Copy/Paste the following code to your GroIMP project:
//**********************************************************
/*
You will learn with this example:
– how to create a simple model of shoot growth with alternating
positioning of lateral branches.
*/

// definition of a terminal bud as extension of a sphere
module B(float len, float w) extends Sphere(0.1)
{{setShader(GREEN);}}

// definition of a lateral bud as extension of a sphere
module LB(float len) extends Sphere(0.1)
{{setShader(GREEN);}}

// definition of an internode as extension of the module F
module I(float len) extends F(len);

// start method with the axiom (generates a bud)
protected void init()
[
Axiom ==> B(1, 30);
]

// Block which can be executed interactively.
// It appears in the menu.
// The block contains two rules, one for each type of bud.

public void run()
[
// multiplication of the angle by -1
// is responsible for the alternating positions

B(x, w) ==> I(x) [ RU(w) RH(90) LB(0.3*x) ] B(0.95*x, -w);

LB(x) ==> I(x) LB(x);

]

//**********************************************************