Behavior of skipIf precondition

[Vitaha]

According to the documentation https://www.behaviortree.dev/docs/guides/pre_post_conditions#example, precondition should behave exactly like the inverted condition, but in practice precondition is checked on every tick.

Difference between precondition and inverted condition

#include "behaviortree_cpp/bt_factory.h"

void RunTest(BT::Tree& tree)
{
  tree.rootBlackboard()->set("check", false);
  std::cout << toStr(tree.tickOnce()) << "\n";

  tree.rootBlackboard()->set("check", true);
  std::cout << toStr(tree.tickOnce()) << "\n";
  std::cout << toStr(tree.tickOnce()) << "\n";

  tree.rootBlackboard()->set("check", false);
  std::cout << toStr(tree.tickOnce()) << "\n";
}

static constexpr auto AlwaysCheckXML = R"(
<root BTCPP_format="4">
<BehaviorTree>
  <KeepRunningUntilFailure _skipIf="check == true">
    <AlwaysSuccess/>
  </KeepRunningUntilFailure>
</BehaviorTree>
</root>
)";

void TestAlwaysCheck()
{
  BT::BehaviorTreeFactory factory;
  auto tree = factory.createTreeFromText(AlwaysCheckXML);
  RunTest(tree);
}

// clang-format off

static constexpr auto SimpleCondition2XML = R"(
<root BTCPP_format="4">
<BehaviorTree>
  <Fallback>
    <IsCheckSet check="{check}"/>
    <KeepRunningUntilFailure>
      <AlwaysSuccess/>
    </KeepRunningUntilFailure>
  </Fallback>
</BehaviorTree>
</root>
)";

// clang-format on

void TestSimpleCondition2()
{
  BT::BehaviorTreeFactory factory;
  factory.registerSimpleCondition(
      "IsCheckSet",
      [](BT::TreeNode& node) {
        auto check = node.getInput<bool>("check").value();
        return check ? BT::NodeStatus::SUCCESS : BT::NodeStatus::FAILURE;
      },
      BT::PortsList{BT::InputPort("check")});

  auto tree = factory.createTreeFromText(SimpleCondition2XML);
  RunTest(tree);
}

int main()
{
  std::cout << "============= AlwaysCheck =============\n";
  TestAlwaysCheck();
  std::cout << "============= SimpleCondition =============\n";
  TestSimpleCondition2();

  return 0;
}

/* Expected output:

============= AlwaysCheck =============
RUNNING
SKIPPED
SKIPPED
RUNNING
============= SimpleCondition =============
RUNNING
RUNNING
RUNNING
RUNNING

*/

Also, when StatefulActionNode receives SKIPPED state on the first iteration, all subsequent ticks are skipped

Unexpected StatefulActionNode behavior

#include "behaviortree_cpp/bt_factory.h"

class MyTestNode : public BT::StatefulActionNode
{
public:
  MyTestNode(const std::string& name, const BT::NodeConfig& config) :
    BT::StatefulActionNode(name, config){};

  static BT::PortsList providedPorts()
  {
    return {};
  }

  BT::NodeStatus onStart() override
  {
    std::cout << "Node started\n";
    return BT::NodeStatus::RUNNING;
  }

  BT::NodeStatus onRunning() override
  {
    std::cout << "Node running\n";
    return BT::NodeStatus::RUNNING;
  }

  void onHalted() override
  {
    std::cout << "Node halted\n";
  }
};

void RunTest(BT::Tree& tree)
{
  tree.rootBlackboard()->set("check", false);
  std::cout << toStr(tree.tickOnce()) << "\n";

  tree.rootBlackboard()->set("check", true);
  std::cout << toStr(tree.tickOnce()) << "\n";
  std::cout << toStr(tree.tickOnce()) << "\n";

  tree.rootBlackboard()->set("check", false);
  std::cout << toStr(tree.tickOnce()) << "\n";
}

// clang-format off

static constexpr auto PreconditionXML = R"(
<root BTCPP_format="4">
<BehaviorTree>
  <MyTestNode _skipIf="check!=true"/>
</BehaviorTree>
</root>
)";

// clang-format on

void TestPrecondition()
{
  BT::BehaviorTreeFactory factory;
  factory.registerNodeType<MyTestNode>("MyTestNode");

  auto tree = factory.createTreeFromText(PreconditionXML);
  RunTest(tree);
}

// clang-format off

static constexpr auto SimpleConditionXML = R"(
<root BTCPP_format="4">
<BehaviorTree>
  <Fallback>
    <Inverter>
      <IsCheckSet check="{check}"/>
    </Inverter>
    <MyTestNode/>
  </Fallback>
</BehaviorTree>
</root>
)";

// clang-format on

void TestSimpleCondition()
{
  BT::BehaviorTreeFactory factory;
  factory.registerNodeType<MyTestNode>("MyTestNode");
  factory.registerSimpleCondition(
      "IsCheckSet",
      [](BT::TreeNode& node) {
        auto check = node.getInput<bool>("check").value();
        return check ? BT::NodeStatus::SUCCESS : BT::NodeStatus::FAILURE;
      },
      BT::PortsList{BT::InputPort("check")});

  auto tree = factory.createTreeFromText(SimpleConditionXML);
  RunTest(tree);
}

int main()
{
  std::cout << "============= Precondition =============\n";
  TestPrecondition();
  std::cout << "============= SimpleCondition =============\n";
  TestSimpleCondition();

  return 0;
}

/* Expected output:

============= Precondition =============
SKIPPED
SKIPPED
SKIPPED
SKIPPED
============= SimpleCondition =============
SUCCESS
Node started
RUNNING
Node running
RUNNING
Node running
RUNNING
Node halted

*/

[facontidavide]

Thanks for reporting, I will investigate

[facontidavide]

Fixed. thanks for reporting.

You can check the added unit tests:

https://github.com/BehaviorTree/BehaviorTree.CPP/blob/master/tests/gtest_preconditions.cpp#L229-L300