在游戏中,场景里存在大量的物体.如果我们把所有物体的变化都广播给玩家.那客户端很难承受这么大的压力.因此我们肯定会做优化.把不必要的信息过滤掉.如只关心玩家视野所看到的.减轻客户端的压力,给玩家更流畅的体验.

        优化的思路一般是: 第一个是尽量降低向客户端同步对象的数量,第二个是尽量降低单个对象向客户端同步的数据.

       "九宫格"是最常见的视野管理算法了.它的优点在于原理和实现都非常简单.

        

// AOI 管理器
type AOIManager interface {
	GetWidth() int
	GetHeight() int
	OnEnter(obj scene.GameObject, enterPos *geom.Vector2d) bool
	OnLeave(obj scene.GameObject) bool
	OnMove(obj scene.GameObject, movePos *geom.Vector2d) bool
	OnSync()
}

一 . 定义管理器接口:

1. 进入区域  2. 离开区域  3. 在区域移动 4. 同步信息

具体实现:

type TowerAOIManager struct {
	minX, maxX, minY, maxY float64 // 单位 m
	towerRange             float64 // 格子大小
	towers                 [][]tower
	xTowerNum, yTowerNum   int
}

划分格子: 按照实际情况出发,规定格子大小 towerRange. (一般 九个格子的范围需大于屏幕看到的视野范围) 这样才能保证客户端场景物体的生成和消失在玩家屏幕外.不会突然出现.

// 构造结构
func NewTowerAOIManager(minX, maxX, minY, maxY float64, towerRange float64) AOIManager {
	mgr := &TowerAOIManager{minX: minX, maxX: maxX, minY: minY, maxY: maxY, towerRange: towerRange}
	mgr.init()
	return mgr
}

func (m *TowerAOIManager) init() {
	numXSlots := int((m.maxX-m.minX)/m.towerRange) + 1
	m.xTowerNum = numXSlots
	numYSlots := int((m.maxY-m.minY)/m.towerRange) + 1
	m.yTowerNum = numYSlots
	m.towers = make([][]tower, numXSlots)
	for i := 0; i < numXSlots; i++ {
		m.towers[i] = make([]tower, numYSlots)
		for j := 0; j < numYSlots; j++ {
			key := NewKey(int64(i), int64(j))
			m.towers[i][j].init(int64(key))
		}
	}

}

二 . 定义区域 tower : 

type tower struct {
	towerId       int64
	context       *TowerSyncContext
	mapId2Obj     map[uint32]scene.GameObject // obj容器
	mapId2Watcher map[uint32]scene.GameObject // 观察集合
}

func (t *tower) init(key int64) {
	t.towerId = key
	t.context = NewTowerSyncContext() // 同步信息
	t.mapId2Obj = make(map[uint32]scene.GameObject)
	t.mapId2Watcher = make(map[uint32]scene.GameObject)
}

func (t *tower) AddObj(obj scene.GameObject, fromOtherTower scene.AOITower, bExclude bool) {
	obj.SetAOITower(t)

	t.mapId2Obj[obj.GetId()] = obj
	if fromOtherTower == nil {
		for watcherId, watcher := range t.mapId2Watcher {
			if bExclude && watcherId == obj.GetId() {
				continue
			}

			watcher.OnEnterAOI(obj)
		}

	} else {
		// obj moved from other tower to this tower
		for watcherId, watcher := range fromOtherTower.GetWatchers() {
			if watcherId == obj.GetId() {
				continue
			}

			if _, ok := t.mapId2Watcher[watcherId]; ok {
				continue
			}

			watcher.OnLeaveAOI(obj)
		}

		for watcherId, watcher := range t.mapId2Watcher {
			if watcherId == obj.GetId() {
				continue
			}

			if _, ok := fromOtherTower.GetWatchers()[watcherId]; ok {
				continue
			}

			watcher.OnEnterAOI(obj)
		}
	}
}

func (t *tower) RemoveObj(obj scene.GameObject, notifyWatchers bool) {
	obj.SetAOITower(nil)
	delete(t.mapId2Obj, obj.GetId())
	if notifyWatchers {
		for watcherId, watcher := range t.mapId2Watcher {
			if watcherId == obj.GetId() {
				continue
			}

			watcher.OnLeaveAOI(obj)
		}
	}
}

func (t *tower) addWatcher(obj scene.GameObject, bExclude bool) {
	if bExclude {
		if _, ok := t.mapId2Watcher[obj.GetId()]; ok {
			// todo log
			return
		}
	}

	t.mapId2Watcher[obj.GetId()] = obj
	// now obj can see all objs under this tower
	for neighborId, neighbor := range t.mapId2Obj {
		if neighborId == obj.GetId() {
			continue
		}

		obj.OnEnterAOI(neighbor)
	}
}

func (t *tower) removeWatcher(obj scene.GameObject) {
	if _, ok := t.mapId2Watcher[obj.GetId()]; !ok {
		// todo log
		return
	}

	delete(t.mapId2Watcher, obj.GetId())
	for neighborId, neighbor := range t.mapId2Obj {
		if neighborId == obj.GetId() {
			continue
		}

		obj.OnLeaveAOI(neighbor)
	}
}

func (t *tower) GetWatchers() map[uint32]scene.GameObject {
	return t.mapId2Watcher
}

func (t *tower) GetObjs() map[uint32]scene.GameObject {
	return t.mapId2Obj
}

func (t *tower) GetTowerId() int64 {
	return t.towerId
}

func (t *tower) AddSyncData(mod uint16, cmd uint16, msg protoreflect.ProtoMessage) {
	t.context.AddSyncData(mod, cmd, msg)
}

func (t *tower) Broadcast() {
	if len(t.context.fights) == 0 {
		return
	}

	// 广播协议
	 ....   
    
	t.context.ClearContext()
}

三. AOI 的具体方法实现

我们在回过头来继续说 mgr 的方法.

1.  进入实现: 

前提:

GameObject : 一切场景物体的基础接口 

type GameObject interface {}

Vector2d : X,Y 坐标

type Vector2d struct {
	x, y, w float64
}

具体实现: 

如果是从上一个区域内离开,则先走 离开上一个区域,然后计算当前进入位置坐标对应的九宫区域,

然后把obj 加入到各个区域内

func (m *TowerAOIManager) OnEnter(obj scene.GameObject, enterPos *geom.Vector2d) bool {
	if obj.GetAOITower() != nil {
		m.OnLeave(obj) // 离开上一个区域
	}

	obj.SetPosition(enterPos) // 设置当前位置
    // obj 视野范围内的所有区域
	m.visitWatchedTowers(enterPos, obj.GetViewRange(), func(tower *tower) {
		tower.addWatcher(obj, false)
	})

	t := m.getTowerXY(enterPos)
    // 当前位置所在的区域
	t.AddObj(obj, nil, false)

	return true
}

func (m *TowerAOIManager) getTowerXY(xyPos *geom.Vector2d) *tower {
	xi, yi := m.transXY(xyPos.GetX(), xyPos.GetY())
	return &m.towers[xi][yi]
}

关键的方法:

        计算obj当前位置中,视野内能被观察到的所有区域.

func (m *TowerAOIManager) visitWatchedTowers(xyPos *geom.Vector2d, aoiDistance float64, f func(*tower)) {
	ximin, ximax, yimin, yimax := m.getWatchedTowers(xyPos.GetX(), xyPos.GetY(), aoiDistance)
	for xi := ximin; xi <= ximax; xi++ {
		for yi := yimin; yi <= yimax; yi++ {
			tower := &m.towers[xi][yi]
			f(tower)
		}
	}
}

func (aoiman *TowerAOIManager) getWatchedTowers(x, y float64, aoiDistance float64) (int, int, int, int) {
	ximin, yimin := aoiman.transXY(x-aoiDistance, y-aoiDistance)
	ximax, yimax := aoiman.transXY(x+aoiDistance, y+aoiDistance)
	return ximin, ximax, yimin, yimax
}

func (m *TowerAOIManager) transXY(x, y float64) (int, int) {
	xi := int((x - m.minX) / m.towerRange)
	yi := int((y - m.minY) / m.towerRange)
	return m.normalizeXi(xi), m.normalizeYi(yi)
}

func (m *TowerAOIManager) normalizeXi(xi int) int {
	if xi < 0 {
		xi = 0
	} else if xi >= m.xTowerNum {
		xi = m.xTowerNum - 1
	}
	return xi
}

func (m *TowerAOIManager) normalizeYi(yi int) int {
	if yi < 0 {
		yi = 0
	} else if yi >= m.yTowerNum {
		yi = m.yTowerNum - 1
	}
	return yi
}

2. 离开区域:

        

func (m *TowerAOIManager) OnLeave(obj scene.GameObject) bool {
	obj.GetAOITower().RemoveObj(obj, true) // 离开当前区域

    // 查找视野内所有区域,然后从关注列表中移除
	m.visitWatchedTowers(obj.GetPosition(), obj.GetViewRange(), func(tower *tower) {
		tower.removeWatcher(obj)
	})

	return true
}

3. 移动

       每帧移动坐标点 movePos

func (m *TowerAOIManager) OnMove(obj scene.GameObject, movePos *geom.Vector2d) bool {
	oldX, oldY := obj.GetPosition().GetX(), obj.GetPosition().GetY()
	obj.SetPosition(movePos) //设置当前坐标

	t0 := obj.GetAOITower()
	t1 := m.getTowerXY(movePos)

    // 判断移动是否跨区域了
	if t0.GetTowerId() != t1.GetTowerId() {
		t0.RemoveObj(obj, false)
		t1.AddObj(obj, t0, true)
	}

    // 计算前后变化的区域,进行移除和添加关注列表
	oximin, oximax, oyimin, oyimax := m.getWatchedTowers(oldX, oldY, obj.GetViewRange())
	ximin, ximax, yimin, yimax := m.getWatchedTowers(movePos.GetX(), movePos.GetY(), obj.GetViewRange())

	for xi := oximin; xi <= oximax; xi++ {
		for yi := oyimin; yi <= oyimax; yi++ {
			if xi >= ximin && xi <= ximax && yi >= yimin && yi <= yimax {
				continue
			}

			tower := &m.towers[xi][yi]
			tower.removeWatcher(obj)
		}
	}

	for xi := ximin; xi <= ximax; xi++ {
		for yi := yimin; yi <= yimax; yi++ {
			if xi >= oximin && xi <= oximax && yi >= oyimin && yi <= oyimax {
				continue
			}

			tower := &m.towers[xi][yi]
			tower.addWatcher(obj, true)
		}
	}

	return true
}

 4 . 同步

       每帧同步所有区域变化的物体对象

func (m *TowerAOIManager) OnSync() {
	for i := 0; i < m.xTowerNum; i++ {
		for j := 0; j < m.yTowerNum; j++ {
			m.towers[i][j].Broadcast()
		}
	}
}

 简单的实现了 AOI 区域变化管理,当然后面还需要优化,我们知道"九宫格" 算法的缺点:

1 . 当玩家跨越格子的时候,比如说从A点到B点.瞬间会有新增格子,那其中的对象就会进入视野,与此同时,就会有消失的格子,那其中的对象就要消失视野.这个瞬间就会出现一个流量激增点,它可能会导致客户端卡顿等问题.

2. 流量浪费.有客户端不需要的对象被同步过来了.我们知道它是基于格子来管理地图对象的.那么就会无法保证九宫区域一定刚好是视野范围.肯定是大于视野区域这样才保证同步对象正确.(如果是俯视角那种 ,视野就会是一个 梯形范围.)

 或者你可以在服务端中,根据客户端梯形视野在作一遍初筛.

        如果你有更好的优化方案,欢迎留言交流!