ParticlesFollowSurface

from pymel.core import *
sl = selected()
scatterAmnt = 1000
SurfaceOffsetAnmt = .01
SurfaceForce = -1
ParticleSize = .1
UniformDistribution = True
currentTime(1, u=1)
for s in sl:
    name = s
    if UniformDistribution:
        ScatterNode = ls(name+"_mesh2arrays") # will chech to see if node exsists already
        if ScatterNode:# if node does not exsist
            delete(ScatterNode)
        ScatterNode = createNode("mesh2arrays") # create node
        rename(ScatterNode, name+"_mesh2arrays")
        ScatterNode = ls(name+"_mesh2arrays") #this is dumb, but finds node again after renaming
        s.worldMesh[0] >> ScatterNode[0].inputMesh # connections
        setAttr(name+"_mesh2arrays"+".type",3)
        setAttr(name+"_mesh2arrays"+".count",scatterAmnt)
        setAttr(name+"_mesh2arrays"+".relaxIterations",20)
        ScatterArray = getAttr(ScatterNode[0].positionArray)
        ScatterNormalArray = getAttr(ScatterNode[0].normalArray)
        ScatterArrayOffset = []
        i=0
        for pos in ScatterArray:# offset particle from surface
            newPos = pos + ScatterNormalArray[i]*SurfaceOffsetAnmt
            ScatterArrayOffset.append(newPos)
            i+=1


    ParticleCheck = ls(name+"_surfaceParticles")
    if ParticleCheck:
        delete(ParticleCheck)
    ParticleScatter = particle(p = ScatterArrayOffset, jr=1, n= name+"_surfaceParticles")
    setAttr(ParticleScatter[0] +".particleRenderType", 4)
    addAttr(ParticleScatter[1], ln="radius", at="float", min= 0, max = 10, dv = ParticleSize)
    setAttr(ParticleScatter[0] +".goalSmoothness", 10)
    setAttr(ParticleScatter[0] +".visibleInReflections", 1)
    setAttr(ParticleScatter[0] +".visibleInRefractions", 1)
    setAttr(ParticleScatter[0] +".lifespanMode", 3)
    NewAttrList = "RandomScale","RandomIndex","collisionU","collisionV","goalU","goalV","traceDepthPP","randomRotationX","rotationPP"
    for attr in NewAttrList:
        addAttr(ParticleScatter, ln=attr,dt="doubleArray")
    goal(ParticleScatter,g= s, w=1)
    addAttr(ParticleScatter, ln="userVector1PP" ,dt="vectorArray")
    collision(s,ParticleScatter[0], r=0, f=1, o =.01)
    connectDynamic(ParticleScatter[0], c=s)
    # expression
    p = str(ParticleScatter[1])
    ex = "{0}.goalPP = 0;".format(ParticleScatter[1])
    ex += "\n"+p+".randomRotationX = rand(360);"
    ex += "\n"+p+".userVector1PP = <<0,1,0>>;"
    ex += "\n"+p+".RandomIndex = rand(0,3);"
    ex += "\n"+p+".RandomScale = rand(.9,1.1);"
    dynExpression(ParticleScatter[1], c=1, s = ex)
    exAD = "vector $normal = <<0,rand(0,360),0>>;"+"\n"
    exAD += "float $rotZ = rad_to_deg((atan2(($normal.y),($normal.x))));"+"\n"
    exAD +="float $rotY = rad_to_deg((asin(-($normal.z))));"+"\n"
    exAD += ""+p+".rotationPP = <<"+p+".randomRotationX,$rotY,$rotZ>>;"
    exBD = "if("+p+".collisionU > -1)"+"\n"+"{"+"\n"+""+p+".goalPP=1;"+"\n"+""+p+".goalU = "+p+".collisionU;"+"\n"+""+p+".goalV = "+p+".collisionV;"+"\n"+""+p+".traceDepthPP=0;"+"\n"+"}"
    exBD +="if(frame > 5 && "+p+".goalU == 0){"+p+".lifespanPP = 0;}"
    dynExpression(ParticleScatter[1], rbd=1, s = exBD)
    for i in range(0,scatterAmnt-1): # shoot the particle back at surface
        particle(ParticleScatter[1], at="velocity", id=i, vv = ScatterNormalArray[i]*SurfaceForce, e=1)