/* You learn at this example:

- how the thickness growth according to the "pipe model"
  can be modelled more elegantly with the relation
  "minDescendants".
  
-minDescendants-> yields in the graph the next successor
having the subsequently specified node type and skips
nodes of other types. Successor and branch edges are
taken into account.

Growth in length and growth in thickness are again separated.
It is no longer necessary to use the sequential mode of
rule application, thanks to the -minDescendants-> relation.

*/

module B extends Sphere(0.4)
{{ setShader(GREEN);}};

module C extends Sphere(0.5)
{{ setShader(RED);}};

module S(super.diameter) extends F(10, diameter, 2);

module T(super.diameter) extends F(10, diameter, 14);
  // marked shoot: supposed to propagate its diameter downwards

float D0 = 0.001;  // initial shoot diameter (nearly 0)
float D1 = 1.0;    // final diameter of distal shoots

protected void init()
[ Axiom ==> S(D0) B; ]

public void grow_l()         // length growth of the structure
[
B ==> [ RU(35) S(D0) B ] [ RU(-35) S(D0) B ];
]

public void grow_d()         
[
S(d) B ==> T(D1) C;   // marking of distal shoots

s:S(d), (empty((* S(y) -ancestor-> s *))) ==> t:T(0),
   {
   float dd = 0.0;
   for ((* s -minDescendants-> T(y) *)) // searches marked 
                                        // successors
      dd = Math.sqrt(dd*dd + y*y);  // pipe model!
   t[diameter] = Math.max(t[diameter], dd); // no shrinking
   };
]