DrawParametricCurve.rvb

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' DrawParametricCurve.rvb -- February 2007
' If this code works, it was written by Dale Fugier.
' If not, I don't know who wrote it.
' Works with Rhino 4.0.
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Option Explicit

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' Subroutine: DrawParametricCurve
' Purpose:    Create a interpolated curve based on a parametric equation.
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Sub DrawParametricCurve()
  Dim t0, t1, t, intCount, x, arrPoint, arrPoints()
  Dim a, b
  a = 6
  b = 3

  ' Get the minimum parameter
  t0 = Rhino.GetReal("Minimum t value", 0.0)
  If IsNull(t0) Then Exit Sub

  ' Get the maximum parameter
  t1 = Rhino.GetReal("Maximum t value", 1.0)
  If IsNull(t1) Then Exit Sub

  ' Get the number of sampling points to interpolate through
  intCount = Rhino.GetInteger("Number of points", 50, 2)
  If IsNull(intCount) Then Exit Sub

  ' Get the first point
  ReDim arrPoints(intCount - 1)
  arrPoint = CalculatePoint(t0, a, b)
  arrPoints(0) = arrPoint

  ' Get the rest of the points
  For x = 1 To intCount - 2
    t = (1.0 - (x / intCount) ) * t0 + (x / intCount) * t1
    arrPoint = CalculatePoint(t, a, b)
    arrPoints(x) = arrPoint
  Next

  ' Get the last point
  arrPoint = CalculatePoint(t1, a, b)
  arrPoints(intCount - 1) = arrPoint

  ' Add the curve

  Rhino.AddInterpCurve arrPoints

End Sub

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' Function:   CalculatePoint
' Purpose:    Customizable function that solves a parametric equation.
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Function CalculatePoint(t)
  Dim arrPoint(2)
  If IsNumeric(t) Then
    arrPoint(0) = (4 * (1 - t) + 1 * t) * Sin(3 * 6.2832 * t)
    arrPoint(1) = (4 * (1 - t) + 1 * t) * Cos(3 * 6.2832 * t)
    arrPoint(2) = 5 * t
    CalculatePoint = arrPoint
  Else
    CalculatePoint = Null
  End If
End Function