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Note: This is an archived version of the Blender Developer Wiki. The current and active wiki is available on wiki.blender.org.

Particle System vs. Settings

Particle System is a feature of objects (each object can have multiple particle systems). It provides the context, i.e. the concrete space in which the particles exist. This includes

Memory buffers and caches
Data Links
Overall coordinate system

Particle Settings define the behaviour of the particle systems using them. They define components and properties of

Simulation
Rendering
Realtime Display

Settings are stored in their own library data block and dynamically linked by a particle system. This means that several particle systems can use the same type of particle effect.

Image 1: The main data components of particle systems in a UML-style diagram

Modules

The novel feature introduced here is the Particle Module, which describes a distinct part of particle functionality. They can be combined flexibly by the artist to create the desired effect. Each of the particle settings' tasks has it's own set of modules to choose from.

Focus on simulation

The majority of modules will be defined for the simulation task. Rendering and drawing will usually not require as much customization, but in some cases it can be beneficial.

Simulation

These modules perform a modification of particle data based on a given time-step.

Module interface:

typedef struct ParticleSimulationModule {
    void (*execute)(                   /* Execution function */
      ParticleSimulationData *sim,     /* Common context (psys, parent object, etc.) */
      float curtime,                   /* Current simulation time */
      float timestep                   /* Time step interval */
    );
} ParticleSimulationModule;

Examples
Mesh Emitter	Creates new particles randomly over time and places them on a mesh surface or volume.
Integrator	Takes forces/acceleration and transforms them to velocity/position change. Several different types possible: Euler, RK4, Verlet, ...
Gravity	Simple gravity force.
Effector	Applies force fields from external objects/object groups.
Collision	Does collision test against external objects/object groups and calculates dynamic response (bouncing, friction, etc.). Advanced node modules could separate collision checks from dynamic reactions!
Boids	Applies boid behaviour
Hair	Adds a hair strand to each particle and special simulation of the strand. Like collision, this is quite complex feature and may be split into several components
SPH Fluids	Simulates fluids with the SPH method.

Rendering

Examples
Halo	Simple circular halos.
Billboard	One quad per particle with UV coordinates and normals for advanced shading.
Strands	Used for rendering hair and grass simulated by the hair simulation module.
Surface	Create a rigid mesh surface from particle locations (useful for fluid simulations).
Object	Uses instances of an external object.

Drawing

These modules generate simple OpenGL geometry primitives for display in the 3D window.

Examples
Point	Point display.
Cross	Cross display.
Circle	Visualizes the particle size by the circle radius.
Strands	Shows strands by drawing lines.
Object	Uses instances of an external object.

User:Phonybone/Archive/Modular particle system/System vs Settings