Task 3: Nested arbitration graphs

Integrate a long-term behavior and add another layer to the arbitration graph.

Context

We have now implemented a behavior component and integrated it into the arbitration graph. So far, all behavior components are children of the root arbitrator.

Let’s make things a bit more interesting by adding a long-term behavior component that’s also about eating dots. The ChangeDotCluster behavior will move Pac-man to an area in the maze where there is a higher density of dots.

For now, we’ll just decide between the two dot eating strategies using chance. We can achieve that by adding them to a random arbitrator which is then added as an option to the root arbitrator.

There are more sophisticated ways to decide between behavior components, we’ll cover those in the next task.

Goal

Add the EatClosestDot and ChangeDotCluster behavior components to a random arbitrator nested within the root arbitrator.

Instructions

• Add the ChangeDotCluster behavior component as a new member of the PacmanAgent class and initialize it in the constructor.
• Add a random arbitrator as a new member of the PacmanAgent class, analogous to the priority arbitrator.
• Add the EatClosestDot and ChangeDotCluster behavior components as options to the random arbitrator.
• Add the random arbitrator as an option to the root arbitrator.
• Run the game and observe how Pac-Man behaves.

Solution

Click here to expand the solution

Include the header of the ChangeDotCluster behavior component and the random arbitrator in include/demo/pacman_agent.hpp:

#include <arbitration_graphs/random_arbitrator.hpp>

#include "change_dot_cluster_behavior.hpp"

For better code readability, add the following alias near the top of the class definition:

using RandomArbitrator = arbitration_graphs::RandomArbitrator<Command, Command>;

Add the ChangeDotCluster behavior component and the RandomArbitrator as a new members of the PacmanAgent class:

private:
    ChangeDotClusterBehavior::Ptr changeDotClusterBehavior_;

    RandomArbitrator::Ptr eatDotsArbitrator_;

In the constructor of the PacmanAgent class, initialize the ChangeDotCluster behavior component and the RandomArbitrator: Add the EatClosestDot and ChangeDotCluster behavior components as options to the random arbitrator. Finally, add the random arbitrator as an option to the root arbitrator:

explicit PacmanAgent(const entt::Game& game)
        : parameters_{}, environmentModel_{std::make_shared<EnvironmentModel>(game)} {

    avoidGhostBehavior_ = std::make_shared<AvoidGhostBehavior>(environmentModel_, parameters_.avoidGhostBehavior);
    // Initialize the ChangeDotCluster behavior component
    changeDotClusterBehavior_ = std::make_shared<ChangeDotClusterBehavior>(environmentModel_);
    chaseGhostBehavior_ = std::make_shared<ChaseGhostBehavior>(environmentModel_, parameters_.chaseGhostBehavior);
    eatClosestDotBehavior_ = std::make_shared<EatClosestDotBehavior>(environmentModel_);
    moveRandomlyBehavior_ = std::make_shared<MoveRandomlyBehavior>(parameters_.moveRandomlyBehavior);

    // Initialize the random arbitrator and add the EatClosestDot and ChangeDotCluster behavior components as options
    eatDotsArbitrator_ = std::make_shared<RandomArbitrator>("EatDots");
    eatDotsArbitrator_->addOption( changeDotClusterBehavior_, RandomArbitrator::Option::Flags::INTERRUPTABLE);
    eatDotsArbitrator_->addOption( eatClosestDotBehavior_, RandomArbitrator::Option::Flags::INTERRUPTABLE);

    rootArbitrator_ = std::make_shared<PriorityArbitrator>("Pacman");
    rootArbitrator_->addOption(chaseGhostBehavior_, PriorityArbitrator::Option::Flags::INTERRUPTABLE);
    rootArbitrator_->addOption(avoidGhostBehavior_, PriorityArbitrator::Option::Flags::INTERRUPTABLE);
    // The EatDot arbitrator is itself an option of the root arbitrator
    rootArbitrator_->addOption(eatDotsArbitrator_, PriorityArbitrator::Option::Flags::INTERRUPTABLE);
    rootArbitrator_->addOption(moveRandomlyBehavior_, PriorityArbitrator::Option::Flags::INTERRUPTABLE);
}

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