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内建SwitchNode的局限?
BT6：ControlNodes源码解析 - 知乎
https://zhuanlan.zhihu.com/p/472996050
BehaviorTree.CPP中有内建的SwitchNode，定义在 BehaviorTree.CPP/include/behaviortree_cpp_v3/controls/switch_node.h。但是其只能接收string类型的值，因为定义的input port就是string类型。
static PortsList providedPorts() {
PortsList ports;
ports.insert(BT::InputPort<std::string>("variable"));
for (unsigned i = 0; i < NUM_CASES; i++) {
char case_str[20];
sprintf(case_str, "case_%d", i + 1);
ports.insert(BT::InputPort<std::string>(case_str));
}
return ports;
}这样用起来很不方便，大多数switch-case的逻辑都是和枚举值一起用的。因此我实现了一个自定义的control node，用来接收枚举类型的值，称为EnumSwitchNode。改动很简单，只需将input port的类型改为模板，并检查输入类是枚举类型。
Talk is cheap, let's see the code.
自定义的EnumSwitchNode
#ifndef BTNODES_CONTROL_NODES_ENUM_SWITCH_NODE_H
#define BTNODES_CONTROL_NODES_ENUM_SWITCH_NODE_H
#include "behaviortree_cpp_v3/control_node.h"
namespace BT {
/**
* @brief BehaviorTree.CPP的SwitchNode只能输入string类型的值
* 这里添加可以输入枚举类型的值
*/
template <size_t NUM_CASES, typename T>
class EnumSwitchNode : public ControlNode {
public:
EnumSwitchNode(const std::string& name, const BT::NodeConfiguration& config)
: ControlNode::ControlNode(name, config), running_child_(-1) {}
virtual ~EnumSwitchNode() override = default;
void halt() override {
running_child_ = -1;
ControlNode::halt();
}
static PortsList providedPorts() {
PortsList ports;
ports.insert(BT::InputPort<T>("enum_variable"));
for (unsigned i = 0; i < NUM_CASES; i++) {
char case_str[20];
sprintf(case_str, "case_%d", i + 1);
ports.insert(BT::InputPort<std::string>(case_str));
}
return ports;
}
private:
int running_child_;
virtual BT::NodeStatus tick() override;
};
template <size_t NUM_CASES, typename T>
inline NodeStatus EnumSwitchNode<NUM_CASES, T>::tick() {
// 如果是非枚举类型，会编译报错
static_assert(std::is_enum<T>::value,
"[registerNode]: accepts only enum classes!!!");
constexpr const char* case_port_names[9] = {"case_1", "case_2", "case_3",
"case_4", "case_5", "case_6",
"case_7", "case_8", "case_9"};
if (childrenCount() != NUM_CASES + 1) {
throw LogicError(
"Wrong number of children in EnumSwitchNode; "
"must be (num_cases + default)");
}
T variable, value;
int child_index = NUM_CASES; // default index;
if (getInput("enum_variable", variable)) {
// check each case until you find a match
for (unsigned index = 0; index < NUM_CASES; ++index) {
bool found = false;
if (index < 9) {
found = (bool)getInput(case_port_names[index], value);
} else {
char case_str[20];
sprintf(case_str, "case_%d", index + 1);
found = (bool)getInput(case_str, value);
}
if (found && variable == value) {
child_index = index;
break;
}
}
}
// if another one was running earlier, halt it
if (running_child_ != -1 && running_child_ != child_index) {
haltChild(running_child_);
}
auto& selected_child = children_nodes_[child_index];
NodeStatus ret = selected_child->executeTick();
if (ret == NodeStatus::RUNNING) {
running_child_ = child_index;
} else {
haltChildren();
running_child_ = -1;
}
return ret;
}
} // namespace BT
#endif // BTNODES_CONTROL_NODES_ENUM_SWITCH_NODE_H应用示例
// 宠物类型
enum class PetType : uint8_t {
UNDEFINED = 0,
DOG,
CAT,
BIRD,
};我们创建1个枚举类-宠物类型PetType，并实现由string向PetType转换的函数convertFromString()，它将会在读取xml中port值时自动调用。
template <>
inline PetType BT::convertFromString(BT::StringView key) {
auto parts = BT::splitString(key, ',');
if (parts.size() != 1) {
throw BT::RuntimeError("invalid input");
} else {
auto str = parts[0];
if ("PetType::UNDEFINED" == str) {
return PetType::UNDEFINED;
} else if ("PetType::DOG" == str) {
return PetType::DOG;
} else if ("PetType::CAT" == str) {
return PetType::CAT;
} else if ("PetType::BIRD" == str) {
return PetType::BIRD;
} else {
throw BT::RuntimeError(std::string("invalid input, chars=") +
str.to_string());
}
}
}创建1个简单的行为树，第1个SetBlackboard节点负责向{my_pet} entry写入枚举值，第2个SwitchNode负责根据读到的值，执行对应的分支来打印。?
<root main_tree_to_execute = "MainTree" >
<BehaviorTree ID="MainTree">
<Sequence>
<!-- 改变my_pet的值，可以运行不同的case -->
<SetBlackboard output_key="my_pet" value="PetType::DOG"/>
<EnumSwitch3_PetType enum_variable="{my_pet}" case_1="PetType::DOG" case_2="PetType::CAT" case_3="PetType::BIRD">
<Action ID="SaySomething" name="dog_say" message="wang...wang..."/>
<Action ID="SaySomething" name="cat_say" message="miao...miao..."/>
<Action ID="SaySomething" name="bird_say" message="bugu...bugu..."/>
<Action ID="SaySomething" name="default_be_quiet" message="xu..."/>
</EnumSwitch3_PetType>
</Sequence>
</BehaviorTree>
</root>main()中，需要向factory注册用到的2种node: SaySomething和EnumSwitchNode，这里指定了其接受的枚举类型，还可以同时创建多个不同的EnumSwitchNode。
int main() {
BT::BehaviorTreeFactory factory;
factory.registerNodeType<SaySomething>("SaySomething");
// 注册要使用的枚举类switch node
factory.registerNodeType<BT::EnumSwitchNode<3, PetType>>(
"EnumSwitch3_PetType");
auto tree = factory.createTreeFromText(xml_text);
tree.tickRoot();
return 0;
}SaySomething node就是读取message port值并打印。
class SaySomething : public BT::SyncActionNode {
public:
SaySomething(const std::string& name, const BT::NodeConfiguration& config)
: BT::SyncActionNode(name, config) {}
// You must override the virtual function tick()
BT::NodeStatus tick() override {
auto msg = getInput<std::string>("message");
if (!msg) {
throw BT::RuntimeError("missing required input [message]: ", msg.error());
}
std::cout << "SaySomething::tick()- " << msg.value() << std::endl;
return BT::NodeStatus::SUCCESS;
}
// It is mandatory to define this static method.
static BT::PortsList providedPorts() {
return {BT::InputPort<std::string>("message")};
}
};直接运行，会得到如下结果。大家可以改变{my_pet} entry的值来观察输出的变化。
SaySomething::tick()- wang...wang...