**Description:**

The following example shows the default Final Step Update script with detailed comments.

**Can Be
Used With:**

Used by PF_Source as default Final Step Update script.

**Effect:**

The default script modifies particle speed and direction, causing particles to follow a bulb-shaped path:

*
Example:*

--Get the current particle system executing the script

pf_node_current = particleFlow.scriptRunner()

--In case the current particle system is a valid node...

if (pf_node_current != undefined) then (

--Get the total number of particles

count = pf_node_current.NumParticles()

--Loop from 1 to the number of particles

for i in 1 to count do(

--Set the particle index in the container to the current i value.

--This makes the i-th particle in the container the current one:

pf_node_current.particleIndex = i

--Get the age of the particle, multiply by 5 and use as angle

--to define the particle speed

--Decreasing the constant 5 will slow down the rotation

--Increasing the constant will speed up the rotation

age = 5*pf_node_current.particleAge

--Calculate a factor variable based on the particle age

--This variable will define the radius of the bulb and will vary

--thanks to the sine of the age over time.

--Change the constant 20 to change the radius.

factor = 20*(sin(2*age)+1)

--Finally, calculate and set the particle position

--using the factor as Radius and the particle index as Angle

--in the function of the circle. The position of the node has to be

--added to move the particles to the origin of the Source.

--Info: In general, a circle can be drawn using an Angle

--going from 0 to 2*Pi and the following functions for X and Y:

--X = CenterX+Radius*Cos(Angle)

--Y = CenterY+Radius*Sin(Angle)

--In our case, CenterX and CenterY are 0, Radius is set to factor,

--and Angle is based on the particle index multiplied by 77.

--The Z position is based on the age.

pf_node_current.particlePosition = [factor*cos(77*i), factor*sin(77*i), -age] + pf_node_current.pos

)--end i loop

)--end if

**See
also**