This tutorial will go through how to get started with parameter managers. It will start with an overly simple project to highlight some key features, then, apply the same parameter management to a more advanced project.

The first project is a simple “newRGG” type project. It will be composed of shoots (cylinders) and buds (spheres). The single growth rule replace a bud by a shoot and two buds.

We consider 2 types of bud that will make the growth slightly different: a green one, and a blue one. They both extend the same base bud module.

We first declare the three type of modules that will represent the possible type of “bud”.

module BaseBud(super.radius) extends Sphere {
	int age = 0;
	void grow(){
		switch(aging){
			case 0: 
				age+=1;
				break;
			case 1:
				age = (age>1)? age*age : (age>0)? 2 : 1;
				break;
			default:
		}
	}
}
 
module GBud(super.radius) extends BaseBud.(setShader(GREEN)) {
	void grow(){
		super.grow();
		radius *= 0.8;
	}
}
module BBud(super.radius) extends BaseBud.(setShader(BLUE)) {
	void grow(){
		super.grow();
		radius *= 0.6;
	}
}

Then we define some variables that represent the configuration of the project:

• aging : the type of aging 0 or 1, it trigger the method declared in BaseBud
• ageLimit : the threshold after which a bud cannot be replaced anymore (I know that's not how plant works but it is an example - could be any type of variable)
• budType : 0 or 1 for green of blue bud
• initialLength : the initial length of the shoot.

public global int aging = 0;
public global int ageLimit = 10;
public global int budType = 0;
public global float initialLength = 0.8;

Then, we can declare a Bud factory, i.e. a method that produce the type of bud based on the budType:

BaseBud pBud(float len) { 
	switch (budType) {
		case 0:
			return new GBud(len); 
		case 1:
			return new BBud(len); 
		default:
		return null;
	}
}

Lastly, the initialization and growth rule:

protected void init ()
[
	Axiom ==>  pBud(initialLength);
]
 
public void run ()
[
	b:BaseBud(x), (!tooOld(b)) ==> F(x) [RU(30) RH(90) pBud(b[radius]).($[age]=b[age], grow())] 
					  [RU(-30) RH(90) pBud(b[radius]).($[age]=b[age], grow())];
]

The given model can be run until the ageLimit threshold is met. Depending on the value of each of the four presented variables, the resulting “tree” is different.

We can first tag these fours variables as parameters to change them from the GUI editor.

Replace their previous declaration with:

@IsParameter
@Choice({"Linear", "Exponential"})
public global int aging = 0;
 
@IsParameter
public global int ageLimit = 10;
 
@IsParameter
@Choice({"Green bud", "Blue bud"})
public global int budType = 0;
 
@Range(min=0, max=1)
@IsParameter
public global float initialLength = 0.8;

Now open the GUI editor by clicking on the parameter manager button:

It will open the editor:

In order to simulate how these parameters could impact the resulting tree (not only from a 3d view perspective) we can compute a simple descriptor: the total volume of the buds with the method:

public void compute_vol() {
	double s = sum( (*Sphere*).getVolume() );
	println("Total volume of buds: " + s);
}
 
public void complete(){
	for (applyUntilFinished()){
		run();
	}
	compute_vol();
}

Now we can also set up the project to be run-able in headless and modify parameters from outside of GroIMP, with either:

• Command lines args
• Modify the parameter file