Doc:2.4/Manual/Physics/Particles/Types

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Emitter

The Emitter system works just like its name says: it emits/produces particles for a certain amount of time. In such a system, particles are emitted from the selected object from the Start frame to the End frame and have a certain lifespan. These particles are rendered default as Halos, but you may also render these kind of particles as objects or strands (depending on the particle’s physics, see Visualization).

Options

Basic

• The two buttons next to the field type activate rendering resp. show the particles in the 3D window.
• Amount: The maximum amount of parent particles used in the simulation.
• Sta: The start frame of particle emission. You may set negative values from version 2.48 on. This enables you to start the simulation before the actual rendering.
• End: The end frame of particle emission. Remember that you have to set the Bake values also if you need the simulation in other frames than 1 to 250.
• Life: The lifetime (in frames) of the particles.
• Rand: A random variation of the lifetime of a given particle. The shortest possible lifetime is Life×(1-Rand). Values above 1.0 are not allowed. For example with the default Life value of 50 a Rand setting of 0.5 will give you particles with lives ranging from 50 frames to 50×(1.0-0.5)=25 frames, and with a Rand setting of 0.75 you’ll get particles with lives ranging from 50 frames to 50×(1.0-0.75)=12.5 frames.

If you want to control the emission over time, you can use an Ipo Curve (see Controlling Emission, Interaction and Time).

Emit From

These parameters define how the particles are emitted, giving precise control over their distribution. You may use vertex groups to confine the emission, that is done in the Extras panel. You may also control the particle emission with an (animated) texture.

• Emitter element: Verts/Faces/Volume: States that particles are emitted respectively by vertices, faces, or the enclosed volume of the mesh emitter.
• Random: The emitter element indices are gone through in a random order instead of linearly (one after the other).
• Even: Particle distribution is made even based on surface area of the elements, i.e. small elements emit less particles than large elements, so that the particle density is even.
• Distribution:
  • Jittered: Particles are placed at jittered intervals on the emitter elements.
    • Amount: Amount of jitter applied to the sampling.
    • P/F: Number of emissions per face (0 = automatic).
  • Random: Particles are placed randomly in the emitter’s elements.
  • Grid: Particles are set in a 3d grid and particles near/in the elements are kept.
    • Resol: Resolution of the grid.
    • Invert: Toggles what is considered to be the emitter.

Usage

You use an emitter system when you need a lot of identical moving elements, for example: a particle fire (Tutorial) where you use the particles to create flames and sparks. Some other applications where you would use an emitter are: smoke rising from a fire or cigarette, ants issuing from an anthill, bats flying out of a cave, etc.

Reactor

Using a Reactor implies you are using at least two particle systems, because reactor particles are born, or created, as a result of the actions of another particle system. The other particles may have come from another particle system on this object, or a particle system on a separate object.

The system that reacts is called the “Target”.

You should use a Reactor particle system in the places where you used children with the older implementation of particle physics.

By having the reactor produce particles upon the death of particles in the other system, you can create particle cascades.

Usually (not with emit from particles), the target particle’s size determines it’s area of influence (Size button in the Extras panel).

You should set up the particle systems starting with the last one in a chain, so if you have a cube with pSysOriginator that targets a sphere with pSysTarget, you should be sure to set up pSysTarget before you set up pSysOriginator. Systems that create a loop, for instance pSysOriginator → pSysTarget → pSysOriginator, will probably cause problems, since one target system won’t be updated before the system that targets it is.

Options

Basic

• Sta/End: Particles are only emitted when the chosen event happens (see React on, below). But with this option, you can force all remaining particles to be emitted within the Sta through End frames (the proper settings are displayed when this option is active).
• React on: Which event of the target particles triggers emission: Death (target particle dies), Collision (target particle collides), or Near (target particle in the vicinity of the Reactor).
• Multi React: Allows reacting multiple times (alive particles react too and not just unborn particles).
• Shape: How reaction strength varies with distance from target particle. The closest, the strongest the reaction.

Emit From

These parameters are mostly the same as the Emitter particle system type, to one exception:

• Emitter element: Particle is another possible option for Reactor particle systems, meaning that particles are emitted by other particles, when reacted on.

Target

These parameters are only useful for Reactor systems, and are meant to define the particle system to which the Reactor system should react.

• OB: Defines the object that has the target particle system, whose particles are evaluated in search for events to react to. If the field is blank, the current object is used.
• Psys: Selects which particle system is the target. Should appear red when no valid target is specified. This is always the case when the current particle system is the first particle system of the current object (OB: field empty).

Usage

Interesting examples of reactions:

• React on - Death: Particles are emitted when the target particles die. Two example usages:
  • Fireworks: Target particles are emitted upwards with normal gravity. Reactor particles are set to emit from particles with random initial velocity and similar gravity.
  • Minefield: Reactor particles emitted from a large volume with reactor initial velocity. Target particles that die inside the volume cause “explosions” when they die.
• React on - Collision: Particles are emitted when target particles collide with something. Example usage:
  • Raindrops: Reactor particles are on the ground plane with normal and reactor velocity. Target particles fall from above and collide with the ground plane.
• React on - Near: Particles are emitted when target particles are near them. Example usages:
  • Trails: Reactor particles set to emit from particles with random initial velocity. Now the reactor particles are always “near” the target particles so they emit constantly leaving a trail for the target particles (Image 3b).
  • Sand dunes: Reactor particles are emitted from the ground mesh with negative reactor velocity. When target particles fly over the ground they make reactor particles rise from the ground.

• Tutorial no. 1: Fireworks
• Tutorial no. 2: Fireworks.

Hair

This particle system creates only static particles, which may be used for hair, fur, grass and the like. Only this system may be edited interactively in the 3D window (in Particle Mode), only this system may be animated as softbody.

The complete path of the particles is calculated in advance. So everything a particle does a hair may do also. A hair is as long as the particle path would be for a particle with a lifetime of 100 frames. Instead of rendering every frame of the particle animation point by point there are calculated control points with an interpolation, the segments.

Options

• Set Editable: The system will become editable in Particle Mode. You can’t change the number of particles or the particle physics if you have set the hair editable. If you need to change these things later all changes in Particle Mode will be lost.
• Amount: Use as little particles as possible, especially if you plan to use softbody animation later. But you need enough particles to have good control. For a “normal” haircut I found some thousand (very roughly 2000) particles to give enough control. You may need a lot more particles if you plan to cover a body with fur. Volume will be produced later with Children.
• Segments: The number of segments (control points minus 1) of the hair strand. In between the control points the segments are interpolated. The number of control points is important:
  1. for the softobdy animation, because the control points are animated like vertices, so more control points mean longer calculation times.
  2. for the interactive editing, because you can only move the control points (but you may recalculate the number of control points in Particle Mode).

10 Segments should be sufficient even for very long hair, 5 Segments are enough for shorter hair, and 2 or 3 segments should be enough for short fur.

Usage

• We deal with the production of longer hair on the page Hair.
• Fur Tutorial, which produced (Image 4b). It deals especially with short hair.