Martin Kraus: Direct Manipulation of Parametrized Graphics
  Parametrized Graphics

  An example with reassignments of INDEPENDENT_VARIABLES:
  
<HTML>
<APPLET 
  ARCHIVE="live.jar" 
  CODE="Live.class" 
  WIDTH=400 HEIGHT=400>
<PARAM 
  NAME="INDEPENDENT_VARIABLES"
  VALUE="{x->1,y->0}">
<PARAM 
  NAME="DEPENDENT_VARIABLES"
  VALUE="{phi->ArcTan[x,y],
    x->Cos[phi],
    y->Sin[phi]}">
<PARAM 
  NAME="INPUT"
  VALUE="Graphics3D[
    {Line[{{0,0,0},{x,y,0}}],
    PointSize[0.08],
    Point[{x,y,0}]},
    PlotRange->{{-1,1},
    {-1,1},{-0.1,0.1}]">
</APPLET>
</HTML>