POP Lookat dynamics node

A POP node makes a particle look at a point.

On this page	Parameters Target Bindings Inputs Outputs Locals Examples
Since	13.0

The POP Lookat node reorients a particle to look at a given point or direction.

This operator modifies the orient, torque, targetw, and spinresist attributes.

Parameters ¶

Activation

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

This is activation of the node as a whole. You can’t use this parameter to deactivate the node for certain particles.

Group

Only affect a group of points (created with, for example, a Group POP or Collision Detection POP) out of all the points in the current stream.

Target ¶

Mode

The target can be either specified as a position in space to look at or a direction to look in. In both cases, the z-axis of the particle will be reoriented to face that point or direction.

Target

The goal for the particle to look in.

Reference Direction

The particle axis which will be aligned to the look at direction. For example, setting this to 1,0,0 will align the particle’s X-axis to the look at target.

Reference Object

The object that determines the space of the target position. If your target position is 0,0,0, the particle will look at the center of this object.

Use Up Vector

Allows you to disable use of the up vector. This allows the particle to rotate in a shorter direction to the target facing, but it might not maintain the same sense of up.

The up vector with which the particle should align. Will be overridden by an up attribute.

Reference Up

The original up vector of the particle. This parameter can be used with Reference Direction to set an alternate reference frame for the particle before it is aligned to the look at target.

Method

How to re-orient:

Immediate

Instantaneously face the desired orientation. Useful for initializing orientations, but jerky if applied in animation.

Turn

Re-orient the particle but cap the total it can spin to a maximum number of degrees per second. Useful for spinning a particle to an orientation precisely without worrying about overshoot.

Spin

Applies a torque on the particle for it to spin into the desired direction. You will likely want to add a Spin Drag POP to compensate.

Degrees per Second

How fast, in degrees per second, that the particle should reorient.

Note

There is no physics in this reorientation, so there is no overshoot or acceleration.

Torque Scale

A scalar for how quickly to accelerate when spinning into the desired orientation. This will use physics, so will overshoot. You will want to add a Spin Drag POP to avoid oscillating forever if Treat as Wind is disabled.

Treat as Wind

Rather than treating the computed torque as an amount of torque to add to the particle’s angular velocity, treat it as a wind speed to be matched by the particle. This causes the particle to spin up to the goal speed, avoiding overshoot.

Spin Resistance

How strong of an influence to have on the spin of the particle. Higher values will cause it to match the goal angular velocity faster. This is also used to do a weighted average when competing winds are applied to the same particle.

Bindings ¶

Geometry

The name of the simulation data to apply the POP node to. This commonly is Geometry, but POP Networks can be designed to apply to different geometry if desired.

Evaluation Node Path

For nodes with local expressions, this controls where ch() style expressions in VEX are evaluated with respect to. By making this ., you can ensure relative references work. It is important to promote this if you are embedding a node inside an HDA if you are also exporting the local expressions.

Inputs ¶

First Input

This optional input has two purposes.

First, if it is wired to other POP nodes, they will be executed prior to this node executing. The chain of nodes will be processed in a top-down manner.

Second, if the input chain has a stream generator (such as POP Location, POP Source, or POP Stream), this node will only operate on the particles in that stream.

Outputs ¶

First Output

The output of this node should be wired into a solver chain.

Merge nodes can be used to combine multiple solver chains.

The final wiring should go into one of the purple inputs of a full-solver, such as POP Solver or FLIP Solver.

Locals ¶

channelname

This DOP node defines a local variable for each channel and parameter on the Data Options page, with the same name as the channel. So for example, the node may have channels for Position (positionx, positiony, positionz) and a parameter for an object name (objectname).

Then there will also be local variables with the names positionx, positiony, positionz, and objectname. These variables will evaluate to the previous value for that parameter.

This previous value is always stored as part of the data attached to the object being processed. This is essentially a shortcut for a dopfield expression like:

dopfield($DOPNET, $OBJID, dataName, "Options", 0, channelname)

If the data does not already exist, then a value of zero or an empty string will be returned.

DATACT

This value is the simulation time (see variable ST) at which the current data was created. This value may not be the same as the current simulation time if this node is modifying existing data, rather than creating new data.

DATACF

This value is the simulation frame (see variable SF) at which the current data was created. This value may not be the same as the current simulation frame if this node is modifying existing data, rather than creating new data.

RELNAME