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Version: 4.4

Introduction to the Scripting language

A more detailed description can be found at Introduction to Scripting. This tutorial provides a very basic example that you can use as an initial playground.

Script and Precondition nodes

In our scripting language, variables are entries in the blackboard.

In this example, we use the node Script to set these variables and observe as we can access them as input ports in SaySomething.

The types being supported are numbers (integers and reals), strings and registered ENUMS.


Note that we use magic_enums that has some known limitations.

A notable one is that the default range is [-128, 128], unless changes as described in the link above.

We will use this XML:

<root BTCPP_format="4">
<Script code=" msg:='hello world' " />
<Script code=" A:=THE_ANSWER; B:=3.14; color:=RED " />
<Precondition if="A>B && color != BLUE" else="FAILURE">
<SaySomething message="{A}"/>
<SaySomething message="{B}"/>
<SaySomething message="{msg}"/>
<SaySomething message="{color}"/>

We expected the following blackboard entries to contain:

  • msg: the string "hello world"
  • A: the integer value corresponding to the alias THE_ANSWER.
  • B: the real value 3.14
  • C: the integer value corresponding to the enum RED.

The expected output is, therefore:

Robot says: 42.000000
Robot says: 3.140000
Robot says: hello world
Robot says: 1.000000

The C++ code is:

enum Color
RED = 1,
BLUE = 2,

int main()
BehaviorTreeFactory factory;

// We can add these enums to the scripting language.
// Check the limits of magic_enum

// Or we can manually assign a number to the label "THE_ANSWER".
// This is not affected by any range limitation
factory.registerScriptingEnum("THE_ANSWER", 42);

auto tree = factory.createTreeFromText(xml_text);

return 0;