PhysX Switch Operator

Path: Particle View > Add or select PhysX Switch.

Use the PhysX Switch operator to adjust the pure simulation animation by defining events containing this operator as kinematic (particle motion driven by standard Particle Flow actions) as opposed to dynamic (particle motion driven by the PhysX simulation engine). You can also exclude the global gravity forces for the particles in the event, and adjust position/speed/rotation/spin by using standard (non-PhysX) Particle Flow operators. With the Match options you can adjust particle properties in the simulation. The adjustments have some limits because, for example, you cannot match particle position if particles collide with each other (overlapping restrictions).

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

Match Position or Speed group

Use these settings to adjust the simulated positions or speeds of particles. The PhysX engine calculates the simulated motion of the particles in the event, but if Position or Speed is on, then the position or speed particle properties, as defined by regular (non-PhysX) operators, affect the simulation.

Position/Speed - A single PhysX Switch operator can allow non-PhysX actions in the event to affect particle positions or speeds, but not both. Choose one or the other, and then adjust the remaining group controls as necessary. Only one of these can be on; to disable, click the active check box.

• Position - Particle position, as defined by a position-type operator, is used to calculate the necessary force to be applied to a particle in order for the particle to get to the specified position. The force is then applied to a particle in the PhysX engine. This way the desired particle placement is achieved by physics-simulation means.

• Speed - Particle speed, as defined by a speed-type operator, is used to calculate the necessary force to be applied to a particle in order for the particle to achieve the desired velocity. The force is then applied to a particle in the PhysX engine. This way the desired particle speed is achieved by physics-simulation means.

Note: In order for the PhysX Switch position/speed matching to take effect, the PhysX Switch operator should be above the PhysX World operator in the event, and the position- or speed-type operators that define the particle properties to match should also be above the PhysX Switch operator. This way the desirable position/speed is calculated first, then PhysX Switch calculates the necessary forces to be applied to a particle and relays the information to a PhysX World operator.

Also, in general, avoid using a PhysX Force operator in the same event, as it can disturb position/speed matching because both the PhysX Force and PhysX Switch operators use forces applied to particles for motion simulation.

[Duration] - Choose whether the Position/Speed option should be in effect throughout the event, or during a specified frame range, or during explicit intervals. When using In Interval or Animatable, also set the Sync By option to determine how to apply the frame range(s).

• In Interval - The position/speed matching occurs only during the specified frame range.

• Event - The position/speed matching occurs throughout the event containing the PhysX Switch operator.

• Animatable - When you choose this option, the Active button becomes available. You can animate toggling of the Active button by standard keyframe methods to specify multiple frame ranges during which the Position or Speed switch control is active.

Sync By - When using the In Interval or Animatable option, use Sync By to choose the time frame to use: 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 Limit - When using the Position option, specifies the maximum allowed particle speed while PhysX Switch tries to achieve the declared position via simulation.

Match Rotation or Spin group

Use these settings to adjust the simulated rotations or spin rates of particles. The PhysX engine calculates the simulated motion of the particles in the event, but if Rotation or Spin is on, then the operator calculates torque forces to be applied to particles to match the effect of rotation/spin-type operators above the PhysX Switch operator in the event. These controls work the same as those in the Match Position Or Speed group; for details on all except the Spin Limit control, see the preceding section.

Spin Limit - When using the Rotation option, specifies the maximum allowed particle spin in degrees per second while PhysX Switch tries to achieve the declared rotation via simulation.

Apply Anti-Gravity group

If the PhysX World operator has the Apply Gravity option on, you can turn on Apply Anti-Gravity to relieve particles temporarily from the effect of gravity. The timing of "gravity relief" is defined by the time parameters in this group, similar to the timing setup in the Match Position Or Speed group.

Turn Off Simulation group

You can use this option to convert the particle simulation temporarily from dynamic to kinematic. Dynamic particles' animation and movement is defined by the PhysX simulation, while the animation of kinematic particles is driven instead by the standard Particle Flow operators. However, kinematic particles can influence dynamic particles because the shape and motion of kinematic particles is accounted for in the simulation: Kinematic particles can collide with dynamic particles, thus affecting their simulated motion.

The PhysX engine does not control motion of the kinematic particles, so their shapes can overlap. This can create a potential problem if particles are kinematic in one event and dynamic in the next. The shape operator can create a "motion explosion" when the particle move to the next event, because PhysX engine has to resolve the overlapping of collision shapes that occurred while particles were kinematic.

The Turn Off Simulation timing can be controlled by the timing parameters in the group, similar to the timing setup in the Match Position Or Speed group.