【Unity学习笔记】第十七 Quaternion 中 LookRotation、Lerp、Slerp、RotateTowards等方法辨析与验证

转载请注明出处: https://blog.csdn.net/weixin_44013533/article/details/138909256

作者：CSDN@|Ringleader|

- Quaternion API 速览
- FromToRotation在Transform中的应用
- LookRotation 中upwards取Vector3.up和 transform.up的区别
- 旋转时如何保持Y轴不变，但朝向目标旋转呢？
- 不同旋转方法案例
- lerp与LerpUnclamped区别
- Quaternion.Slerp 、Quaternion.RotateTowards区别
- Lerp、Slerp比较
- Quaternion * operator
- 总结

主要参考：

Unity手册 & Quaternion API
Unity3D - 详解Quaternion类（二）
【Unity编程】Unity中关于四元数的API详解

Quaternion API 速览

创建旋转：

FromToRotation 创建一个从 fromDirection 旋转到 toDirection 的旋转。
LookRotation 使用指定的 forward 和 upwards 方向创建旋转。
AngleAxis 创建一个围绕 axis 旋转 angle 度的旋转。
Angle 返回两个旋转 a 和 b 之间的角度（以度为单位）。(180°以内)

操作旋转：

Lerp 在 a 和 b 之间插入 t，然后对结果进行标准化处理。参数 t 被限制在 [0, 1] 范围内。
Slerp 在四元数 a 与 b 之间按比率 t 进行球形插值。参数 t 限制在范围 [0, 1] 内。
RotateTowards 将旋转 from 向 to 旋转。

Transform 类还提供了一些方法可用于处理 Quaternion 旋转：Transform.Rotate & Transform.RotateAround

FromToRotation在Transform中的应用

Transform中有很多Quaternion的应用，比如获取对象的xyz轴向量在世界坐标系下的表示，就用到了FromToRotation：

   ///<para>The red axis of the transform in world space.</para>public Vector3 right{get => this.rotation * Vector3.right;set => this.rotation = Quaternion.FromToRotation(Vector3.right, value);}///<para>The green axis of the transform in world space.</para>public Vector3 up{get => this.rotation * Vector3.up;set => this.rotation = Quaternion.FromToRotation(Vector3.up, value);}///<para>Returns a normalized vector representing the blue axis of the transform in world space.public Vector3 forward{get => this.rotation * Vector3.forward;set => this.rotation = Quaternion.LookRotation(value);}

LookRotation 中upwards取Vector3.up和 transform.up的区别

public static Quaternion LookRotation (Vector3 forward, Vector3 upwards= Vector3.up);

因为LookRotation 会使对象Z轴与forward参数向量对齐，X 轴与Vector3.Cross(upwards,forward)这个叉乘结果对齐，Y 轴与 Z 和 X 的叉乘（Vector3.Cross(transform.forward,transform.right) ）对齐。（注意unity左手坐标系，叉乘方向）

所以会看到当upwards取世界空间的向上和模型空间的向上是有区别的。

或者说，upwards取模型空间的向上时对象可以绕自身z轴旋转，对象状态并不固定。
在这里插入图片描述

public class LookRotationTest : MonoBehaviour
{public Transform obt_forward;public Transform obt_worldUp;public Transform obt_selfUp;public bool showCrossResult = false;// 验证叉乘方向用private void Update(){// upwards取世界空间的向上LookForward(obt_worldUp, obt_forward.position - obt_worldUp.position, Vector3.up);// upwards取模型空间的向上LookForward(obt_selfUp,obt_forward.position - obt_selfUp.position, obt_selfUp.up);}private void LookForward(Transform obt, Vector3 forward,Vector3 upwards){obt.rotation = Quaternion.LookRotation(forward, upwards);var position = obt.position;Debug.DrawLine(obt_forward.position, position);Debug.DrawLine(position, position + obt.right * 5, Color.red);Debug.DrawLine(position, position + obt.up * 5, Color.green);Debug.DrawLine(position, position + obt.forward * 5, Color.blue);// 验证叉乘方向, 叉乘结果与LookFoward结果一致if (showCrossResult){var X_cross = Vector3.Cross(upwards,forward);var Y_cross = Vector3.Cross(obt.forward,obt.right);Debug.DrawLine(position, position + X_cross * 10, Color.cyan);Debug.DrawLine(position, position + Y_cross * 10, Color.yellow);}}
}

旋转时如何保持Y轴不变，但朝向目标旋转呢？

使用Vector3.ProjectOnPlane将目标方向投影到xz平面。
在这里插入图片描述

Lookat, FromToRotation and LookRotation?

不同旋转方法案例

下面代码比较了transform.forward 、Transform.LookAt、Quaternion.FromToRotation、LookRotation、Quaternion.RotateTowards、Vector3.ProjectOnPlane等不同方法

public class CompareImmediateAndStep : MonoBehaviour
{public Transform turret;public Transform enemy;private string str;private void Update(){var targetTowards = enemy.position - turret.position;// 立刻跟随敌人if (Input.GetKey(KeyCode.Alpha1)){turret.forward = targetTowards;str = "使用turret.forward = targetTowards;";}// 上面本质也是使用FromToRotation方法if (Input.GetKey(KeyCode.Alpha2)){turret.rotation = Quaternion.FromToRotation(Vector3.forward, targetTowards);str = "使用turret.rotation = Quaternion.FromToRotation(Vector3.forward, targetTowards);";}if (Input.GetKey(KeyCode.Alpha3)){//当FromToRotation的fromDirection参数是forward轴时，可以用LookRotationturret.rotation = Quaternion.LookRotation(targetTowards);str = "turret.rotation = Quaternion.LookRotation(targetTowards);";}if (Input.GetKey(KeyCode.Alpha4)){turret.LookAt(enemy.transform);str = "turret.LookAt(enemy.transform);";}// 插值方式，加入旋转速度if (Input.GetKey(KeyCode.Alpha5)){var fromToRotation = Quaternion.LookRotation(targetTowards);turret.rotation = Quaternion.RotateTowards(turret.rotation, fromToRotation, 45 * Time.deltaTime);str = "使用worldUp的Quaternion.RotateTowards";}// 保持对象Y轴朝向不变，将targetTowards进行投影if (Input.GetKey(KeyCode.Alpha6)){var fromToRotation = Quaternion.LookRotation(Vector3.ProjectOnPlane(targetTowards,Vector3.up),Vector3.up);turret.rotation = Quaternion.RotateTowards(turret.rotation, fromToRotation, 45 * Time.deltaTime);str = "保持Y轴朝向不变，将targetTowards进行投影";}DrawAxis(turret);DrawAxis(enemy);}private void DrawAxis(Transform obt){DrawAxis(obt, Color.red, Color.green, Color.blue, 5);}private void DrawAxis(Transform obt, Color xc, Color yc, Color zc, float length){if (obt.gameObject.activeInHierarchy){var position = obt.position;Debug.DrawLine(position, position + obt.right * length, xc);Debug.DrawLine(position, position + obt.up * length, yc);Debug.DrawLine(position, position + obt.forward * length, zc);}}private Rect rect = new Rect(100, 100, 600, 50);private void OnGUI(){DrawLabel(rect, str);}private static void DrawLabel(Rect rect1, String str){var style = new GUIStyle{fontSize = 38,wordWrap = true};GUI.Label(rect1, str, style);}
}

lerp与LerpUnclamped区别

区别就是Unclam不会钳值，而且取负数时会从to→from旋转。
在这里插入图片描述

Vector3: Lerp vs LerpUnclamped

Quaternion.Slerp 、Quaternion.RotateTowards区别

RotateTowards本质也是使用了SlerpUnclamped方法，但其旋转速度恒定，不会因target变化而改变。

public static Quaternion RotateTowards(Quaternion from, Quaternion to, float maxDegreesDelta){float num = Quaternion.Angle(from, to);return (double) num == 0.0 ? to : Quaternion.SlerpUnclamped(from, to, Mathf.Min(1f, maxDegreesDelta / num));}

这篇帖子 Use Quaternion.RotateTowards() instead of Quaternion.Slerp() 提到了：

如果旋转操作的from和to都已知，使用 Quaternion.Slerp() - 例如打开一扇门或箱子盖。
如果要以恒定角速度转向某物，则使用 Quaternion.RotateTowards() - 例如，在塔防类游戏中要转向塔的炮塔。

Lerp、Slerp比较

Quaternion的插值分析及总结
Lerp求得的是四元数在圆上的弦上的等分，而Slerp求得的是四元数载圆上的圆弧的等分

进行代码验证：

public class SlerpTest : MonoBehaviour
{public Transform obtLerp;public Transform obtSlerp;public Transform towardsObt;public bool towardsNotChanged;private Quaternion currentLookRotation,lastLookRotation;private Quaternion initRotationLerp, initRotationSlerp;public float speed = 0.1f;float total = 0.0f;private void Start(){lastLookRotation = Quaternion.LookRotation(towardsObt.position-obtLerp.position);initRotationLerp = obtLerp.rotation;initRotationSlerp = obtSlerp.rotation;}void Update(){CompareSlerpAndLerp();}private void CompareSlerpAndLerp(){currentLookRotation = Quaternion.LookRotation(towardsObt.position - obtLerp.position);towardsNotChanged = currentLookRotation == lastLookRotation;// 改变朝向时，重置初始位置、重置totalif (!towardsNotChanged){lastLookRotation = currentLookRotation;// 重置执行Lerp、Slerp时的初始旋转initRotationLerp = obtLerp.rotation;initRotationSlerp = obtSlerp.rotation;total = 0;return;}lastLookRotation = currentLookRotation;total += Time.deltaTime * speed;if (total >= 1.0f)total = 1.0f;obtLerp.rotation = Quaternion.Lerp(initRotationLerp, currentLookRotation, total);obtSlerp.rotation = Quaternion.Slerp(initRotationSlerp, currentLookRotation, total);DrawAxis(obtLerp);DrawAxis(obtSlerp, Color.cyan, Color.magenta, Color.yellow, 10);}private void DrawAxis(Transform obt){DrawAxis(obt, Color.red, Color.green, Color.blue, 5);}private void DrawAxis(Transform obt,Color xc,Color yc,Color zc,float length){if (obt.gameObject.activeInHierarchy){var position = obt.position;Debug.DrawLine(position, position + obt.right * length, xc);Debug.DrawLine(position, position + obt.up * length, yc);Debug.DrawLine(position, position + obt.forward * length, zc);}}private Rect rect = new Rect(100, 100, 600, 50);private void OnGUI(){DrawLabel(rect,"Total:"+total);}private void DrawLabel(Rect rect1, String str){var style = new GUIStyle{fontSize = 38,wordWrap = true};GUI.Label(rect1, str, style);}
}