Unity NavMesh 动态烘焙
最初的Unity导航系统很不完善，只能静态烘焙场景图的可行走区域，而且必须在本地保存场景的NavMesh数据，难以运行时动态计算；这使得鲜有开发者愿意再尝试Unity内置的导航功能，转向了AStar寻路算法的研究。但实际上AStar算法真的适合大多数开发情况且性能较优么？
了解过AStar算法的都知道，它是基于格子来遍历计算行走权重的，算法复杂度其实是相对较高的，受到格子密度，地图大小和路线长度的的影响较大。
AStar更适合的是策略性寻路，该算法更有利于找出最短路径的最优解，能够达到足够的精确性。
而Unity的NavMesh是用的拐角点算法，随便找一个场景烘焙一下便可得知，例如：
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烘焙出来的NavMesh区域只在障碍物边缘与平面边缘存在顶点，而不会像AStar一样均匀的布满整个平面；如果是一个无任何障碍物的平面，那就只会有平面边缘的几个顶点，算法效率是相对较高的，并不会因为地图变大而有明显算法复杂度上的变化。
相反，NavMesh的缺点也正是AStar的优点，那就是难以保证寻路的最优解，更多的时候是用于AI能够更快计算出绕过障碍物朝向目标前进的路径。
对于场景不变的静态地图来说，Unity最初的NavMesh已经能够满足需求，但如果地图随机生成或障碍物的位置随时变化，此时静态NavMesh一下子就捉襟见肘了。
好在随着Unity版本的更新，关于动态烘焙的方法也已经能有效实现，这样无论是以怎样千变万化的方式生成的随机地图，随机地图在游戏中如何构建重组，都能动态刷新出NavMesh的可行走区域。
using UnityEngine;using UnityEngine.AI;using System.Collections.Generic;// Tagging component for use with the LocalNavMeshBuilder// Supports mesh-filter and terrain - can be extended to physics and/or primitivespublic class NavMeshSourceTag : MonoBehaviour{ // Global containers for all active mesh/terrain tags public static List<MeshFilter> m_Meshes = new List<MeshFilter>(); public static List<Terrain> m_Terrains = new List<Terrain>(); void OnEnable() { var m = GetComponent<MeshFilter>(); if (m != null) { m_Meshes.Add(m); } var t = GetComponent<Terrain>(); if (t != null) { m_Terrains.Add(t); } } void OnDisable() { var m = GetComponent<MeshFilter>(); if (m != null) { m_Meshes.Remove(m); } var t = GetComponent<Terrain>(); if (t != null) { m_Terrains.Remove(t); } } // Collect all the navmesh build sources for enabled objects tagged by this component public static void Collect(ref List<NavMeshBuildSource> sources) { sources.Clear(); for (var i = 0; i < m_Meshes.Count; ++i) { var mf = m_Meshes; if (mf == null) continue; var m = mf.sharedMesh; if (m == null) continue; var s = new NavMeshBuildSource(); s.shape = NavMeshBuildSourceShape.Mesh; s.sourceObject = m; s.transform = mf.transform.localToWorldMatrix; s.area = 0; sources.Add(s); } for (var i = 0; i < m_Terrains.Count; ++i) { var t = m_Terrains; if (t == null) continue; var s = new NavMeshBuildSource(); s.shape = NavMeshBuildSourceShape.Terrain; s.sourceObject = t.terrainData; // Terrain system only supports translation - so we pass translation only to back-end s.transform = Matrix4x4.TRS(t.transform.position, Quaternion.identity, Vector3.one); s.area = 0; sources.Add(s); } }}
NavMeshSourceTag类是为了收集需要录入烘焙列表的模型网格数据和地形数据，用的是一个全局的静态数据列表来存储，需要挂载在场景的网格物件上，标记哪些物件的网格在生成数据时需要考虑在内。
当然了，如果一个物体是由多个网格拼接而成，读者只需要将OnEnable和OnDisable中的代码稍作修改，改为读取子物体中的所以MeshFilter和Terrain组件即可：
foreach (var m in GetComponentsInChildren<MeshFilter>()) { if (m != null) { m_Meshes.Add(m); } }
将之前收集到的网格物件的源数据动态烘焙刷新生成NavMesh：
using UnityEngine;using UnityEngine.AI;using System.Collections;using System.Collections.Generic;using NavMeshBuilder = UnityEngine.AI.NavMeshBuilder;// Build and update a localized navmesh from the sources marked by NavMeshSourceTagpublic class LocalNavMeshBuilder : MonoBehaviour{ // The center of the build public Transform m_Tracked; // The size of the build bounds public Vector3 m_Size = new Vector3(80.0f, 20.0f, 80.0f); NavMeshData m_NavMesh; AsyncOperation m_Operation; NavMeshDataInstance m_Instance; List<NavMeshBuildSource> m_Sources = new List<NavMeshBuildSource>(); IEnumerator Start() { while (true) { UpdateNavMesh(true); yield return m_Operation; } } void OnEnable() { Bake(); } void OnDisable() { //Unload navmesh and clear handle m_Instance.Remove(); } /// <summary> /// 按范围动态更新NavMesh /// </summary> /// <param name="asyncUpdate">是否异步加载</param> void UpdateNavMesh(bool asyncUpdate = false) { NavMeshSourceTag.Collect(ref m_Sources); var defaultBuildSettings = NavMesh.GetSettingsByID(0); var bounds = QuantizedBounds(); if (asyncUpdate) m_Operation = NavMeshBuilder.UpdateNavMeshDataAsync(m_NavMesh, defaultBuildSettings, m_Sources, bounds); else NavMeshBuilder.UpdateNavMeshData(m_NavMesh, defaultBuildSettings, m_Sources, bounds); } static Vector3 Quantize(Vector3 v, Vector3 quant) { float x = quant.x * Mathf.Floor(v.x / quant.x); float y = quant.y * Mathf.Floor(v.y / quant.y); float z = quant.z * Mathf.Floor(v.z / quant.z); return new Vector3(x, y, z); } Bounds QuantizedBounds() { // Quantize the bounds to update only when theres a 0.1% change in size var center = m_Tracked ? m_Tracked.position : transform.position; return new Bounds(Quantize(center, .001f * m_Size), m_Size); } //选择物体时在Scene中绘制Bound区域 void OnDrawGizmosSelected() { if (m_NavMesh) { Gizmos.color = Color.green; Gizmos.DrawWireCube(m_NavMesh.sourceBounds.center, m_NavMesh.sourceBounds.size); } Gizmos.color = Color.yellow; var bounds = QuantizedBounds(); Gizmos.DrawWireCube(bounds.center, bounds.size); Gizmos.color = Color.green; var center = m_Tracked ? m_Tracked.position : transform.position; Gizmos.DrawWireCube(center, m_Size); } //动态烘焙NavMesh public void Bake() { // Construct and add navmesh m_NavMesh = new NavMeshData(); m_Instance = NavMesh.AddNavMeshData(m_NavMesh); if (m_Tracked == null) m_Tracked = transform; UpdateNavMesh(false); }}
有一个地方需要注意，因为NavMeshBuilder.UpdateNavMeshData(m_NavMesh, defaultBuildSettings, m_Sources, bounds); 刷新NavMeshData时需要读取模型的网格信息，此时需要将导入的模型读写打开，设置位置如下：
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用法示例：
using UnityEngine;public class LocalNavMeshCtrl : MonoBehaviour{ public LocalNavMeshBuilder Bulider; public float Offse; void Awake() { EventManager.AddListener<EnterRoomEvent>(EnterRoomHanlder); } private void EnterRoomHanlder(EnterRoomEvent e) { if (Bulider != null) { var rooms = BattleUtils.MapMgr.Rooms; if (rooms.ContainsKey(e.RoomIndex) && rooms.RoomType == RoomType.Battle) { Bulider.m_Tracked = rooms.transform; var size = PTBattleMgr.CurRoomCtrl.Size; Bulider.m_Size = new Vector3(size.x * 4 + Offse, 10, size.y * 4 + Offse); } } } private void OnDestroy() { EventManager.RemoveListener<EnterRoomEvent>(EnterRoomHanlder); }}
例如进入某一房间或区域就按照该房间区域的大小进行NavMesh的动态烘焙，可以非常方便的改变烘焙的范围和中心点等，也可以考虑让该烘焙范围一直跟随玩家的Transform运动。
一个区域内的NavMesh动态烘焙完成后，很多AI可能需要在NavMesh中取随机点进行导航的目标点的设置或巡逻等，可以写一个扩展方法得到NavMesh的顶点数据，取任何一个三角内的点即可：
public static Vector3 GetNavMeshRandomPos(this GameObject obj) { NavMeshTriangulation navMeshData = NavMesh.CalculateTriangulation(); int t = Random.Range(0, navMeshData.indices.Length - 3); Vector3 point = Vector3.Lerp(navMeshData.vertices], navMeshData.vertices], Random.value); point = Vector3.Lerp(point, navMeshData.vertices], Random.value); return point; }
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