about the event script in Pt grad dust example

[suntemple]

Just purchased the volume shaders and I can say with much glee that they make particles in XSI 200% more fun and flexible! Iam really excited about using these volumes!

Had a question about the script found in the example scene "PT gradient dust occlusion"

Basically, what does this script do? It seems to dictate particle life based particle rotation but not sure as I am not very experienced in scripting. Hoping for someone to break down/explain the code-if anyone has time it would help very much. (particle event script)
-James.

set PT_vel =inParticle.velocity
set PT_rot =inParticle.rotation
PT_vel.NormalizeInPlace

set tmpVect1 = XSIMath.CreateVector3
set tmpVect2 = XSIMath.CreateVector3
set polyNormal = XSIMath.CreateVector3
set verticalVect = XSIMath.CreateVector3
set polyMatrix = XSIMath.CreateMatrix3
verticalVect.set PT_vel.x, PT_vel.y ,PT_vel.z
polyNormal.set 0,1,0

tmpVect1.cross polyNormal,verticalVect
tmpVect2.cross tmpVect1,polyNormal
tmpVect1.normalizeInPlace
tmpVect2.normalizeInPlace
polyNormal.normalizeInPlace
polyMatrix.set tmpVect1.x, tmpVect1.y, tmpVect1.z,_
polyNormal.x, polyNormal.y, polyNormal.z,_
tmpVect2.x, tmpVect2.y, tmpVect2.z

set rot =XSIMath.CreateRotation
rot.SetFromMatrix3 polyMatrix

rot.GetXYZAngles PT_rot
inParticle.rotation=PT_rot

[schoenberger]

It controls the orientation of the particle.
It is a "simple" up-vector script.
This way the particles are not rotating in every direction.
The rotation axis is parallel to the ground, the particles are "rolling" over the ground.
Just disable the event and you will see the difference in your shaded view.
_________________
Holger Schönberger
Binary Alchemy - digital materialization

[suntemple]

Holger,
thanks for explaining the script-makes sense now. I've had a bit more time to experiment with the shaders and I must say they are the best thing to happen to XSI particles. I have more questions but I ll post a new thread.
Thanks again,
James.