Lesson 10 – Particle systems
PV227 – GPU Rendering
Jiˇrí Chmelík, Jan ˇCejka
Fakulta informatiky Masarykovy univerzity
08. 12. 2015
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Particle System
general name of a large number of techniques that simulate
natural phenomena such as smoke, dust, fireworks, rain, etc.
composed of a large amount of small particles that move together
in a way which is characteristic of each type of phenomenon
we usually maintain the position as well as other attributes for
each particle (velocity, color, etc) and perform the following steps
once per frame:
1 update the attributes of each particle – involves math calculations
(ranging from very simple to very complex (depending on the
complexity of the phenomenon))
2 render the particles (as simple colored points or full blown texture
mapped billboard quads).
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Particle System . . .
Old way:
Update of particles on CPU, rendering on GPU.
pro – we can calculate whatever behaviour of particles we want
con – we need transfer data from CPU to GPU each frame →
performance hit
side-step way:
everything is solved on GPU
necessary data are stored in texture
pro – no need to transfer data
con – bulky solution, we are limited in what we can store in texture
New way:
everything is solved on GPU
necessary data are stored in Transform Feedback Buffer
pro – more elegant solution
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Transform Feedback Buffer
special type of buffer where we can send transformed primitives
from geometry shader (or vertex shader if there is no GS)
plus – we can decide whether the primitives will also continue on
their regular route to the rasterizer.
The same buffer can be connected as a vertex buffer in the next
draw and provide the vertices that were output in the previous
draw as input into the next draw.
We don’t know number of primitives in buffer
we don’t care...
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Transform Feedback Buffer scheme
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Fixed Particles
render the particle as a point,
update their position based on time,
optionally texture the point.
Figure: Particles representing stars in t = 0.
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Iterative Particles
render particles as points,
update their position based on previous position.
Figure: Emanating 64 × 64 particles in t = 1.f
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Particles via Transform Feedback Buffer
Firework with three types of particles
updating position, velocity, TTL of particles
Figure: Shells and secondary shells (no visual distinction)
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