add t19

examples/CMakeLists.txt

@@ -42,6 +42,7 @@ endif()
 
 CompileExample("t17_blackboard_backup")
 CompileExample("t18_waypoints")
+CompileExample("t19_global_blackboard")
 
 CompileExample("ex01_wrap_legacy")
 CompileExample("ex02_runtime_ports")

examples/t19_global_blackboard.cpp

@@ -0,0 +1,111 @@
+#include "behaviortree_cpp/bt_factory.h"
+
+using namespace BT;
+
+/**
+ * This example introduces the concept of a "global blackboard",
+ * and the syntax to use it.
+ *
+ * As you know know from previous tutorials, blackboard are "scoped",
+ * i.e. each SubTree (including the one in the root) has its own
+ * Blackboard, isolated by default, unless we do remapping.
+ *
+ * It is possible (since version 4.6) to create a global BB,
+ * accessible from everywhere without remapping.
+ *
+ * In the example below we can access the entry "value" and
+ * "value_sqr" from everywhere, as long as we use the pregix "@".
+ *
+ * Note as <SubTree ID="MySub"/> doesn't have any remapping
+ *
+ * In other words, the prefix "@" means: "search the entry in the top-level
+ * blackboard of the hierarchy".
+ *
+ * In this case, the top-level blackboard will be [global_blackboard].
+ */
+
+// clang-format off
+static const char* xml_main = R"(
+<root BTCPP_format="4">
+
+  <BehaviorTree ID="MainTree">
+    <Sequence>
+      <PrintNumber name="main_print" val="{@value}" />
+      <SubTree ID="MySub"/>
+    </Sequence>
+  </BehaviorTree>
+
+  <BehaviorTree ID="MySub">
+    <Sequence>
+      <PrintNumber name="sub_print" val="{@value}" />
+      <Script code="@value_sqr := @value * @value" />
+    </Sequence>
+  </BehaviorTree>
+</root>
+ )";
+
+// clang-format on
+
+class PrintNumber : public BT::SyncActionNode
+{
+public:
+  PrintNumber(const std::string& name, const BT::NodeConfig& config)
+    : BT::SyncActionNode(name, config)
+  {}
+
+  // You must override the virtual function tick()
+  NodeStatus tick() override
+  {
+    const int val = getInput<int>("val").value();
+    std::cout << "[" << name() << "] val: " << val << std::endl;
+    return NodeStatus::SUCCESS;
+  }
+
+  // It is mandatory to define this static method.
+  static BT::PortsList providedPorts()
+  {
+    return { BT::InputPort<int>("val") };
+  }
+};
+
+//---------------------------------------------------
+int main()
+{
+  BehaviorTreeFactory factory;
+
+  factory.registerNodeType<PrintNumber>("PrintNumber");
+  factory.registerBehaviorTreeFromText(xml_main);
+
+  // No one "own" this blackboard
+  auto global_blackboard = BT::Blackboard::create();
+  // This blackboard will be owned by "MainTree". It parent is global_blackboard
+  auto root_blackboard = BT::Blackboard::create(global_blackboard);
+
+  auto tree = factory.createTree("MainTree", root_blackboard);
+
+  for(int i = 1; i <= 3; i++)
+  {
+    global_blackboard->set("value", i);
+    tree.tickOnce();
+    int value_sqr = global_blackboard->get<int>("value_sqr");
+    std::cout << "[While loop] value: " << i << " value_sqr: " << value_sqr << "\n\n";
+  }
+
+  return 0;
+}
+
+/* Expecte output:
+
+[main_print] val: 1
+[sub_print] val: 1
+[While loop] value: 1 value_sqr: 1
+
+[main_print] val: 2
+[sub_print] val: 2
+[While loop] value: 2 value_sqr: 4
+
+[main_print] val: 3
+[sub_print] val: 3
+[While loop] value: 3 value_sqr: 9
+
+*/