Help Constrain particles on axis

[josemendez]

Why the document combine transform and vector like (Transform target, Vector3 railDirection)?

I cannot add rigidbody to particles so that I add constrain on axis?

Hi,

That's simply a function with two input parameters. You should read more on how C# and programming in general works, as these are very basic issues.

You don't need to add a rigidbody component to particles, they already have a velocity.  In fact you could not add a component to them even if you wanted, as they are not GameObjects. You just need to use Vector3.Project on their velocity, that's it.