Follow Spline

Target Spline

Here you link to a spline to which the particles should react. The assignment can be made via drag & drop from the Object Manager or you can first click on the pipette symbol on the right-hand edge of the linking field and then on the spline object in the Object Manager.

Invert Spline Direction

Some modes of this modifier allow the particles not only to be attracted by the assigned Target Spline, but also to follow its course. The point sequence on the spline is taken into account and the particles follow the direction of the spline by default. Activating this option reverses this effect and causes the particles to fly in the opposite direction to the spline.

Mode

Force: An attractive force acts between the particles and the spline curve, deflecting the particles in their trajectory and accelerating them towards the spline. Parameters such as the Effect Radius can be used to restrict the area in which this attractive force acts in the area of the spline.

Here, a Force acts between the particles and the Blume spline, which permanently pulls the particles in the direction of the spline, but does not move the particles tangentially to the spline.

Guide: The spline attracts the particles and binds them to its shape. The particles follow the course of the spline exactly. This makes it possible to precisely pre-draw the desired particle flight with a spline. Since the particles fly exactly along the spline, an additional Swarm Modifier can be used after the Spline Modifier, for example, to force the particles to maintain a distance from each other. This allows a certain volume to be maintained within the particle flow and therefore also around the spline. Otherwise, the third mode, Rail, also offers a special behavior exactly for this purpose.

The Guide mode pulls the particles in the direction of the spline and then guides the particles exactly along the spline curve. In this example, a Swarm Modifier was also used to give the particle flow a volume along the Flower spline.

Rail: Basically, this mode works in the same way as Guide. The particles are also attracted to the spline here and then follow its course. However, the original distances between particles and spline are retained in this mode. This therefore also allows a wide stream of particles to fly along the curve, as shown in the following video. This mode also offers an additional Rail link, which can also be used to control the alignment of the particles. This effect can be seen in the second video.

In Rail mode, the distance determined when the particles enter the spline's area of influence is retained. In this way, wide particle streams can also be moved along a spline.

In Rail mode, a Rail spline can also be used - shown here in light blue - which can also be used to control the rotation of the particle flow along the Target Spline.

Mix[0..100%]

In the Guide and Rail modes, this can be used to set the influence on the original particle flight direction. With large Mix values, the change in the direction of flight takes place more quickly and the particles follow the splines even more precisely. At a Mix value of 0%, the particles are no longer affected.

Rail

This field is only available in Rail mode and enables the linking of a second spline, which should have a distance to the Target pline. The imaginary area between the two splines is then used for the alignment of the particle flow and thus enables, for example, a twisting of the particle flight around the Target pline. The video above gives an example. The volume of the particle flow or the orientation of the individual particles is not affected by the Rail spline. How Rail is to be evaluated for calculating the alignment is controlled by the following two options.

Invert Rail Direction

This means that the Rail is evaluated against its natural direction of travel, i.e., against the order of its points.

Use Closest Point on Rail

Normally, the Target Spline and Rail spline are evaluated identically for the particle flow. The alignment of the particles located in the center of the Target Spline is then also carried out with respect to the center of the Rail spline, for example. This standard behavior is always suitable when using Rail Mode, for example, if the Rail spline was created from a copy of the Target Spline or was drawn along the Target Spline. Alternatively, by activating this option, the section of the Rail spline closest to the particles can be used for alignment.

Rail Effect Radius Multiplier[0..+∞%]

This setting is only available in Rail Mode if Source Closest Point is used. This percentage value refers to the Effect Radius and is used as a multiplier for this. As values above 100% are generally used here, the Rail Effect Radius Multiplier is used to define a safety distance to the Rail from which the particles cannot escape.
With an Effect Radius of 200 cm in combination with a Rail Effect Radius Multiplier of 150%, this means that a safety radius of 300 cm is created around the Rail spline in which forces are exerted on the particles.
Despite the relatively small Effect Radius, particles further out can still be reliably captured.

The following video shows the same particle simulation on the left and right. On the left a Rail Effect Radius Multiplier of 200% was used, on the right only 100% was used. On the right, this means that some particles can detach from the spline that lie outside the Effect Radius.

Effect Radius[0..+∞m]

Particles must move within this distance of the Target Spline to be captured by the modifier. The behavior of particles that leave this area of influence can be defined via the Exit Behaviour setting.
If you use a Rail to control the particle trajectories, an additional Rail Effect Radius Multiplier can be configured for this, which also binds particles that are further away to the rail.

Source

Here you select the mechanics with which the velocities and flight directions of the particles are to be calculated:

Closest Point: Starting from the particle, the closest point along the Target Spline is determined. In Force Mode, the particle is then accelerated in the direction of this spline position. This speed is added to the existing speed of the particle. The final velocity of the particles is therefore not limited. If, on the other hand, the Guide or Rail modes are used, the tangents of the Target Spline at the closest spline position play a role. Their direction is multiplied by the Follow Strength value to calculate the new flight direction and speed of the particles. The old flight speed of the particles is replaced. This means that there can be no uncontrollable acceleration of the particles due to the summation of the original and new velocities.

Closest Point is used here in combination with Rail. The particles are emitted at high speed at the left edge of the screen and are then slowed down according to the Follow Strength as you follow the spline.

Age: This mode is only available in Guide and Rail modes. The Age of the particles is read out and - after it has been multiplied by the Source Scale - transferred to the Target Spline. This creates a target position on the spline for each particle age. The start of the spline corresponds to the value 0 and the end to the value 1. As the Age is measured in seconds, the particles with a Source Scale of 1 would completely fly off the entire spline after just one second. Therefore, in most cases, a much lower Source Scaling should make sense.

Here, Age is used in combination with Rail. The blue ball symbolizes a target position along the spline, which moves across the spline every second(Source Scale = 1). With the reversing Exit Behavior, the particles that reach the end of the Target Spline are sent in the opposite direction along the spline back towards the start of the spline. The sequence is repeated.

Age Percentage: This mode is only available in the Guide and Rail modes and works in a similar way to Age. Here, however, the Age Percentage of the particles is equated with a target position along the spline. This means that the particles always reach the end of the spline exactly at the end of their lifetime if Source Scaling 1 is used. Particles with a 20% expired lifetime are therefore attracted from the position that is 20% of the spline length away from the starting point of the spline. This makes it possible, for example, to animate fast and slow particles along the Target Spline by varying the Lifetime within a particle stream, as in the following video.

Here, particles were colored according to their Lifetime assigned at the emitter. Short-lived particles appear reddish, long-lived particles bluish. By evaluating the Age Percentage, the short-lived red particles must fly down the spline faster than the long-lived blue particles so that each particle reaches the end of the spline exactly at the end of its life (with a Source Scale of 1).

Source Scale[0.00..+∞]

This setting is available for the Source modes Age and Age Percentage as a multiplier. In the Age Percentage mode demonstrated in the video above, a Source Scale of 0.5 would mean that the particles only fly half of the spline at the end of their life and therefore only reach the center of the Target Spline at the end of their life. With a Source Scale of 1, on the other hand, all particles reach exactly the last point on the Target pline at the end of their life.

Segment

This setting defines how Target or Rail splines that have several segments are evaluated. This setting is therefore irrelevant for splines that only consist of one segment:

Closest: The segment closest to the particles is always used automatically. This review takes place continuously and screen by screen.
Specific: The segment to be used for the calculation can be selected via the Segment Index input. The first segment of a spline always has the index 0.
Random: A randomly selected segment on the target or Rail spline is evaluated for each particle. This random selection is determined once when a particle enters the area of influence of the Target Spline. The following video shows an example of this.

Random or Next: This mode is a mixture of the Random and Next functions. The segment closest to the particles is always preferred. If the distances between a particle and the segments are similar, a random decision is made as to which spline segment should act on the particle. This decision between a random and a close segment selection is smoothed. There are therefore no jumps in the influence on the particles if, for example, a spline with several segments moves within a particle stream.

Here, two splines bent in opposite directions were combined into one and used as the Target Spline. By using the random Segment mode, the particles are distributed randomly over the two segments, which results in an even distribution of the particle flow.

Segment Index[0..2147483647]

If you have selected Segment Specific, you can enter the index number of the desired segment here. The counting method starts with 0 for the first segment of the spline.

Attract Strength[-∞..+∞]

This controls the general strength with which the particles are drawn along the spline in the direction of the calculated target position. In Force and Guide modes, the particles are pulled directly in the direction of the spline according to this strength. In Rail mode, the Attract Strength controls the force of attraction to the calculated position in the vicinity of the spline, depending on the position of the particle at the time it entered the spline's area of influence. The strength can also be varied via the Attract Falloff or an individual Attract Map.
The following video shows the effect of different Attract Strength settings in Force mode.

Here, particles are sent through a circular spline, which exerts a force on the particles. On the left, a medium Attract Strength was selected, on the right a large one. The greater the Attract Strength, the faster the particles reach their targets and the lower the chance that they can escape from the spline's area of attraction.

Attract Falloff[0..100%]

This allows the force of attraction to be varied depending on the distance of each particle from the target point. The percentage value refers to the Effect Radius of the modifier. The higher the percentage value selected, the greater the reduction in the Attract Strength for particles in the vicinity of the spline. For this reason, the default value of 0% is selected here so that all particles within the Effect Radius are influenced to the same extent. However, increasing the value can also be used to separate particles, as in the following video. Once again, particles are attracted by a Circle spline. Due to a 20% Attract Falloff, however, only the particles in the vicinity of the spline are attracted with full strength. More distant particles therefore have a better chance of escaping the force of attraction.

Here, particles are sent through a circular spline, which exerts a force on the particles. An increased value for Attract Falloff reduces the attraction force depending on the distance of the particles to the spline. This increases the chance that particles can escape the attractive force of the spline.

Attract Map

This allows the Attract Strength along the spline to be varied individually. To do this, create a Vertex Map for the Target Spline. Their values are multiplied by the Attract Strength.

Here, particles are attracted by a rectangular spline where only two of the corner points have a 100% vertex map weighting. The remaining two cornerstones have a weighting of 0%. The forces of attraction vary accordingly along the spline.

Follow Strength[-∞..+∞]

This is the strength with which the particles are moved along the Target Spline in the Guide and Rail modes. This intensity can still be varied automatically via the Follow Falloff or via an individual Follow Map.

Follow Falloff[0..100%]

This allows the Follow Strength to be varied depending on the distance between the particles and the spline. The percentage value refers to the Effect Radius of the modifier. A comparable effect also exists for the Attract Strength.

Follow Map

A Vertex Map of the Target Spline can be assigned here, the weighting values of which are multiplied by the Follow Strength. In this way, the Follow Strength can also be varied individually along the spline.

Here, particles are attracted by a rectangular spline on which only two of the corner points alternately have a 100% vertex map weighting. The remaining two cornerstones have a weighting of 0%. The sequence strengths vary accordingly along the spline.

Variance Strength[0..100%]

Variance Frequency[0..+∞%]

These settings can be used to randomly vary the influence of the particles. The frequency controls the frequency with which the intensity of the particle influence is varied and the strength regulates the intensity of the variation.
A higher frequency means that the intensity of the influence on the particles changes more quickly.

Align Mix[0..100%]

When moving along the Target Spline, the particle axis systems can also be aligned tangentially to it. To do this, increase this percentage value. At 0% there is no alignment of the particle systems at all and at 100% the Z-axes of the particles are aligned perfectly parallel to the respective spline section. The following video demonstrates this effect. The first half of the simulation uses a mix value of 0%, which is then increased to 100% in the second half of the video. Accordingly, the particles covered with pyramids are oriented to the curve.

Here the particles follow a spline. In the first half of the video, the particles remain in their original orientation. By increasing Align Mix to 100%, the particles in the second half of the video will then align themselves with the course of the spline.

Exit Behaviour

This menu defines what should happen after the particles reach the end of the spline curve when following it:

Continue: The particles retain their last flight direction and flight speed that they had at the end of the spline or spline segment. With closed Target splines, this can also be used, for example, to send the particles flying along the spline again.
Turn Around: This mode is only available with Source Age or Age Percentage and causes the particles to fly a small curve when reaching one of the spline ends and then fly along the spline again in the opposite direction.
Go to Start: This mode is only available with Source Age or Age Percentage and causes the particles to return directly to the start of the spline when they reach the end of the spline and then follow the spline again.
Kill: The particles are automatically deleted when leaving the spline or segment.
Switch Group: You can define a different particle group for the Target Group to which these particles should be moved when leaving the spline or segment.

Here the particles each follow a circular arc. From left to right, the modes Continue, Kill and Switch Group were selected for the Exit Behavior, which changes the behavior of the particles at the end of the arcs.

Target Group

When selecting Switch Group for Exit Behavior, a particle group can be assigned here to which the particles should then automatically switch when they reach the end of the Target Spline. If you want the particles to automatically switch to a new particle group, you can also use the Create Group button, which you can find below.

Create Group

Use this button to create a new particle group, which is then automatically assigned as the Target Group.