To create new primitives from existing ones
What is the geometry shader most powerful in?
Creating particle systems
What is a Particle System?
A collection of many small particles that together represent a fuzzy object
Over a period of time, what happens to particles?
Particles are generated into a system, move and change from within the system, and die from the system
Give examples of where particle systems have been used.
Computer graphics in cinema, animations, digital art and video games
What are particle systems used to model?
Various irregular types of natural phenomena;
- Fire
- Smoke
- Waterfalls
- Fog
- Bubbles
- Explosions
What are the two main criteria that particle systems follow?
- Collection of particles
- Stochastically defined attributes
What is the Collection of particles criteria?
- 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
What are the Stochastically defined attributes criteria?
- 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
What are the Particle Attributes?
- Emission (speed, spread, rate)
- Lifespan (infinite, constant, variable)
- Opacity (static, dynamic)
- Colour (static, dynamic)
- Size
- Shape
What are the stages of the Particle Life Cycle?
- Generation
- Dynamics
- Extinction
What is Generation in the Particle life cycle?
- 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
What is Dynamics in the Particle life cycle?
- 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
What makes particles dynamic and not static?
Time and attributes
What is Extinction in the Particle life cycle?
- When the particle age matches its lifetime it is destroyed
What are the criterias for terminating a particle prematurely?
- 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
What will happen if you render the entire life cycle of each particle simultaneously?
This will result in static (instead of animated) particles, useful to simulate certain materials, such as hair, fur or grass
How to achieve particle simulations?
Sprite (2D) particle systems
Voxel (3D) particle systems
What are Sprites?
A textured quad
How to control Sprite’s dimensions and position?
- Sprite dimensions
- Width and height of sprite
- Anchor point position
- Used to position the sprite (anchor point is usually top left)
What are Voxels?
Essentially 3D pixels
- More complex than sprites
Where are voxels widely used?
In cinema
What is the downside of voxels?
Computationally challenging
