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The main topic here will be the settings in the Extras panel in the Particle sub-context, but we will also speak about using textures, vertex groups or Ipo curves.

  • Particles may interact with other objects (e.g. collide) or be influenced by force fields. You can confine this interaction to a group of objects. Also you can configure the behavior of particles after collisions. Force fields and collision objects have to share a common layer with the particle system.
  • You can use Vertex Groups to control a multitude of particle attributes, especially the density of the particles. Zero density means zero particles.
  • Size and mass of particles govern their physical behavior. E.g. if you have an object attached to the particle you normally don’t want to collide the center of the object, but it’s border.
  • Particle attributes can be animated, especially material animations are important for a good visualization. An animation of 100 frames in the Ipo window is done in the lifetime of each particle. This is the default setting in Blender and is called relative time. You may change this assignment with the Time settings.
Blender3D FreeTip.gif
Time is difficult
You will save yourself a lot of headache if you read the section about time carefully. Many problems with the particle system are related to the difficult time concept.


  • Many of the particle attributes may not only be controlled with a vertex group, but also by a texture, e.g. the emission time, life time or the density.


Time

A particle has a certain lifetime. It is emitted, lives and dies. If you animate certain particle attributes they do not change in the absolute time of your animation, but for each particle individually during it’s lifetime. We have seen examples for this in various tutorials.

Sadly this is not always the case. I will list the cases which are animated that way, and also some of the important cases where absolute time is used.

Relative time is used by:

  • The particle Ipos with the exception of E_Freq.
  • The material attributes of the particle material.
  • Object Ipos (only the object Ipos!) for object visualization of particles. You can use object Ipos for individual animations.

Absolute time is used by:

  • The E_Freq particle Ipo channel.
  • Material Ipos for an object (so you can’t change the color of an object in relative time).
  • Pose Ipos for armatures (this is really a pity).


The Extras Panel

Image 1: The Extras panel in the Particle sub-context.

Effectors

  • GR: Limit effectors (force fields and collision objects) to objects in a group.
  • Size Deflect: Use particle’s size when it deflects from a surface, instead of the center of the particle.
  • Die on hit: Particles die when they hit a surface, i.e. stop their movement and disappear. This holds true also for attached objects. If you want to render a particle (or object) after it’s death, you have to activate the Died button in the Visualisation panel.
  • Sticky: Particles stick to the object they hit, i.e. if the object moves, it carries the sticky particles.


Time

These settings govern the mapping of Ipo curves to particle time. Preset is relative object time, 100 frames of Ipo animation are mapped to the lifetime of the particles. The lifetime of the particles is relative to the object time, which is by default the same as the global time. But you can change the object time, e.g. with a Time Ipo.

  • Global: Particles are calculated in global time, independent from the object time (but still relative to the particle).
  • Absolute: All Ipos that effect particles are calculated in absolute time, and are no longer mapped to the particle time (but may depend from the object time).
  • Loop: Particles are reborn once they die.
  • Tweak: A multiplier to the physics calculation timestep length, with 1.0 one frame corresponds to 1/25 seconds (for a render done at 25 fps), 2.0 doubles the speed, etc.



Other

  • Seed: An offset in the random table that is used for random things in the particles. All random functions in Blender are pseudo random, the randomness is calculated with an unambiguous function. So if you let particles emit with Random, all systems are exactly synchronized and would occupy the same space if their emitter is at same place. With the Seed value you can initialize the random function with different values.
  • Size: The size of the particles. Size may seem a bit strange setting since particles are nearly by definition point-like, but the size may be thought of as the particles’ area of influence (reactor targets etc.) and the size is also used to scale different visualizations like objects, groups and billboards. Size does not affect the Halo rendering of particles.
  • Rand: Gives a random variation to the size.
  • Mass from size: Multiply particle mass with its size, so you can create particles with varying mass.
  • Mass: Mass is used in physical calculations, a resistance against acceleration…

If you use a Hair system, you have two additional settings in the Extras panel. Hair can react directly to force fields, even without using softbodies.

  • Stiff: The stiffness of Hair systems when a force field is applied.
  • Children: Applies force fields to children, and not to the parent particles.


Textures controlling particle attributes

Image 3: Controlling the emission of particles with a texture.

Instead of using vertex groups you can control many of the particles parameters with a texture. The button PAttr (“particle attributes”) only appears in the Map To panel if you’ve created a working particle system.

You may use only Orco or UV in the Map Input panel, if you set other input coordinates then Orco will be used silently instead.

The result of the texture is depending on the value of DVar (“Destination variable”). E.g. for density the default value is 1, if you want to adjust this value with a texture you have to set DVar to zero. The notable exception of that rule is the Time parameter, this is directly set with the value of the texture.

  • Time: The emission time in relation to the Sta/End values. A texture value of 0 means emission at the beginning, a value of 1 emission at the end.
  • Life: Multiplication factor (0 to 1) for the lifetime of the particles. Since 1 is the default value, you can only lower the lifetime with a DVar less than 1.
  • Dens: The density of particles. Since particles have a default density of 1, you can only lower the density with a DVar less than 1.
  • IVel: Multiplication factor for the initial velocity. This doesn’t change the direction, only the value. So if you want to randomize the emission speed but still want the emission in the normal direction, this is what you need.
  • Rough: Factor for the roughness of the children.
  • Size: Factor for the size of the particles.
  • Kink: Factor for the kink frequency of children.
  • Length: Factor for the length of the children.
  • Clump: Factor for clumping of the children.


Ipo channels

The Ipo type Particles does only appear if the active object carries a particle system.

All Ipo channels with “E_…” are working for the emission, the others are working during the lifetime of the particles.

  • E_Freq: Emission frequency, the number of particles per frame. The total amount of particles is still set with the parameter Amount, also the Start and End frame is not changed by that. This is the only channel that is independent from the life time of the particles, it is evaluated in absolute time. All other channels are (by default) evaluated in relative time.
  • E_Live: Factor for the lifetime of the particles.
  • E_Speed: Factor for the emission speed of the particles.
  • E_Angular: Factor for the emission rotation of the particles, it needs also Dynamic to be set.
  • E_Size: Factor for the emission size.

The following channels change the behavior of the particles during their lifetime.

  • Angular: Rotation speed.
  • Size: Size.
  • Drag/Brown/Damp: According to the parameters in the Physics panel.
  • Length: Only for Path visualization (Hair systems or Keyed particles): length of the hair.
  • Clump: Only for Path visualization with Children: parameter Clump for the Children.
  • GravX/GravY/GravZ: Parameter AccX/AccY/AccZ in the Physics panel.
  • KinkAmp/KinkFreq/KinkShape: Only for Path visualization with Children.
  • BBTilt: Only for Billboard visualization: tilt of the billboard.
  • F-parameters: Regarding forcefields which are produced by particles. The same as for objects.
  • f2-parameters: Since particles can produce two force fields, the settings for the second force field.


Controlling particle parameters

An overview about the possibilities to set particle parameters is given in the following table. Setting parameters with a texture means PAttr on in the Map To panel, else the name of the Ipo channel or the Vertex group attribute is stated. A blank field means that you can’t influence the parameter by that method.

What can effect what
Emit Ipo Particle Ipo Texture Vertex group
Emission time E_Freq Time
Emission location Dens Density
Lifetime E_Life Life
Starting speed E_Speed IVel Velocity
Angular velocity E_Angular Angular TanVel/TanRot
Size E_Size Size Size Size
Length Length Length Length
Gravity (Acc…) GravX/Y/Z
Brownian force Brown
Damping Damp
Drag Drag
Clump Clump Clump Clump
Kink amplitude KinkAmp
Kink frequency KinkFreq Kink Kink
Kink shape KinkShape
Rough Rough Rough
Billboard tilt BBTilt