The Ultimate Houdini node reference
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The Pop Attract node will attract particles to positions and geometry.
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The Pop Attract is great for getting particles to follow something. The key to using this node is understanding the various attraction types along with the difference between force methods.
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-- This acts like an on/off switch.
- Allows you to isolate the pop attract force based on groups. For more information about groups, check out the Group Node Bible Entry.
-- Position = Particles will be attracted to a specific position in x,y,z. The "Goal" is the x,y,z coordinates. The "Goal Velocity" is not mentioned in the user documentation, and its use is unclear. It appears correlate with "ambient speed" parameter when the force method is set to "follow," but it will not indicate directionality. Avoiding the "Goal Velocity" parameter would be generally advised.
-- Particles = The particles are told to follow a collection of other particles within the DOP network. You can specify which particles to follow by using groups or streams. Goal and goal velocity are present when this is selected - HOWEVER - they will not do anything unless you change the attraction type back to Position.
** Match Method = When the match method is set to "Average Position," then it will average the positions of all particles. If you turn the clumps above 1, then it will make clusters with averaged positions, and the particles follow the closest position. Point per-particle uses a different method which directly links particles based on an attribute value. In other words, the attributes need to match up in order for the particles to follow them.
-- Points = Points will use sop geometry as an attractor for the particles. Select the geo source that you'd like to use along with the point group field to isolate which points you want the particles to move towards. See above in the "Match Method" section for what that does. Goal and goal velocity are present when this is selected - HOWEVER - they will not do anything unless you change the attraction type back to Position.
-- Surface Points = This does the same exact thing as "Points" except that it allows you to switch which primitive it should follow. In practice, this is useful for when you want it to switch over to a new primitive to follow mid-simulation. The UVW is confusing, and does not refer to "UV" space. Instead it is referring to parametric space, and unless you're a mathematician, then it's best to leave this alone and assume that it's following the center of the target primitive.
-- Accelerate = The point's velocity is changed gradually over time by a force. This is not the same as having a target velocity because the particles will go faster and faster towards the target over time. The Force Scale will turn up the amount of force being applied to the particles at each step.
** The Reversal Distance allows you to apply a force in the opposite direction of the target once the particles are ______ meters away.
** In order to understand the "Peak Force Distance," first understand that as particles get close to the target, their force is reduced gradually. The Peak Force Distance is asking you how far away a particle needs to be before the force starts reducing.
** The maximum distance is how far away the target is allowed to influence the particles. If a particle is outside the target distance, then it will not be attracted to the target.
-- Follow = The Follow force method features confusing language in the user documentation, so keep in mind that it may be more difficult to understand this section than the accelerate method. In practice, the "Follow" force is better for situations where you don't want the particles to overshoot the target. Overshooting the target is a problem when using the "Accelerate" method, so that's why the "Follow" method was created.
** The Force Scale is a scale on the forces applied to the particles. The higher you turn this up, the more force will be pushed onto the particles towards the goal
** Minimum Distance = Once a particle is ___ away from the target, the pop attract will try to slow that particle down to 0. This is the primary setting which will help you prevent particles from over-shooting a target.
** Maximum Distance = If particles find themselves outside the maximum distance, then they will not be affected by the pop attract.
** Ambient Speed = Use this parameter as a speed limit to your particles. Particles will try to follow this speed as they follow the target.
** Speed Scale = Applies a multiplier to the ambient speed. This may be a useful parameter to adjust when using vexpressions.
-- If this is checked on, all particles are treated equally. If this is off, then particles with a greater @mass value will be affected less than particles with a lower @mass value.
-- Allows you to use vex when altering the values within the force tab.
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Bindings can be used to tell which nodes are allowed to work with each other. Nodes which belong to the same geometry name are allowed to work with each other.
As an example, if you set the binding on a pop source to "goobie" and leave everything else at its defaults, no other node in your dop network will want to work with the popsource because they have a different binding name. If, however, you go to your solver and change its binding to "goobie" as well - now the pop solver will work with the pop source node. Lastly, if you set a pop force's binding to "goobie", that will now allow the pop force to interact with the pop source node. NOTE: Global forces (ex: the Gravity DOP) do not feature any bindings and will work on all data within the dop network.