Particle Systems

A particle system is a really versatile technique that allows creating complex moving structures that produce dynamic and "fuzzy" effects. These structures are used for simulation of abstract effects of fire, smoke, explosions, electricity, fountains, rocket trails, flocking, magic, and many many more. All these effects are hard to reproduce using traditional rigid objects: particles are represented not by a set of primitive surface elements, but by point masses forming the volume of particle primitives. Another distinctive feature is that particles are not static — they may change not only their position, but also the form with the time.

A particle system consists of three main entities:

• Emitter — the source that emits particles according to the values set in the Emitter parameters.
• Particles themselves, which are emitted according to the predefined behavior after emission.
• Additional physical effects applied to the particles that affect their behavior.

See also#

To create particles, perform the following steps:

1. On the Menu bar, click Create -> Particle System -> Particles.

   

2. Place the Particles object somewhere in the world.
3. Specify the particles parameters.

The particles emitter's behaviour is set via the Emitter parameters.

Clear On Enable	Enables re-initialization of the particle system each time it is enabled. When this option is disabled, turning on the particle system restores the state it had before it was turned off.
Emitter Enabled	Enables the emitter.
Emitter Sync	Enables synchronization of the child particle system with the parent one, even if the child particle system has the Emitter Enabled option disabled.
Emitter Shape	The shape of the volume within which the particles are generated: Point — particles are emitted from a single point. Sphere — particles are generated at random positions within a sphere that has a specified radius. Cylinder — particles are generated at random positions within a cylinder that has a specified radius and height. Box — particles are generated at random positions within a cube that has a specified width (X axis), height (Y axis), and depth (Z axis). Spark — this emitter generates particles in the points of collision of the parent particles. The spark particle system should be made a child node of a particle system that generates initial particles. Spark emitter can be used to simulate cascades of particles. Random — particles are generated on the surface of an arbitrary parent mesh. The particle system should be made a child node of a mesh. At rendering time, random vertices of the mesh are chosen to generate particles.
Emitter Size	The size of the particles source. The number of fields (whether it is radius or boundary dimensions) depend on the chosen shape.
Particles Type	Billboard represent rotating square planes that are camera-oriented. For example, billboard particles can be used to create smoke. Flat particles are perpendicular to the Z axis of their particle system. They are good for simulating some effects on plane surfaces such as water. Point particles are similar to the billboard type. They also always face the camera, but have the fixed screen-aligned orientation. Length particles are billboard particles that can be stretched along the direction of their movement. Stretching is an adjustable factor. Sparks and splashes can be effectively simulated using this type of particles. Random particles are square particles randomly oriented in the space. Leaf-fall can be successfully imitated with this type of particles. Route particles can be used to create tracks from moving objects (for example, trail following a ship). They are similar to the previous implementation of flat particles. Chain particles are billboard particles that form a continuous, visually uninterrupted flow. Their length directly depends on the spawn rate of the emitter. This type of particles is intended to be used with Emitter Shift creating a chain-like trail after it.
Sequence Order	The order of rendering for particle systems, especially when creating a complex effects like shots (with muzzle flash, smoke and the shot itself, each rendered with different particle systems). This parameter is very much the same as Rendering Order option in the Materials Settings. But it allows setting a rendering sequence inside of the particle system hierarchy, to avoid such situations when the smoke from a distant shot is rendered atop of the fire of the foreground shot. 0 means a default sorting according to bounding boxes of particle systems. Particles with the lowest Sequence number are rendered first and are covered by the particles with the highest Sequence number, which are rendered last and above others.
Emitter Shift	Enabling this checkbox makes the emitter generate particles only when the Particle System is moving.
Emitter Continuous	Enables continuous particles that follow the shift of the emitter.
Texture Atlas	Enabling this feature makes the following: a random image from the albedo texture is picked up for every particle. Notice For using this option, Animation of the texture should be disabled.
Texture Atlas Size	The size of the texture atlas.
Random Flip X	Flipping of random emitted particles horizontally (along the X axis).
Random Flip Y	Flipping of random emitted particles vertically (along the Y axis).
Warming On Start	Toggles on and off the particle system initialization with the illusion of prior activity. The particle system evolves with time, so after encountering it in the virtual world, the system only starts to be generated, particle by particle, until the whole system gains the intended look. When the character comes out on a glade, we will see a fire gradually burn up. Warm start for the particles enables rendering the full-grown particle system straight away. The technical implementation of warm start is the following: when the particle system is initialized on the encounter, its life is computed starting from the generation of the first particle to its disappearance. After that, the particle system is considered evolved and is rendered in this state. The calculations are taken at a fixed frame rate of 25 fps, which is the minimum required for the correct simulation of particle systems (see also information about correlation between framerates). Warm start can be enabled without any detrimental effect for any particles systems, except for huge ones.
Max Warming Time (Sec)	Maximum time of the particle system warmup.
Spawn Rate	Number of spawn actions per second. The value defines how many times a certain number of particles will be spawned in one second. For example, the value set to 5 equals to 5 spawn actions per second. 0 results in no particles at all.
Number Per Spawn	Number of particles to be spawned simultaneously each time according to the Spawn Rate.
Spawn Threshold	Threshold of the number of particles depending on the velocity of the parent particles. This parameter is used to additionally synchronize the number of particles spawned by spark and random emitters with the parent particle system. Notice Threshold for random emitter functions only with a particle system as a parent node. By the value of 0, the spawn rate of the spark emitter is independent of the parent particle system. The higher the threshold value, the higher must be velocity of the parent particles for the sparks to be generated. If it is not high enough, there will be only few particles, if any.
Limit Per Spawn	The total maximum number of particles emitted per spawn. This parameter specifies the number of particles that can simultaneously exist in the world. In other words, the number of particles existing in the world cannot exceed the limit value. For example, if the Number per Spawn value is 10, and the Limit Per Spawn value is 5, 5 particles will be emitted. And no particles will be spawned until the previous ones exist.
Life Time (Sec)	Duration of the particles existence after emission in seconds. This parameter also has the Spread value that creates the variety of the Life Time value, in seconds.
Delay	This option defines the time to pass between the parent system initialization and initialization of the child node. If any delay is set, the parent system starts emitting particles, and after the delay, the generation of child particles is activated. If a particle system doesn't have children, the delay defines the time after which the particles are emitted. This parameter also has the Spread value that creates the variety of delay of particle initialization, in seconds.
Period	Duration of a pause between generation cycles, in seconds. If the value is set to 0, the particles are spawned constantly, without any pauses. If infinity (inf) is specified, the particles emitter becomes inactive after one generation cycle. This parameter also has the Spread value that creates the variety of the Period value, in seconds.
Duration	Duration of generation cycle, within which emission occurs, in seconds. The higher the value, the longer are the periods when particles are generated. Setting the value to 0 means that particles are simultaneously spawned over an infinitely small time interval (i.e. during one frame). This value can be used when you need to simulate a one-particle gun shot, for example. This parameter also has the Spread value that creates the variety of the Duration value, in seconds.
Spread (+/-)	Spread option introduces additional modulation of the corresponding parameter. It represents the range of values that can be randomly added to or subtracted from the specified parameter value.

This set of parameters defines how the particles behave after they are emitted:

Value Setting Options#

Depth Sort	Depth sorting is required, if particles use alpha blending (except for the additive one). If not enabled, then based on the depth buffer data, opaque objects positioned farther can be wrongly rendered in front of transparent particles. With depth sorting, geometry is rendered in the order from back to front, which rules out visual artifacts.
Emitter Based	Enabling this option makes particles move along with the emitter.
Position	Particle position coordinates relative to the emitter along X, Y and Z axes.
Gravity	Gravity force affecting particles along the X, Y and Z axes. Positive values equal gravity vector directed upwards. Negative values equal gravity vector directed downwards. The rotation of particle system node does not affect the gravity vector.
Direction	Direction in which all emitted particles move forming a flow, specified along the X, Y and Z axes.
Velocity	The speed of particles movement in the set direction, in units per second. To grant the natural-looking flow, the final velocity of each separate particle can differ, if the range of values is set.
Linear Damping	The decrease in particles linear velocity over time. This parameter is used to simulate effect of friction of the medium for particles.
Angle	Angle of particles orientation in space, in degrees. If the angle value is set to 180 degrees, the particles will be randomly oriented in all directions. Notice This option is not available for particles of point and length types.
Rotation Speed	Angular velocity of particles, in degrees per second. Positive numbers rotate the particles clockwise. Negative numbers rotate the particles counterclockwise.
Radius	Radius (half-size) of the particle.
Increase In Radius	Increment of the size of a particle, in units per second. Positive numbers result in particles increasingly growing after they are spawned. For example, fireworks grow and blossom in the sky. Negative number define the particles gradually lessening. For example, to imitate the smoke dissipating in air.
Length Stretch	Stretching of a particle billboard, available for the Length Particles. With the value of 0, the length particle is simply a square billboard. Increasing the value stretches particles in the direction of their movement. The result is calculated by multiplying the stretch value by the particle velocity value. So, the higher the velocity is, the more stretched the particles are in the direction of their movement, while the other side remains of the same width. Sparks Length Stretch = 0 Sparks Length Stretch = 0.3
Length Flattening	Makes the Length Particles not camera-oriented as usual billboard particles, but more perpendicular to the Z axis. With the value of 0, the particles are not flattened. With the maximum value of 1, the particles will be flat (perpendicular to the Z axis) when they are emitted. Length Flattening = 0 Length Flattening = 1

Interaction of the particles is limited to the application of forces and collisions with external objects. There are two methods to detect the collision with external objects: by using the Physics Intersection parameter or the Collision parameter.

Particles can be rendered into a procedural texture to be used by an Orthographic Decal or a Field Height. This feature can be used, for example, to create ship wake effects or oil splashes.

The following settings are available:

More intricate changes in further movement of the particles may be performed by applying the additional physical effects. They have influence on the particles flow in the desired direction or on the contrary deflect it. The effects can be of three general types:

• Forces
• Noises
• Deflectors

There is no limitation to the number of additional physical effects applied to one particle system and they can freely overlap, enabling to constitute complex trajectories easily and fast.

Forces#

Noises#

Deflectors#

To create complex effects, it is necessary that all particles systems are synchronized in time. Setting a particle system as a parent node results in the following:

• All particles systems that are child nodes are synchronized relative to their parent particle systems. If the children have children of their own, they still are synchronized with the main parent system, which is the highest in the hierarchy.
• When creating a new child particle system, it should be synchronized with the parent one by disabling and again enabling the parent emitter (Node tab -> Enabled box). At this moment, each of the child systems is initialized with its Emitter parameters (such as generation duration, period of generation pause, and delay of initialization).
• Disabling or enabling the parent emitter (Node tab -> Enabled box) affects all child particle systems: they synchronously stop or start emitting particles (emitted particles still live out their time).
• Disabling or enabling the parent node (Node tab -> Enabled box) also affects all children: all particle systems in the hierarchy are turned off and on — and preserve the same state as was at the moment of their disabling.

Synchronizing Several Particle Systems#

Updating each frame a huge number of objects located far away from the camera that are hardly distinguishable or observed as a mass is a waste of resources.

To improve performance and avoid the excessive load, particle systems simulation can be updated with a reduced framerate. When a particle system is out of the area specified by the Update Distance Limit, particles stop to be updated and freeze statically.

The set of frame rates given below enables you to specify how often the particles simulation should be updated when the particle system is visible, when only its shadow is visible, or when it is not visible at all.

This feature is enabled with default settings ensuring optimum performance and can be adjusted per-object in the UnigineEditor or via API at run time.

If your project, for example, contains an invisible particle system (e.g., using the Viewport mask) and some logic attached to its update (e.g. spawning some visible particles on collision with objects) this logic won't work, as the particle system might be updated with a reduced rate or might not be updated at all. To enable updating such objects regardless of their visibility you can set the Update Distance Limit and corresponding update rate values for it to infinity.

It is possible to create mesh-based particle systems. For that, Mesh Cluster should be added as a child node of the particle system (ObjectParticles). After that, meshes are automatically spawned by the emitter.