Particle Systems

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.

• 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.

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.

Enabling this feature makes the following: a random image from the albedo texture is picked up for every particle.

Flipping of random emitted particles horizontally (along the X axis).

Flipping of random emitted particles vertically (along the Y axis).

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.

• 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.

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 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.

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.

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.

Angular velocity of particles, in degrees per second.

• Positive numbers rotate the particles clockwise.
• Negative numbers rotate the particles counterclockwise.

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.

Screen size mode to be used for particles. This mode defines whether the maximum and minimum sizes of emitted particles should be limited relative to screen size or not (e.g., to avoid cases when snowflakes or raindrops obscure the view if they are too close to the camera or when they become invisible as the distance to the camera increases). Three modes are available:

• None - minimum and maximum sizes of particles on the screen are not limited.
• Width - minimum and maximum sizes of particles on the screen are limited relative to screen width.
• Height - minimum and maximum sizes of particles on the screen are limited relative to screen height.

Minimum screen size to be set for particles limiting the minimum fraction of the screen a single particle can occupy:

• 0 (minimum) - the particle has a zero size and therefore is invisible on the screen (occupies no space at all).
• 1 (maximum) - the particle occupies the whole screen.

Maximum screen size to be set for particles limiting the maximum fraction of the screen a single particle can occupy:

• 0 (minimum) - the particle has a zero size and therefore is invisible on the screen (occupies no space at all).
• 1 (maximum) - the particle occupies the whole screen.

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

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

Bit mask for interaction with Particles Field nodes (Deflectors and Spacers). Emitted particles will be affected by a Particles Field only if their masks match (one bit at least).

To participate in the scene dynamics, particles should have a certain mass in kilograms. This value defines the intensity of the impact of the physical node on the particles flow.

• With the mass of 0, the trajectory of particles is not affected by any external physical forces (deflectors work regardless of the mass).
• The more the mass, the heavier the particles are, and the less physical nodes can decline their flow, stretch them, or otherwise affect.

Strength of particles bouncing off an obstacle. This option is very convenient for simulation of some water effects that include splashes. The strength the bouncing effect depends on both the restitution parameter of particles and the value of the restitution surface parameter set for the colliding object (Properties -> Parameters -> Restitution), or the restitution value of a Particles Deflector.

• With the minimum value of 0, the particles does not bounce off.
• With the maximum value of 1, the angle of particles fall equals the angle of their bouncing off.

Roughness of the surface of an obstacle the particle collides with. It determines whether the particles scatter in different directions or react as a uniformly directed flow.

• The minimum value of 0 means the trajectory of all particles after the collision is the same.
• The maximum value of 1 means the particles will scatter in different directions and a bit angularly. This angle arising from particle roughness also affects bouncing behaviour. In contacts of particles with a Particles Deflector its roughness value is also taken into account.

Enables collision detection with the whole shape of a particle.
If particles are big enough, this method is more preferable than Intersection, as it provides a higher degree of visual realism: particles react according to the set parameters, when their edge or vertex comes in contact with an object. Collision calculations are more expensive, so big particles systems should use this option carefully.

Collisions are detected for matching collision bit masks.

Enables detection of physics intersections with particles. Physics intersections can be used, for example, to detect collisions of spawned particles with physical shapes and bodies or static collider surfaces to ensure proper interaction, or as a quick way to detect collisions for raycast-wheels of a simulated ground vehicle, or to check if a destructible object or a player was hit by a projectile.

Physics intersections are detected for matching Physics Intersection bit masks.

Defines positioning mode to be used for child nodes (decal or field) using the procedural texture, to which the particle system is rendered. The following values are available:

• Manual - position of a child decal/field node can be changed manually
• Auto - position of a child decal/field node, which uses the procedural texture, is automatically defined by the position of particle system and cannot be changed manually

Defines relationship between the particle system and a Decal / Field node, that uses the procedural texture into which the particle system is rendered:

• Parent - the decal/field node is a parent of the particle system
• Children - the decal/field node is a child of the particle system

Specifies resolution of the procedural texture into which particles are rendered.

• 128x128
• 256x256
• 512x512
• 1024x1024
• 2048x2048
• 4096x4096
• 8192x8192
• Custom activates additional fields for specifying a custom resolution.