PhysX Drag Operator

Path: Particle View > Add or select PhysX Drag.

PhysX Drag is a fast alternative to the PhysX Force operator for adding a slow-down factor to a simulation. With the PhysX Drag operator, you don't need to first create a Drag space warp and then designate it in the PhysX Force operator. Also, PhysX Drag uses native PhysX properties to simulate a friction factor. Last, with a slow-down factor from PhysX Drag operator you can stabilize the simulation (reduce jitter) and make it appear more natural, since it lets you introduce energy dissipation due to friction.

Angular and Linear damping factors specified in PhysX Drag are persistent particle properties — once the operator defines them, they are "attached" to the particles, and stay with them even as they move from event to event. Thus, to define a constant damping factor throughout the simulation, you need only a single PhysX Drag operator, set in the first event with the particles.

Note: In general, place all PhysX operators above a PhysX World operator in an event, so the PhysX properties defined by the operators are known to the simulation engine before the simulation cycle starts.

Interface

Adjust - Sets the PhysX Drag mode. This option is based on the fact that you can animate the Linear and Angular Damping factors, so it's possible for them to change while particles are in the event.

Continuous - Adjusts the damping factors the entire time that particles are present in the event with the PhysX Drag operator. When a particle leaves the event, it retains the last damping factors that were set while it was there.
On Event Entry - Sets the damping factors once per particle, at the moment the particle enters the event, based on the current values.

Damping Factor - Toggle linear and/or angular damping, and set a separate damping value for each.

Linear - Defines the slowdown factor for linear particle movement, affecting particle speed.
Angular - Defines the slowdown factor for angular particle movement, affecting particle spin.

Sync By - When using the Continuous option, use Sync By to choose the time frame in which to apply animation of the damping factors: Absolute Time, Event Duration, or Particle Age. For details, see the main 3ds Max help (for instance, the Scale Operator topic > Animation Offset Keying group section).

Speed Factor Multiplier - Allows an additional damping-factor adjustment, in relation to particle speed. This is useful when particles travel through a medium whose slowdown factor is proportional to the particle speed: the higher the speed, the greater the slowdown factor.

When Speed Factor Multiplier is on, the Speed Unit and Spin Unit parameters become available.

Speed Unit - The speed value in linear units per second at which Linear Damping is applied at the specified value (see Damping Factor, preceding). If the actual speed of a particle is twice the Speed Unit value, then the Linear Damping Factor applied is twice the specified value; it's a direct proportion. The same applies to slow particles: If a particle's actual speed is half the Speed Unit value, then the damping factor applied is half that of the specified value.
Spin Unit - Works the same as Speed Unit but with respect to particle spin rate and the Angular Damping Factor setting. Spin Unit is measured in degrees of rotation per second.

Wiring From Data Channels rollout

To access this rollout, highlight the PhysX Drag operator in the event, then right-click it and choose Use Script Wiring from the menu. This lets you define the Linear and Angular Damping Factor values per particle with a Data operator (from Particle Flow Tools Box#3). The wiring defines damping factor values only; when Speed Factor Multiplier is on, the effect of the multiplier factor is applied on top of that.

Linear/Angular Damping Factor - To define either damping factor with a Data operator, turn it on, click the button and choose an Output New sub-operator that uses the Real type. The sub-operator defines linear or angular damping factor values on per-particle basis.