Generate Entities at Run-Time

There are two options for generating entities during run-time:

  1. Make use of the generate_rate, generate_count, generate_start_time, and generate_time_variance XML tags defined in Mission XML Tag Definitions.

  2. Create a plugin that publishes the scrimmage_msgs::GenerateEntity message on the “GenerateEntity” topic.

This document describes how to accomplish the second option.

Mission File Setup

The first step is to create a valid entity block in your mission XML file with an entity tag and a count of zero. For example, the start of the following entity block has a tag of “gen_straight” and a count of zero, which prevents it from being generated at the start of the simulation.

<!-- Entity that is generated during runtime by other plugins -->
<entity tag="gen_straight">

Create the GenerateEntity Message

The second step is to publish a scrimmage_msgs::GenerateEntity message on the “GenerateEntity” topic (GlobalNetwork) in a plugin (any type of plugin).

Your plugin should include the appropriate protobuf header files:

#include <scrimmage/pubsub/Publisher.h>
#include <scrimmage/proto/State.pb.h>
#include <scrimmage/msgs/Event.pb.h>
#include <scrimmage/proto/ProtoConversions.h>

In the plugin’s init() function, create the publisher:

// PublisherPtr pub_gen_ents_; is declared in the header file
pub_gen_ents_ = advertise("GlobalNetwork", "GenerateEntity");

When you want to generate an entity during the simulation, you refer to the entity’s XML tag and create a state for this entity when constructing the GenerateEntity message.

// Create a state for the entity and place it at position (10, 10, 100) with
// a roll, pitch, and yaw of (0 deg, 45 deg, 45 deg).
State s;
s.pos() << 10, 10, 100;
s.quat() = scrimmage::Quaternion(0, M_PI / 4.0, M_PI / 4.0);

// Create the GenerateEntity message
auto msg = std::make_shared<Message<scrimmage_msgs::GenerateEntity>>();

// Copy the new state into the message
sc::set(msg->data.mutable_state(), s);

// Set the entity_tag that references the entity to be generated in the
// mission XML file.

// Publish the GenerateEntity message

Modify Entity Block Properties

Before publishing the message, you can modify other properties of the entity block, such as the autonomy, color, health, visual_model, etc., by adding an entity block key-value pair to the GenerateEntity message:

// Modify the entity's color
auto kv_color = msg->data.add_entity_param();
kv_color->set_value("255, 255, 0");

// Modify the entity's visual model
auto kv_visual = msg->data.add_entity_param();

// Publish the GenerateEntity message

Modify Plugin Parameters

Currently, this entity generation interface doesn’t allow you to modify the XML attributes of specific plugins. If you need to generate entities with different plugin parameters you can either use multiple entity blocks with different entity tags or you can create new plugin XML files that have differently configured default parameters. For example, you could copy and rename the Straight.xml file to MyStraight.xml and then modify the plugin parameters in MyStraight.xml. In your entity, you can load the MyStraight autonomy plugin by referencing it directly as long as it is in your SCRIMMAGE_PLUGIN_PATH:

<entity tag="gen_my_straight">

In your entity generation plugin, you can modify the autonomy tag before publishing the GenerateEntity message:

auto kv_autonomy = msg->data.add_entity_param();
kv_autonomy->set_value("MyStraight2"); // Load parameters from MyStraight2.xml