游戏AI角色的转向系统(Steering behaviors)实现
一些向量的接口是cocos2dx的。但从名字上应该能理解做了什么向量操作
Seek:
获取当前位置指向目标点的向量,转化为单位向量后再乘以速度值,即为所需速度desired velocity,所需速度减去当前速度current velocity,即为seek的转向力,将角色推向目标
//追逐转向力
Vec2 MoveNode::seek(Vec2 seekPos){if (seekPos == Vec2(-1, -1)) return Vec2::ZERO;Vec2 normalVector = (seekPos - this->getPosition()).getNormalized();float dist = this->getPosition().getDistance(seekPos);Vec2 desiredVelocity = normalVector * _dtSpeed;Vec2 steering;if (MoveSmooth) steering = desiredVelocity - _velocity;else steering = desiredVelocity;return steering;
}
物体在追逐目标时,会有一个逐渐转弯的过程
如果,没有转向力的话,物体就是直接切换方向
Flee
与seek类似,只是所需速度desired velocity的方向,是由目标点指向当前位置。
这里在逃离目标点加了个检测半径,在这个范围里的物体将会受到逃离力。
//躲避转向力
Vec2 MoveNode::flee() {Vec2 steering = Vec2::ZERO;if(_fleePos == Vec2::ZERO) return steering;if (this->getPosition().getDistance(_fleePos) < _fleeRadius) {Vec2 normalVector = (this->getPosition() - _fleePos).getNormalized();Vec2 desiredVelocity = normalVector * _dtSpeed;if (MoveSmooth) steering = desiredVelocity - _velocity;else steering = desiredVelocity;}return steering;
}
逃离时的转向效果
与没有转向力直接逃离的效果对比
arrive
因为seek力的存在,所以在到达目标点时,会在目标点附近来回弹跳
为此在目标点周围添加一个减速场slowing area。在目标点周围一定范围内,当物体越靠近目标时,seek力会越小。seek力大小在减速带范围内线性减小,与目标点的距离成反比。而在范围外,则是正常的seek力大小
//追逐转向力
Vec2 MoveNode::seek(Vec2 seekPos){if (seekPos == Vec2(-1, -1)) return Vec2::ZERO;Vec2 normalVector = (seekPos - this->getPosition()).getNormalized();float dist = this->getPosition().getDistance(seekPos);Vec2 desiredVelocity = normalVector * _dtSpeed;//靠近目标减速带if (dist < _tarSlowRadius) desiredVelocity *= (dist / _tarSlowRadius);Vec2 steering;if (MoveSmooth) steering = desiredVelocity - _velocity;else steering = desiredVelocity;return steering;
}
Wander
漫游:巡逻,在物体前进方向的前方一定范围_circleDistance内,画个圆,用来计算受力行为。位移力 以圆心为原点,受半径_circleRadius约束。半径越大以及角色到圆圈的距离越大,角色在每个游戏帧中受到的“推力”就越强。
初始会给一个方向wander angle,之后每帧会在一定的转向范围_changeAngle内随机一个转角方向。改变物体巡逻的方向wander angle
我在这里加了一个巡逻范围_wanderPullBackSteering,当偏离一定范围时,会受到回拉的力
Vec2 MoveNode::changeAngle(Vec2 vector, float angle) {float rad = angle * M_PI / 180;float len = vector.getLength();Vec2 v;v.x = len * cos(rad);v.y = len * sin(rad);return v;
}Vec2 MoveNode::wander() {if (_wanderPos == Vec2(-1, -1)) return Vec2::ZERO;Vec2 circleCenter = _velocity.getNormalized();circleCenter *= _circleDistance;Vec2 displacement = Vec2(0, -1);displacement *= _circleRadius;displacement = changeAngle(displacement, _wanderAngle);float randomValue = RandomHelper::random_real<float>(-0.5f, 0.5f);_wanderAngle = _wanderAngle + randomValue * _changeAngle;Vec2 wanderForce = circleCenter - displacement;float dist = this->getPosition().getDistance(_wanderPos);if (dist > _wanderRadius) {// 偏离漫游点一定范围的话,给个回头力Vec2 desiredVelocity = (_wanderPos - this->getPosition()).getNormalized() * _wanderPullBackSteering;desiredVelocity -= _velocity;wanderForce += desiredVelocity;}return wanderForce;
}
Pursuit
追捕某个物体,实际上就是seek到某个位置,只不过这个位置需要预测追捕目标将来的位置target in the future来seek,而不能以追捕目标当前位置来seek
预测的位置即目标当前位置+目标当前速度加一定帧数T。如果T的值是个常数时会出现一个问题:当目标很近时,追击精度往往会变差。这是因为当目标接近时,追击者会继续寻找目标位置的进行预测,也就是“远离”T帧后的位置。因此可以用动态T 值代替常量T 值
新的T值为目标从当前位置移动到追击者位置还需要更新多少次
Vec2 MoveNode::pursuit() {if (_pursuitObj == nullptr) return Vec2::ZERO;Vec2 pursuitPos = _pursuitObj->getPosition();float t = this->getPosition().getDistance(pursuitPos) / _dtSpeed;//float t = 3;Vec2 tarPos = pursuitPos + _pursuitObj->getVelocity() * t;//Vec2 tarPos = pursuitPos;return seek(tarPos);
}
没有预测的追捕的话,就会一直沿着追捕目标的路径一直跟在后面
Evading
躲避,与追捕类似,只不过将预测目标的位置用来做flee,而不是做seek
Combining Steering Forces
多种力是可以相互结合的,以向量的形式相加,得到物体最终受到的力
void MoveNode::update(float dt)
{_dtSpeed = _speed * dt;if (MoveSmooth) {Vec2 steering = Vec2::ZERO;steering += seek(_tarPos);steering += flee();steering += wander();steering += pursuit();steering = turncate(steering, _maxForce);steering *= ( 1 / (float)_mass );_velocity += steering;}else {_velocity += seek(_tarPos);_velocity += flee();_velocity += wander();_velocity += pursuit();}_velocity += wallAvoid();_velocity = turncate(_velocity, _maxSpeed * dt);updatePos();
}
下面是一个物体,受到多个正在漫游目标产生的逃离力的影响,同时还有寻求到目标的力 的例子
源码
MoveNode.h
#ifndef __MOVE_NODE_H__
#define __MOVE_NODE_H__#include "cocos2d.h"
USING_NS_CC;
using namespace std;class MoveNode : public Node
{
public:static MoveNode* create();CC_CONSTRUCTOR_ACCESS:virtual bool init() override;void setId(int id) { _id = id; };void setDirect(DrawNode* direct) { _direct = direct; };void setSpeed(float speed) { _speed = speed; };void setMaxForce(float maxForce) { _maxForce = maxForce; };void setMass(float mass) { _mass = mass; };void setMaxSpeed(float maxSpeed) { _maxSpeed = maxSpeed; };void setTarSlowRadius(float tarSlowRadius) { _tarSlowRadius = tarSlowRadius; };void setFleeRadius(float fleeRadius) { _fleeRadius = fleeRadius; };void setCircleDistance(float circleDistance) { _circleDistance = circleDistance; };void setCircleRadius(float circleRadius) { _circleRadius = circleRadius; };void setChangeAngle(float changeAngle) { _changeAngle = changeAngle; };void setWanderRadius(float wanderRadius) { _wanderRadius = wanderRadius; };void setWanderPullBackSteering(float wanderPullBackSteering) { _wanderPullBackSteering = wanderPullBackSteering; };void setPos(Vec2 pos);void setTarPos(Vec2 tarPos) { _tarPos = tarPos; };void setFleePos(Vec2 fleePos) { _fleePos = fleePos; };void setFleeObjs(vector<MoveNode*> fleeObjs) { _fleeObjs = fleeObjs; };void setWanderPos(Vec2 wanderPos);void switchPursuitObj(MoveNode* pursuitObj);Vec2 seek(Vec2 seekPos);Vec2 flee();Vec2 wander();Vec2 pursuit();Vec2 wallAvoid();Vec2 turncate(Vec2 vector, float maxNumber);Vec2 changeAngle(Vec2 vector, float angle);void updatePos();void update(float dt);int getId() { return _id; };Vec2 getVelocity(){ return _velocity; };void setVelocity(Vec2 velocity) { _velocity = velocity; };
protected:DrawNode* _direct;int _id;float _speed; //速度float _maxForce; //最大转向力,即最大加速度float _mass; //质量float _maxSpeed; //最大速度float _tarSlowRadius; //抵达目标减速半径float _fleeRadius; //逃离目标范围半径float _circleDistance; //巡逻前方圆点距离float _circleRadius; //巡逻前方圆半径float _changeAngle; //巡逻转向最大角度float _wanderRadius; //巡逻点范围半径float _wanderPullBackSteering; //超出巡逻范围拉回力float _dtSpeed; //每帧速度值Vec2 _velocity; //速度float _wanderAngle; //巡逻角度Vec2 _wanderPos; //巡逻范围中心点Vec2 _tarPos; //目标点Vec2 _fleePos; //逃离点MoveNode* _pursuitObj; //追逐目标vector<MoveNode*> _fleeObjs; //逃离目标float wallAvoidRadius = 50.0f; //墙壁碰撞检测半径
};#endif
MoveNode.cpp
#include "MoveNode.h"bool MoveSmooth = true;MoveNode* MoveNode::create() {MoveNode* moveNode = new(nothrow) MoveNode();if (moveNode && moveNode->init()) {moveNode->autorelease();return moveNode;}CC_SAFE_DELETE(moveNode);return nullptr;
}bool MoveNode::init()
{_tarPos = Vec2(-1, -1);_wanderPos = Vec2(-1, -1);_velocity.setZero();_pursuitObj = nullptr;this->scheduleUpdate();return true;
}void MoveNode::update(float dt)
{_dtSpeed = _speed * dt;if (MoveSmooth) {Vec2 steering = Vec2::ZERO;steering += seek(_tarPos);steering += flee();steering += wander();steering += pursuit();steering = turncate(steering, _maxForce);steering *= ( 1 / (float)_mass );_velocity += steering;}else {_velocity += seek(_tarPos);_velocity += flee();_velocity += wander();_velocity += pursuit();}_velocity += wallAvoid();_velocity = turncate(_velocity, _maxSpeed * dt);updatePos();
}Vec2 MoveNode::wallAvoid() {Vec2 temp = _velocity.getNormalized();temp *= wallAvoidRadius;Vec2 tarPos = this->getPosition() + temp;if (!Rect(Vec2::ZERO, Director::getInstance()->getVisibleSize()).containsPoint(tarPos)) {Vec2 steering = Vec2::ZERO;if (tarPos.y >= Director::getInstance()->getVisibleSize().height) steering += Vec2(0, -1);if (tarPos.y <= 0) steering += Vec2(0, 1);if (tarPos.x >= Director::getInstance()->getVisibleSize().width) steering += Vec2(-1, 0);if (tarPos.x <= 0) steering += Vec2(1, 0);return steering * _dtSpeed;}return Vec2::ZERO;
}void MoveNode::updatePos() {Vec2 tarPos = this->getPosition() + _velocity;if (!Rect(Vec2::ZERO, Director::getInstance()->getVisibleSize()).containsPoint(tarPos)) {_velocity = _velocity *= -100;}Vec2 directPos = _velocity.getNormalized() *= 5;_direct->setPosition(directPos);this->setPosition(tarPos);if (_velocity == Vec2::ZERO) _tarPos = Vec2(-1, -1);
}Vec2 MoveNode::turncate(Vec2 vector, float maxNumber) {if (vector.getLength() > maxNumber) { vector.normalize();vector *= maxNumber;}return vector;
}//追逐转向力
Vec2 MoveNode::seek(Vec2 seekPos){if (seekPos == Vec2(-1, -1)) return Vec2::ZERO;Vec2 normalVector = (seekPos - this->getPosition()).getNormalized();float dist = this->getPosition().getDistance(seekPos);Vec2 desiredVelocity = normalVector * _dtSpeed;//靠近目标减速带if (dist < _tarSlowRadius) desiredVelocity *= (dist / _tarSlowRadius);Vec2 steering;if (MoveSmooth) steering = desiredVelocity - _velocity;else steering = desiredVelocity;return steering;
}//躲避转向力
Vec2 MoveNode::flee() {Vec2 steering = Vec2::ZERO;if (!_fleeObjs.empty()) {for (auto eludeObj : _fleeObjs) {auto fleePos = eludeObj->getPosition();if (fleePos.getDistance(this->getPosition()) < _fleeRadius) {Vec2 normalVector = (this->getPosition() - fleePos).getNormalized();Vec2 desiredVelocity = normalVector * _dtSpeed;Vec2 steeringChild;if (MoveSmooth) steeringChild = desiredVelocity - _velocity;else steeringChild = desiredVelocity;steering += steeringChild;}}return steering;}if(_fleePos == Vec2::ZERO) return steering;if (this->getPosition().getDistance(_fleePos) < _fleeRadius) {Vec2 normalVector = (this->getPosition() - _fleePos).getNormalized();Vec2 desiredVelocity = normalVector * _dtSpeed;if (MoveSmooth) steering = desiredVelocity - _velocity;else steering = desiredVelocity;}return steering;
}Vec2 MoveNode::changeAngle(Vec2 vector, float angle) {float rad = angle * M_PI / 180;float len = vector.getLength();Vec2 v;v.x = len * cos(rad);v.y = len * sin(rad);return v;
}Vec2 MoveNode::wander() {if (_wanderPos == Vec2(-1, -1)) return Vec2::ZERO;Vec2 circleCenter = _velocity.getNormalized();circleCenter *= _circleDistance;Vec2 displacement = Vec2(0, -1);displacement *= _circleRadius;displacement = changeAngle(displacement, _wanderAngle);float randomValue = RandomHelper::random_real<float>(-0.5f, 0.5f);_wanderAngle = _wanderAngle + randomValue * _changeAngle;Vec2 wanderForce = circleCenter - displacement;float dist = this->getPosition().getDistance(_wanderPos);if (dist > _wanderRadius) {// 偏离漫游点一定范围的话,给个回头力Vec2 desiredVelocity = (_wanderPos - this->getPosition()).getNormalized() * _wanderPullBackSteering;desiredVelocity -= _velocity;wanderForce += desiredVelocity;}return wanderForce;
}Vec2 MoveNode::pursuit() {if (_pursuitObj == nullptr) return Vec2::ZERO;Vec2 pursuitPos = _pursuitObj->getPosition();float t = this->getPosition().getDistance(pursuitPos) / _dtSpeed;//float t = 3;
// Vec2 tarPos = pursuitPos + _pursuitObj->getVelocity() * t;Vec2 tarPos = pursuitPos;return seek(tarPos);
}void MoveNode::setPos(Vec2 pos) {this->setPosition(pos);_velocity.setZero();
}void MoveNode::setWanderPos(Vec2 wanderPos) {_wanderPos = wanderPos;setPos(wanderPos);
}void MoveNode::switchPursuitObj(MoveNode* pursuitObj) {if (_pursuitObj == nullptr) _pursuitObj = pursuitObj;else {_pursuitObj = nullptr;_velocity = Vec2::ZERO;_tarPos = Vec2(-1, -1);}
}