t02_basic_ports.cpp

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#include "behaviortree_cpp/bt_factory.h"
 
#include "dummy_nodes.h"
 
using namespace BT;
 
// clang-format off
static const char* xml_text = R"(
 
 <root BTCPP_format="4" >
 
     <BehaviorTree ID="MainTree">
        <Sequence name="root">
            <SaySomething     message="hello" />
            <SaySomething2    message="this works too" />
            <ThinkWhatToSay   text="{the_answer}"/>
            <SaySomething2    message="{the_answer}" />
        </Sequence>
     </BehaviorTree>
 
 </root>
 )";
// clang-format on
 
class ThinkWhatToSay : public BT::SyncActionNode
{
public:
  ThinkWhatToSay(const std::string& name, const BT::NodeConfig& config)
    : BT::SyncActionNode(name, config)
  {}
 
  // This Action simply write a value in the port "text"
  BT::NodeStatus tick() override
  {
    setOutput("text", "The answer is 42");
    return BT::NodeStatus::SUCCESS;
  }
 
  // A node having ports MUST implement this STATIC method
  static BT::PortsList providedPorts()
  {
    return { BT::OutputPort<std::string>("text") };
  }
};
 
int main()
{
  using namespace DummyNodes;
 
  BehaviorTreeFactory factory;
 
  // The class SaySomething has a method called providedPorts() that define the INPUTS.
  // In this case, it requires an input called "message"
  factory.registerNodeType<SaySomething>("SaySomething");
 
  // Similarly to SaySomething, ThinkWhatToSay has an OUTPUT port called "text"
  // Both these ports are std::string, therefore they can connect to each other
  factory.registerNodeType<ThinkWhatToSay>("ThinkWhatToSay");
 
  // SimpleActionNodes can not define their own method providedPorts(), therefore
  // we have to pass the PortsList explicitly if we want the Action to use getInput()
  // or setOutput();
  PortsList say_something_ports = { InputPort<std::string>("message") };
  factory.registerSimpleAction("SaySomething2", SaySomethingSimple, say_something_ports);
 
  /* An INPUT can be either a string, for instance:
     *
     *     <SaySomething message="hello" />
     *
     * or contain a "pointer" to a type erased entry in the Blackboard,
     * using this syntax: {name_of_entry}. Example:
     *
     *     <SaySomething message="{the_answer}" />
     */
 
  auto tree = factory.createTreeFromText(xml_text);
 
  tree.tickWhileRunning();
 
  /*  Expected output:
     *
        Robot says: hello
        Robot says: this works too
        Robot says: The answer is 42
    *
    * The way we "connect" output ports to input ports is to "point" to the same
    * Blackboard entry.
    *
    * This means that ThinkSomething will write into the entry with key "the_answer";
    * SaySomething and SaySomething will read the message from the same entry.
    *
    */
  return 0;
}