Option Explicit
'Script written by Luis Gil
'Script copyrighted by www.legil.org

Call offsetSrfs

Sub offsetSrfs

Dim arrSrfs
arrSrfs = Rhino.GetObjects("Select surfaces", 8, , True)
If IsNull(arrSrfs) Then Exit Sub
  
Rhino.AddLayer "OffsetSrf", RGB(255, 0, 150)

Dim i
Call Rhino.EnableRedraw(False)
For i = LBound(arrSrfs) To UBound(arrSrfs)
  Dim arrPc, arrCentroid
  arrPc = Rhino.SurfaceAreaCentroid(arrSrfs(i))
  arrCentroid = arrPc(0)
  
  Dim strNewSrf
  strNewSrf = Rhino.ScaleObject(arrSrfs(i), arrCentroid, Array(0.8, 0.8, 0.8), True)
  
  Rhino.ObjectLayer strNewSrf, "OffsetSrf"
  
  Dim arrPh1 : arrPh1 = Array(arrSrfs(i))
  Dim arrPh2 : arrPh2 = Array(strNewsrf)
  
  Rhino.BooleanDifference arrPh1, arrPh2
  
Next
Call Rhino.EnableRedraw(True)

End Sub