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OpenTS Manual

VelocityPerturbationCoefficient

How much a railgun trace randomly varies its particles' speed.

Specification
Applies to
ParticleSystemType
File
rules.ini
Section
[<ObjectType ID>]
Value
floating point
When omitted
0.0

A railgun trace adds a random speed offset to each particle’s Velocity as it lays the particle. The offset changes only how fast a Railgun particle travels; its direction is set separately, as MovementPerturbationCoefficient describes. The offset is a fixed amount of speed, not a share of Velocity, so the same setting varies a slow particle proportionally more than a fast one. A Spark particle ignores its speed, and particles of other behaviors do not move in a railgun trace, as The turn describes. Only the Railgun behavior reads this key.

rules.ini
[MyRailgunSys] ; a ParticleSystemType registered in [ParticleSystems]
BehavesLike=Railgun
HoldsWhat=MyRailgunPart ; a ParticleType registered in [Particles]
MovementPerturbationCoefficient=.3
VelocityPerturbationCoefficient=.6 ; speeds vary by at most about .21 either way

The trace lays its particles from the muzzle outward, and each offset builds on the one before:

  1. Start from the previous particle’s offset, or from zero for the first particle.
  2. Add a random amount between -0.5 and 0.5.
  3. Multiply the sum by half this value.
  4. Cap the result at this value, and hold it at or above MovementPerturbationCoefficient negated.

From 0 up to 2, step 3 shrinks the carried offset, so it stays within plus or minus this value divided by (4 minus twice this value). At the stock .6 that bound is about .21, against the stock railgun particles’ Velocity of .4 and .3. The cap in step 4 is higher than that bound for any positive value below 1.5, so it only takes effect from 1.5 up. From 2 up, the carried offset no longer shrinks and drifts out to the cap or the floor.

Below 0, the cap in step 4 is negative. Every particle then starts slower than its Velocity, unless MovementPerturbationCoefficient is 0 or less and the floor in step 4 lifts the offset back up.

Step 3 also sets how closely neighboring particles match. Each particle carries over a fraction of the previous particle’s offset equal to half this value: three tenths at .6. At stock settings each speed is therefore mostly a fresh draw.

The floor in step 4 comes from MovementPerturbationCoefficient, not from this key, so the two limits differ unless the keys are equal. At stock settings the floor never takes effect, because the stock MovementPerturbationCoefficient values of .3 and .4 both lie beyond the .21 bound. Setting MovementPerturbationCoefficient below the bound cuts off the slow side of the range, and at 0 no particle starts slower than its Velocity.

At zero, every particle starts at exactly its Velocity, unless MovementPerturbationCoefficient is negative.

A negative MovementPerturbationCoefficient raises the floor in step 4 above zero, so every particle starts faster than its Velocity by at least the floor: at -.1, at least .1 faster. Where the floor is at or above this value, as it always is when this value is 0, every particle starts exactly the floor faster.

See also — BehavesLike, MovementPerturbationCoefficient, PositionPerturbationCoefficient, Velocity