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This operator calculates and applies forces necessary to make particles chase a leader.
You can use the second input to specify the leader(s), or use the parameters on the Leader tab to choose a group in the first input as the leader(s).
The Follow POP merges the particle streams from the first and second input.
The Leader parameter on the Leader tab let you choose how the leader works:
The "leader" can be a computed point based on the leader particles (the spatial center of the leader particles, the center of mass, or the center of density).
Each particle in the leader stream can lead individual particles from the follower stream. Houdini can automatically assign followers to leaders, or you can set a
followattribute on particles to determine which leader they will follow. Use the Property POP to set the follow-related attributes on particles.
This force is similar to the Attractor POP. This tool should be used when you want to attract particles to a moving object, whereas the attractor tool should be used when you want to attract particles to a static object.
Turns this node on and off. The node is only active if this value is greater than 0. This is useful to control the effect of this node with an expression.
Note that this is activation of the node as a whole. You can’t use this parameter to deactivate the node for certain particles.
Controls how the node affects the follower particles.
For particles of unit mass, the velocity for the next frame will be towards the specified position with a speed equal to that of the leader.
Applies unit force towards the leader. This will cause the particle speed to continually increase if the leader does not turn.
Stop particles closer than this distance to the leader.
If you enter a value greater than 0, particles further than this distance from the leader will NOT follow.
If the speed of the leader falls below this value, this is used as the target speed instead.
If the distance to the leader is less than this value, the force is repulsive. Otherwise, it is attractive. To make this parameter available, you must set the Behavior to Accelerating Follow.
Particles will try to predict the leader’s direction on the next frame and head it off.
Stop At Leader
Particles come to a complete stop when they reach the leader.
Scaling factor for the force applied to the particles.
Scaling factor for the target speed.
Subset of points from the first input to act as leaders. You can use this parameter instead of connecting the second (Leader) input.
Specifies what the particles follow.
Particle Spatial Center
The center of the box bounding the leader particles.
Particle Center of Mass
The center of mass of the leader particles.
Particle Density Center
The center of mass of the leader particles, with all particles having equal mass.
Each following particle follows a leader particle. If
attributes on the
follower particles, they will use the attribute to
decide which leader to follow (using the Follow
index parameter below). Otherwise, Houdini will
automatically assign followers to leaders.
This parameter is available when Leader is "Individual Particles". It controls how the node interprets the
attribute on particles to assign followers to leaders.
Particles that do not have
follow attributes are assigned
to leaders automatically, using particle order to refer to a
follow attribute on the follower particles refers
to the particle ID of the leader they should follow.
follow attribute on the follower particles refers
to the position of the leader particle in the list of
particles. In a particle system where leader particles
are dying and points are being reused, this could mean
the leaders change as particles die (even if they are
not in the leader stream).
The particles that will be made to follow the leader.
The particles that define the leader(s) to chase. If you do not connect this input, you must set the Leader Group parameter on the Leader tab.
Standard POP local variables
The seconds a particle in the template has been alive.
AX AY AZ
Acceleration of the particle.
BBX BBY BBZ
The point’s relative position in the bounding box.
Point is dead.
Processing iteration number.
A collision for this particle was detected (for example, by the Collision POP) during the processing of this timestep (that is, this iteration of the particle simulation). This variable is cleared at the beginning of each timestep. Note that the collision POP actually detects any collisions which would have occurred the during the previous frame.
Percent of total life used (from 0 to 1).
Expected lifetime of particle.
MAPU MAPV MAPW
Point or vertex texture coordinates.
Total number of points.
Total number of points in source group.
NX NY NZ
The point number of the currently processed point. The
PT is not constant like
ID; it changes based on the number of points.
RESTX RESTY RESTZ
The rest position.
The sliding state of the particle.
Elasticity of a point.
Point is stopped.
1 if particle is stuck to a collision object.
TX TY TZ
Surface UV values.
VX VY VZ
Point spline weight.
Distance from particle to last collision.
HCR HCG HCB
Diffuse color at the collision point on the surface the particle collided with.
ID for last collision. You can control how this attribute is set in the Collision or Limit POP to help distinguish types of collisions.
The time at which the last collision occurred.
The texture map UV coordinates for the surface location where the last collision occurred.
HNX HNY HNZ
The normal at the surface location where the last collision occurred.
HTX HTY HTZ
World space position of the last collision.
The UV coordinates for the surface location where the last collision occurred.
Number of times the particle has collided.
Added by Color POP
Point or vertex alpha value.
CR CG CB
Diffuse point or vertex color.
Added by Property POP
Charge of the particle.
Point is clinging to geometry.
Leader to follow.
SCALEX SCALEY SCALEZ
Added by Proximity POP
Either the point number or id of the particle nearest to this one.
The distance to the nearest particle.
The number of particles within a specified proximity to this particle.
Added by Rotation POP
ROTX ROTY ROTZ
Added by Source POP
ID number, which always remains constant.
Original Source point was birthed from.
Parent’s ID Number.
Added by Speed Limit POP
Added by Sprite POP
Sprite rotation around view axis (in degrees).
Texture coordinate of sprite’s lower-left corner.
Size of sprite in texture space.
Controlled by Suppress Rule POP
Suppress default position rule.
Suppress default velocity rule.
Suppress default up-vector rule.
Suppress default aging rule.
1 if particle is suppressing its default rotation rule.
1 if particle is suppressing its default angular velocity rule.
Added by Up Vector POP
PVX PVY PVZ
UPX UPY UPZ
Absolute speed of particle.