In this seventh step we will focus on the display and more specifically the aspects of the agents: how they are represented. It can be a simple shape (circle, square, etc.), an icon, a polygon (see later GIS support).
We add a new variable of type file called my_icon to the generic_species. We define as well two new aspects:
species generic_species {
...
file my_icon;
...
aspect base {
draw circle(size) color: color ;
}
aspect icon {
draw my_icon size: 2 * size ;
}
aspect info {
draw square(size) color: color ;
draw string(energy with_precision 2) size: 3 color: #black ;
}
}
We specialize the prey species from the generic_species species:
species prey parent: generic_species {
...
file my_icon <- file("../images/predator_prey_sheep.png") ;
...
}
The image file is here: 
You have to copy it in your project folder: images/
As done for the prey species, we specialize the predator species from the generic_species species:
species predator parent: generic_species {
...
file my_icon <- file("../images/predator_prey_wolf.png") ;
...
}
The image file is here: 
You have to copy it in your project folder: images
We change the default aspect of the prey and predator agents to icon aspect.
output {
display main_display {
grid vegetation_cell lines: #black ;
species prey aspect: icon ;
species predator aspect: icon ;
}
}
We define a new display called info_display that displays the prey and predator agents with the info aspect.
output {
display info_display {
species prey aspect: info;
species predator aspect: info;
}
}
model prey_predator
global {
int nb_preys_init <- 200;
int nb_predators_init <- 20;
float prey_max_energy <- 1.0;
float prey_max_transfert <- 0.1 ;
float prey_energy_consum <- 0.05;
float predator_max_energy <- 1.0;
float predator_energy_transfert <- 0.5;
float predator_energy_consum <- 0.02;
float prey_proba_reproduce <- 0.01;
int prey_nb_max_offsprings <- 5;
float prey_energy_reproduce <- 0.5;
float predator_proba_reproduce <- 0.01;
int predator_nb_max_offsprings <- 3;
float predator_energy_reproduce <- 0.5;
int nb_preys -> {length (prey)};
int nb_predators -> {length (predator)};
init {
create prey number: nb_preys_init ;
create predator number: nb_predators_init ;
}
}
species generic_species {
float size <- 1.0;
rgb color ;
float max_energy;
float max_transfert;
float energy_consum;
float proba_reproduce ;
float nb_max_offsprings;
float energy_reproduce;
file my_icon;
vegetation_cell myCell <- one_of (vegetation_cell) ;
float energy <- (rnd(1000) / 1000) * max_energy update: energy - energy_consum max: max_energy ;
init {
location <- myCell.location;
}
reflex basic_move {
myCell <- one_of (myCell.neighbours) ;
location <- myCell.location ;
}
reflex die when: energy <= 0 {
do die ;
}
reflex reproduce when: (energy >= energy_reproduce) and (flip(proba_reproduce)) {
int nb_offsprings <- 1 + rnd(nb_max_offsprings -1);
create species(self) number: nb_offsprings {
myCell <- myself.myCell ;
location <- myCell.location ;
energy <- myself.energy / nb_offsprings ;
}
energy <- energy / nb_offsprings ;
}
aspect base {
draw circle(size) color: color ;
}
aspect icon {
draw my_icon size: 2 * size ;
}
aspect info {
draw square(size) color: color ;
draw string(energy with_precision 2) size: 3 color: #black ;
}
}
species prey parent: generic_species {
rgb color <- #blue;
float max_energy <- prey_max_energy ;
float max_transfert <- prey_max_transfert ;
float energy_consum <- prey_energy_consum ;
float proba_reproduce <- prey_proba_reproduce ;
int nb_max_offsprings <- prey_nb_max_offsprings ;
float energy_reproduce <- prey_energy_reproduce ;
file my_icon <- file("../images/predator_prey_sheep.png") ;
reflex eat when: myCell.food > 0 {
float energy_transfert <- min([max_transfert, myCell.food]) ;
myCell.food <- myCell.food - energy_transfert ;
energy <- energy + energy_transfert ;
}
}
species predator parent: generic_species {
rgb color <- #red ;
float max_energy <- predator_max_energy ;
float energy_transfert <- predator_energy_transfert ;
float energy_consum <- predator_energy_consum ;
list<prey> reachable_preys update: prey inside (myCell);
float proba_reproduce <- predator_proba_reproduce ;
int nb_max_offsprings <- predator_nb_max_offsprings ;
float energy_reproduce <- predator_energy_reproduce ;
file my_icon <- file("../images/predator_prey_wolf.png") ;
reflex eat when: ! empty(reachable_preys) {
ask one_of (reachable_preys) {
do die ;
}
energy <- energy + energy_transfert ;
}
}
grid vegetation_cell width: 50 height: 50 neighbours: 4 {
float maxFood <- 1.0 ;
float foodProd <- (rnd(1000) / 1000) * 0.01 ;
float food <- (rnd(1000) / 1000) max: maxFood update: food + foodProd ;
rgb color <- rgb(int(255 * (1 - food)), 255, int(255 * (1 - food))) update: rgb(int(255 * (1 - food)), 255, int(255 *(1 - food))) ;
list<vegetation_cell> neighbours <- (self neighbours_at 2);
}
experiment prey_predator type: gui {
parameter "Initial number of preys: " var: nb_preys_init min: 0 max: 1000 category: "Prey" ;
parameter "Prey max energy: " var: prey_max_energy category: "Prey" ;
parameter "Prey max transfert: " var: prey_max_transfert category: "Prey" ;
parameter "Prey energy consumption: " var: prey_energy_consum category: "Prey" ;
parameter "Initial number of predators: " var: nb_predators_init min: 0 max: 200 category: "Predator" ;
parameter "Predator max energy: " var: predator_max_energy category: "Predator" ;
parameter "Predator energy transfert: " var: predator_energy_transfert category: "Predator" ;
parameter "Predator energy consumption: " var: predator_energy_consum category: "Predator" ;
parameter 'Prey probability reproduce: ' var: prey_proba_reproduce category: 'Prey' ;
parameter 'Prey nb max offsprings: ' var: prey_nb_max_offsprings category: 'Prey' ;
parameter 'Prey energy reproduce: ' var: prey_energy_reproduce category: 'Prey' ;
parameter 'Predator probability reproduce: ' var: predator_proba_reproduce category: 'Predator' ;
parameter 'Predator nb max offsprings: ' var: predator_nb_max_offsprings category: 'Predator' ;
parameter 'Predator energy reproduce: ' var: predator_energy_reproduce category: 'Predator' ;
output {
display main_display {
grid vegetation_cell lines: #black ;
species prey aspect: icon ;
species predator aspect: icon ;
}
display info_display {
grid vegetation_cell lines: #black ;
species prey aspect: info ;
species predator aspect: info ;
}
monitor "Number of preys" value: nb_preys;
monitor "Number of predators" value: nb_predators;
}
}