NiPSysGravityModifier

NiPSysGravityModifier is a modifier for particle systems that applies a gravity-like effect on particles in the system. It does so by dragging particles towards a NiNode in the NIF. It is commonly used to mimic the effects of the wind, but can be used to actually pull particles down if the strength is set high enough.

A typical example of a NiPSysGravityModifier.

Its fields are:

• Name: The name of the modifier. Typically used by other modifiers to target each other.
• Order: 4000 seems to be the only one used, it instructs the particle system to update forces from this modifier.
• Target: The particle system you wish to affect.
• Active: If the modifier is enabled. You can animate this value by specifying the name of the modifier as the Controller ID in a NiControllerSequence and using a NiPSysModifierActiveCtlr as a controller with a NiBoolTimelineInterpolator as the interpolator.
• Gravity Object: A NiNode to center the gravity effect on.
• Gravity Axis: Specifies the local axis of the gravity force on the Gravity Object. Seems to be limited to one axis per modifier, works on a float between 0 and 1.
• Decay: How much the effect of gravity wears off over distance away from the Gravity Object. If set to zero, the strength of gravity is fixed regardless of distance.
• Strength: The strength of gravity. The value is units/second².
• Force Type: Either Planar or Spherical, or Unknown. Planar operates parallel to the Gravity Axis and Gravity Object, Spherical implements a spherical field around the Gravity Object.
• Turbulence: Adds a level of randomness to the effects of gravity.
• Turbulence Scale: Multiplies the effects of Turbulence.
• World Aligned: Uses the rotation of the Gravity Object and multiplies it with the value of the Gravity Axis. Seems to be exclusive to Bethesda titles.

NiPSysGravityModifier is typically what is used to give the appearance of particles being pushed by the wind. While BSWindModifier exists and does accelerate particles in the direction of the wind by the wind speed of the weather, the wind direction is only set once in a northwestern direction, making it unideal for prop effects.