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Fields > Drag |
This creates a Drag field.
Fields > Drag > 
This sets the options when you create a Drag field.
Magnitude
Sets the strength of the drag field. The greater the magnitude, the greater the braking force on the moving object.
Attenuation
Sets how much the strength of the field diminishes as distance to the affected object increases. The rate of change is exponential with distance; the Attenuation is the exponent. If you set Attenuation to 0, the force remains constant over distance. Available in Attribute Editor only.
Speed Attenuation
Weakens the amount of drag when the speed of the particle is less than the Speed Attenuation value. This allows slow moving particles to not be affected much by the drag, while heavily damping still occurs with fast moving ones.
Use Direction
Specifies that the braking force is exerted only against the object’s velocity that lies along Direction X, Y, Z. Available in Attribute Editor only.
For example, if you turn on Use Direction and your object is moving in the same direction as the drag force, the full braking force of the drag field is applied to it. If the object is moving perpendicular to the drag force, no braking force is applied. If the object is moving in the opposite direction, it speeds up.
Direction X, Y, Z
Sets the direction of the drag force’s influence along the X, Y, and Z axes. You must turn on Use Direction for Direction X, Y, and Z to take effect.
Inherit Velocity
The amount that drag is relative to the movement of the drag field. The drag field is like a block of air, water or mud, depending on the magnitude. The Inherit Velocity attribute allows this block to move when the field is transformed.
If Inherit Velocity is set to 1.0 then it moves exactly with the field. If the magnitude is high, then any objects in the range of the field are pulled with it, like pebbles stuck in mud. It works similarly to Inherit Velocity on the Air field, only it more accurately tracks the entire transformation and includes scaling and shearing of the transform. It also does not require that you have a secondary wind velocity the way the Air field does.
Inherit Velocity on the Drag field is useful for a variety of effects:
- You could parent the field to a moving object. As the object moves, the field will create a wake for the object, dragging nearby particles or fluid with the object motion. This can help stabilize hair on a head, for example. To some degree it fakes hair-to-hair collision behavior next to the head.
- You could drag cloth in motion next to an object. You could create a drag field parented to each joint in a skeleton, where each field is volume-bounded and scaled to overlap the cloth. This would allow you to damp cloth relative to the large-scale motion of a character.
- The Inherit Velocity attribute on the Drag field can be animated to keyframe particle motions in a manner that still lets the particles behave in a dynamic fashion. It can act like a hand that grabs particles, pushes or twists them and then releases them. An explosion could be created by animating the field's scale. Similarly, it could be used as a type of dynamic constraint; for example, tugging on bits of cloth then releasing.
Motion Attenuation
Reduces the effect of drag when the field is moving slowly. When motion attenuation is greater than zero there is no drag when the field is stationary. When the speed of the field is equal to or greater than the Motion Attenuation value then the full magnitude setting of the drag is applied. This only has an effect when Inherit Velocity is not zero.
Distance
Use Max Distance
If you turn on Use Max Distance, connected objects within the area defined by the Max Distance setting are affected by the drag field. Any connected objects outside the Max Distance are not affected by the drag field. Available in Attribute Editor only.
If you turn off Use Max Distance, all connected objects are affected by the drag field, no matter how far away they are from the drag field.
Max Distance
Sets the maximum distance from the drag field at which the field is exerted. You must also turn on Use Max Distance for Max Distance to take effect. Available in Attribute Editor only.
Falloff Curve
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See Falloff Curve.
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Volume shape
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See Volume shape.
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Special Effects
Available in the Attribute Editor for object fields only.
Apply Per Vertex
Sets where the field emanates from the object. If you turn on Apply Per Vertex, each individual point (CV, particle, vertex) of the chosen object exerts the field equally at full strength. If you turn off Apply Per Vertex, the field is exerted only from the average position of the specified points.
If you are using the Attribute Editor, open the Special Effects section to display the Apply Per Vertex attribute. Available in the Attribute Editor for object fields only.