//hit中就包含了法线和碰撞点
RaycastHit hit = this.GetHitInfoOnWater (worldPoint);
float waterLevel = hit.point.y;//从水面上方垂直向下发射射线，得到和水面的交点public RaycastHit GetHitInfoOnWater (Vector3 worldPoint) {Vector3 _originUP = worldPoint + Vector3.up * 1000;Ray _rayDown = new Ray (_originUP, Vector3.down);RaycastHit hit;if (Physics.Raycast (_rayDown, out hit, Mathf.Infinity,1<<LayerMask.NameToLayer("Water"))) {return hit;}return hit;}

==============================RiverInstance.cs==============================
public class RiverSegInfo {public float LengthRadio;public float halfWidth;public Vector3 flowDir;public Vector3 center;
}
================================River.cs========================================
//记录河流宽度信息
m_riverSegmentInfos.Add (new RiverSegInfo () {LengthRadio = (float) i / _resultWayPoints.Count,//当前位置所处河流长度占河流总长度比率halfWidth = _halfRiverWidth,//当前位置和半宽flowDir = _vetexOffset.normalized,//水流流向center = _resultWayPoints[i]//河流路径中心}
);
//保存每条河流的必要数据
m_riverInstance.riverSegmentInfos = this.m_riverSegmentInfos;//保存每条河流的必要数据
m_riverInstance.riverUVWrapAmount = _uvWrap;//河流UVY大小
m_riverInstance.riverLength = _riverLength;//河流总长度
m_riverInstance.segmentAmount = _resultWayPoints.Count - 1;//河流总节点
m_riverInstance.riverDepth = riverDepth;//河流深度

==============================RiverInstance.cs======================================
//RiverInstance类方法
public RiverSegInfo GetFlowSegmentInfo (float UVY) {if (UVY > 0 && riverSegmentInfos.Count > 0) {float _lengthUVYRadio = UVY / riverUVWrapAmount;float _lengthRadioPerSegment = 1f / segmentAmount;foreach (var segInfo in riverSegmentInfos) {if (Mathf.Abs (segInfo.LengthRadio - _lengthUVYRadio) < _lengthRadioPerSegment * 2) {// Debug.Log(segInfo.LengthRadio + " " + _lengthUVYRadio + " " + segInfo.center);return segInfo;}}}return null;}
================================FloatObject.cs=================================
//由hit.textureCoord.y反推水流流向flowDirection
segmentInfo = river.GetFlowSegmentInfo (hit.textureCoord.y);
Vector3 flowDirection = segmentInfo.flowDir;

//这里1.2f - ndotUp是确保当物体处于完全水平的水面时也能向水流方向运动
currentVoxelWaterForce = (1.2f - ndotUp) * flowDirection * water.baseWaterPushForceRadio;
Quaternion surfaceRotation = Quaternion.FromToRotation (this.water.transform.up, (surfaceNormal + flowDirection).normalized);
//沉入水中越少，朝水面法线偏移越厉害，抖动的越厉害
surfaceRotation = Quaternion.Slerp (surfaceRotation, Quaternion.identity, submergedFactor);Vector3 finalVoxelForce = surfaceRotation * ((forceAtSingleVoxel + currentVoxelWaterForce) * submergedFactor);
//添加力
this.rigidbody.AddForceAtPosition (finalVoxelForce, worldPoint);

protected virtual void OnTriggerEnter (Collider other) {//......this.rigidbody.velocity = (currentVoxelWaterForce - rigidbody.velocity) * boundRadio;}}

 //防止物体冲出河道
if(segmentInfox != null){//与河中心的偏移值
Vector3 offset = transform.position - (segmentInfox.center + river.riverDepth * Vector3.down);
///将物体拉回河流中心
this.rigidbody.AddForce(-offset *  centerDragForceRadio,ForceMode.Impulse);}

protected virtual void FixedUpdate () {if (this.water != null && this.voxels.Length > 0) {//将总共的浮力分到每个体元Vector3 forceAtSingleVoxel = this.CalculateMaxBuoyancyForce () / this.voxels.Length;Bounds bounds = this.collider.bounds;//每个体元的高度float voxelHeight = bounds.size.y * this.normalizedVoxelSize;float submergedVolume = 0f;RiverSegInfo segmentInfo = null;for (int i = 0; i < this.voxels.Length; i++) {Vector3 worldPoint = this.transform.TransformPoint (this.voxels[i]);//获取水深度RaycastHit hit = this.GetHitInfoOnWater (worldPoint);float waterLevel = hit.point.y;//体元的深度（体元底部到水面）float deepLevel = waterLevel - worldPoint.y + (voxelHeight / 2f);// 0 - 完全出了水面  1 - 完全沉入水中                 float submergedFactor = Mathf.Clamp (deepLevel / voxelHeight, 0f, 1f);submergedVolume += submergedFactor;//水面的法线Vector3 surfaceNormal = hit.normal;//水对物体的推力计算float ndotUp = Mathf.Clamp01 (Vector3.Dot (surfaceNormal, Vector3.up));segmentInfo = river.GetFlowSegmentInfo (hit.textureCoord.y);if (segmentInfo != null) {Vector3 flowDirection = segmentInfo.flowDir;//这里1.2f - ndotUp是确保当物体处于完全水平的水面时也能向水流方向运动currentVoxelWaterForce = (1.2f - ndotUp) * flowDirection * water.baseWaterPushForceRadio;Quaternion surfaceRotation = Quaternion.FromToRotation (this.water.transform.up, (surfaceNormal + flowDirection).normalized);//沉入水中越少，朝水面法线偏移越厉害，抖动的越厉害surfaceRotation = Quaternion.Slerp (surfaceRotation, Quaternion.identity, submergedFactor);Vector3 finalVoxelForce = surfaceRotation * ((forceAtSingleVoxel + currentVoxelWaterForce) * submergedFactor);//添加力this.rigidbody.AddForceAtPosition (finalVoxelForce, worldPoint);Debug.DrawLine (worldPoint, worldPoint + finalVoxelForce.normalized, Color.blue);Debug.DrawLine (worldPoint, worldPoint + flowDirection);}}submergedVolume /= this.voxels.Length; // 0 - object is fully out of the water, 1 - object is fully submergedthis.rigidbody.drag = Mathf.Lerp (this.initialDrag, this.dragInWater, submergedVolume);this.rigidbody.angularDrag = Mathf.Lerp (this.initialAngularDrag, this.angularDragInWater, submergedVolume);RaycastHit hitx = this.GetHitInfoOnWater (transform.position);RiverSegInfo segmentInfox = river.GetFlowSegmentInfo (hitx.textureCoord.y);//防止物体冲出河道if(segmentInfox != null){Vector3 offset = transform.position - (segmentInfox.center + river.riverDepth * Vector3.down);this.rigidbody.AddForce(-offset *  centerDragForceRadio,ForceMode.Impulse);Debug.DrawLine(transform.position,(segmentInfox.center + river.riverDepth * Vector3.down));}}}