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前言：
正如上一节所述，IK问题实际上是可以分成“IK Solver”与“IK Goal Solver”两个问题的。
现在，我们手上的“IK Solver”，有：
- Unity Animator 内置的IK系统——Humanoid OnAnimatorIK
- AnimationRigging 的两个IK解算器【SolveTwoBoneIK】、【SolveFABRIK】
- Final IK的IK Solver，比如Biped IK
我们现有的“IK Goal Solver”解决方案，有：
- RayCast + AnimationCurve 的简单实现
- Final IK 的基于速度预测
- 假设我们实现了《刺客信条》的基于路径预测的方案
那么，最终的解决方案，是否可以通过上面的两两排列组合而来呢？答案自然是可以的。
一、 OnAnimatorIK with Velocity Prediction
花活儿就不弄了，我们就简单地依赖于【Unity Animator】的内置IK系统，使用【Final IK】基于速度预测的算法，来实现一版杂交解决方案。
由于算法99%是【Final IK】的，别人又是商业付费插件，以下源码权当学习使用（应该不会侵权吧）。
1. Leg Solver
出于分离【IK Solver】与【IK Goal Solver】的想法，我们定义一个数据交互的接口【IKGoalSolverInterface】便于其他的“IK Solver”快速访问数据。
using UnityEngine;
public interface IKGoalSolverInterface
{
public Vector3 IKOffset { get; } //计算出的IK Goal 位置偏移量
public Vector3 IKPosition { get; } //计算出的IK Goal 最终位置
public Quaternion RotationOffset { get; } //计算出的 IK Goal 旋转偏移
}
当然，现阶段这种写法纯粹是为了统一【Leg Solver】与【Pelvis Solver】的数据访问，存在冗余项。
然后就是定义【Leg Solver】，数据结构与算法基本参考【Final IK】的【RootMotion.FinalIK.Grounding.Leg】
using UnityEngine;
namespace MyHybridIK
{
public class MyLegSolver : IKGoalSolverInterface
{
public Vector3 IKPosition { get; private set; }
public Vector3 IKOffset => Vector3.zero;
public Quaternion RotationOffset { get; private set; }
public Transform footTransform;
public bool isGrounded;
public bool invertFootCenter = false;
public float m_IKOffset { get; private set; }
//Ray Cast Info
public RaycastHit heelHit { get; private set; }
public RaycastHit capsuleHit { get; private set; }
private MyGrounding grounding;
private Vector3 up;
private float lastTime, deltaTime;
private Vector3 lastPosition, transformPosition;
private float heightFromGround;
private Vector3 velocity;
//IK Calculation Paras
private Quaternion toHitNormal, r;
//IK Infos
private bool initiated;
private Vector3 capsuleStart;
private Vector3 capsuleEnd;
/// <summary>
/// 初始化GroundSolver
/// </summary>
/// <param name=&#34;grounding&#34;>Ground参数对象</param>
/// <param name=&#34;transform&#34;>目标足部骨骼的Transform</param>
public void Initiate(MyGrounding grounding, Transform transform)
{
this.grounding = grounding;
this.footTransform = transform;
up = Vector3.up;
IKPosition = transform.position;
RotationOffset = Quaternion.identity;
initiated = true;
lastPosition = transform.position;
lastTime = Time.deltaTime;
}
public void Process()
{
if (!initiated) return;
if (grounding.maxStep <= 0) return;
//Initiate Position;
transformPosition = footTransform.position;
//Time Calculate
deltaTime = Time.time - lastTime;
lastTime = Time.time;
if (deltaTime == 0f) return;
up = grounding.up;
heightFromGround = Mathf.Infinity;
// Calculating velocity
velocity = (transformPosition - lastPosition) / deltaTime;
lastPosition = transformPosition;
var prediction = velocity * grounding.prediction;
//质量区间，暂时不考虑
//if (grounding.footRadius <= 0) grounding.quality = Grounding.Quality.Fastest;
isGrounded = false;
//Best Quality Cast
{
heelHit = GetRaycastHit(invertFootCenter ? -grounding.GetFootCenterOffset() : Vector3.zero);
capsuleHit = GetCapsuleHit(prediction);
if (heelHit.collider != null || capsuleHit.collider != null) isGrounded = true;
SetFootToPlane(capsuleHit.normal, capsuleHit.point, heelHit.point);
}
float offsetTarget = stepHeightFromGround;
if (!grounding.rootGrounded) offsetTarget = 0f;
m_IKOffset = RootMotion.Interp.LerpValue(m_IKOffset, offsetTarget, grounding.footSpeed, grounding.footSpeed);
m_IKOffset = Mathf.Lerp(m_IKOffset, offsetTarget, deltaTime * grounding.footSpeed);
float legHeight = grounding.GetVerticalOffset(transformPosition, grounding.root.position);
float currentMaxOffset = Mathf.Clamp(grounding.maxStep - legHeight, 0f, grounding.maxStep);
m_IKOffset = Mathf.Clamp(m_IKOffset, -currentMaxOffset, m_IKOffset);
RotateFoot();
IKPosition = transformPosition - up * m_IKOffset;
float rW = grounding.footRotationWeight;
RotationOffset = rW >= 1 ? r : Quaternion.Slerp(Quaternion.identity, r, rW);
}
private RaycastHit GetRaycastHit(Vector3 offsetFromHeel)
{
RaycastHit hit = new RaycastHit();
Vector3 origin = transformPosition + offsetFromHeel;
if (grounding.overstepFallsDown)
{
hit.point = origin - up * grounding.maxStep;
}
else
{
hit.point = new Vector3(origin.x, grounding.root.position.y, origin.z);
}
hit.normal = up;
if (grounding.maxStep <= 0f) return hit;
Physics.Raycast(origin + grounding.maxStep * up, -up, out hit, grounding.maxStep * 2, grounding.layerMask, QueryTriggerInteraction.Ignore);
// Since Unity2017 Raycasts will return Vector3.zero when starting from inside a collider
if (hit.point == Vector3.zero && hit.normal == Vector3.zero)
{
if (grounding.overstepFallsDown)
{
hit.point = origin - up * grounding.maxStep;
}
else
{
hit.point = new Vector3(origin.x, grounding.root.position.y, origin.z);
}
}
return hit;
}
private RaycastHit GetCapsuleHit(Vector3 offsetFromHeel)
{
RaycastHit hit = new RaycastHit();
Vector3 f = grounding.GetFootCenterOffset();
if (invertFootCenter) f = -f;
Vector3 origin = transformPosition + f;
if (grounding.overstepFallsDown)
{
hit.point = origin - up * grounding.maxStep;
}
else
{
hit.point = new Vector3(origin.x, grounding.root.position.y, origin.z);
}
hit.normal = up;
// Start point of the capsule
capsuleStart = origin + grounding.maxStep * up;
// End point of the capsule depending on the foot&#39;s velocity.
capsuleEnd = capsuleStart + offsetFromHeel;
if (Physics.CapsuleCast(capsuleStart, capsuleEnd, grounding.footRadius, -up, out hit, grounding.maxStep * 2, grounding.layerMask, QueryTriggerInteraction.Ignore))
{
// Safeguarding from a CapsuleCast bug in Unity that might cause it to return NaN for hit.point when cast against large colliders.
if (float.IsNaN(hit.point.x))
{
hit.point = origin - up * grounding.maxStep * 2f;
hit.normal = up;
}
}
// Since Unity2017 Raycasts will return Vector3.zero when starting from inside a collider
if (hit.point == Vector3.zero && hit.normal == Vector3.zero)
{
if (grounding.overstepFallsDown)
{
hit.point = origin - up * grounding.maxStep;
}
else
{
hit.point = new Vector3(origin.x, grounding.root.position.y, origin.z);
}
}
return hit;
}
private void SetFootToPlane(Vector3 planeNormal, Vector3 planePoint, Vector3 heelHitPoint)
{
planeNormal = RotateNormal(planeNormal);
toHitNormal = Quaternion.FromToRotation(up, planeNormal);
Vector3 pointOnPlane = RootMotion.V3Tools.LineToPlane(transformPosition + up * grounding.maxStep, -up, planeNormal, planePoint);
// Get the height offset of the point on the plane
heightFromGround = GetHeightFromGround(pointOnPlane);
// Making sure the heel doesn&#39;t penetrate the ground
float heelHeight = GetHeightFromGround(heelHitPoint);
heightFromGround = Mathf.Clamp(heightFromGround, -Mathf.Infinity, heelHeight);
}
private Vector3 RotateNormal(Vector3 normal)
{
return normal;
//return Vector3.RotateTowards(up, normal, grounding.maxFootRotationAngle * Mathf.Deg2Rad, deltaTime);
}
private float GetHeightFromGround(Vector3 hitPoint)
{
return grounding.GetVerticalOffset(transformPosition, hitPoint) - rootYOffset;
}
public float stepHeightFromGround
{
get
{
return Mathf.Clamp(heightFromGround, -grounding.maxStep, grounding.maxStep);
}
}
private float rootYOffset
{
get
{
return grounding.GetVerticalOffset(transformPosition, grounding.root.position - up * grounding.heightOffset);
}
}
private void RotateFoot()
{
// Getting the full target rotation
Quaternion rotationOffsetTarget = GetRotationOffsetTarget();
// Slerping the rotation offset
r = Quaternion.Slerp(r, rotationOffsetTarget, deltaTime * grounding.footRotationSpeed);
}
private Quaternion GetRotationOffsetTarget()
{
if (grounding.maxFootRotationAngle <= 0f) return Quaternion.identity;
if (grounding.maxFootRotationAngle >= 180f) return toHitNormal;
return Quaternion.RotateTowards(Quaternion.identity, toHitNormal, grounding.maxFootRotationAngle);
}
}
}
笔者才疏学浅，暂时无法把这段代码的核心算法抽丝剥茧地阐明原理，权当一个“黑匣子”来用吧。
通过【Leg Solver】，我们能基于速度，得到一个脚部的期望平面位置与旋转偏移，他最后的的输出就是IKPosition与 RotationOffset 两个变量。
2. Pelvis Solver
由于Pelvis的计算相对简单，咱就直接Copy-Paste了，代码来自【RootMotion.FinalIK.Grounding.Pelvis】
using UnityEngine;
namespace MyHybridIK
{
public class MyPelvisSolver : IKGoalSolverInterface
{
public Vector3 IKOffset { get; private set; }
public Vector3 IKPosition => Vector3.zero;
public Quaternion RotationOffset => Quaternion.identity;
public float heightOffset { get; private set; }
private MyGrounding grounding;
private Vector3 lastRootPosition;
private float damperF;
private bool initiated;
private float lastTime;
public void Initiate(MyGrounding grounding)
{
this.grounding = grounding;
initiated = true;
OnEnable();
}
public void Reset()
{
this.lastRootPosition = grounding.root.transform.position;
lastTime = Time.deltaTime;
IKOffset = Vector3.zero;
heightOffset = 0f;
}
public void OnEnable()
{
if (!initiated) return;
this.lastRootPosition = grounding.root.transform.position;
lastTime = Time.time;
}
public void Process(float lowestOffset, float highestOffset, bool isGrounded)
{
if (!initiated) return;
float deltaTime = Time.time - lastTime;
lastTime = Time.time;
if (deltaTime <= 0f) return;
float offsetTarget = lowestOffset + highestOffset;
if (!grounding.rootGrounded) offsetTarget = 0f;
// Interpolating the offset
heightOffset = Mathf.Lerp(heightOffset, offsetTarget, deltaTime * grounding.pelvisSpeed);
// Damper
Vector3 rootDelta = (grounding.root.position - lastRootPosition);
lastRootPosition = grounding.root.position;
// Fading out damper when ungrounded
damperF = RootMotion.Interp.LerpValue(damperF, isGrounded ? 1f : 0f, 1f, 10f);
// Calculating the final damper
heightOffset -= grounding.GetVerticalOffset(rootDelta, Vector3.zero) * grounding.pelvisDamper * damperF;
// Update IK value
IKOffset = grounding.up * heightOffset;
}
}
}
他最后的输出是IKOffset ，用于之后对Pelvis进行一定量的偏移。
3. Grounding
大体参考【RootMotion.FinalIK.Grounding】，这个类的作用是指定地面的一系列检测参数，计算Root的一些信息，用于提供给【Leg Solver】与【Pelvis Solver】进行运算。
唯一需要注意的是在使用时，需要手动给面板赋值LeftFootTransform与RightFootTransform，原版是通过【Biped IK】的Reference自动获取的。
using UnityEngine;
namespace MyHybridIK
{
public class MyGrounding : MonoBehaviour
{
[HideInInspector]
public Transform root;
#region Needed Paras
[Header(&#34;Left Foot Transform&#34;)]
public Transform leftFoot;
[Header(&#34;Right Foot Transform&#34;)]
public Transform rightFoot;
public float maxStep = 0.5f;
public LayerMask layerMask;
[HideInInspector]
public Vector3 up = Vector3.up;
public float footSpeed = 2.5f;
[Range(0, 2)]
public float footRadius = 0.15f;
[Range(0, 1)]
public float prediction = 0.05f;
public float footCenterOffset;
public float heightOffset;
public bool rootGrounded => rootHit.distance < maxStep * 2f;
[Range(0, 1)]
public float footRotationWeight = 1;
public float footRotationSpeed = 7f;
public float maxFootRotationAngle = 45f;
public float pelvisSpeed = 5f;
public float pelvisDamper = 0.5f;
public float rootSphereCastRadius = 0.1f;
public bool isGrounded;
public float lowerPelvisWeight = 1f;
public float liftPelvisWeight;
public bool overstepFallsDown = true;
private bool initiated;
private RaycastHit rootHit;
#endregion
public MyLegSolver rightLegSolver;
public MyLegSolver leftLegSolver;
public MyPelvisSolver pelvisSolver;
private MyLegSolver[] legs;
private void Start()
{
root = this.transform;
Initate();
}
private void Initate()
{
rootHit = new RaycastHit();
//构建Leg
leftLegSolver = new MyLegSolver();
leftLegSolver.Initiate(this, leftFoot);
rightLegSolver = new MyLegSolver();
rightLegSolver.Initiate(this, rightFoot);
legs = new MyLegSolver[2];
legs[0] = leftLegSolver;
legs[1] = rightLegSolver;
//构建Pelvis
//....
pelvisSolver = new MyPelvisSolver();
pelvisSolver.Initiate(this);
initiated = true;
}
public void GroundingUpdate()
{
BetterGroundingProcessing();
}
private void BetterGroundingProcessing()
{
if (!initiated) return;
if (layerMask == 0) Debug.LogWarning(&#34;Grounding layers are set to nothing. Please add a ground layer.&#34;);
maxStep = Mathf.Clamp(maxStep, 0f, maxStep);
footRadius = Mathf.Clamp(footRadius, 0.0001f, maxStep);
pelvisDamper = Mathf.Clamp(pelvisDamper, 0f, 1f);
rootSphereCastRadius = Mathf.Clamp(rootSphereCastRadius, 0.0001f, rootSphereCastRadius);
maxFootRotationAngle = Mathf.Clamp(maxFootRotationAngle, 0f, 90f);
prediction = Mathf.Clamp(prediction, 0f, prediction);
footSpeed = Mathf.Clamp(footSpeed, 0f, footSpeed);
//Root Hit
rootHit = GetRootHit();
float lowestOffset = Mathf.NegativeInfinity;
float highestOffset = Mathf.Infinity;
isGrounded = false;
foreach (var leg in legs)
{
leg.Process();
if (leg.m_IKOffset > lowestOffset) lowestOffset = leg.m_IKOffset;
if (leg.m_IKOffset < highestOffset) highestOffset = leg.m_IKOffset;
if (leg.isGrounded) isGrounded = true;
}
// PelvisMove
lowestOffset = Mathf.Max(lowestOffset, 0f);
highestOffset = Mathf.Min(highestOffset, 0f);
pelvisSolver.Process(-lowestOffset * lowerPelvisWeight, -highestOffset * liftPelvisWeight, isGrounded);
}
private RaycastHit GetRootHit(float maxDistanceMlp = 10f)
{
RaycastHit h = new RaycastHit();
Vector3 _up = up;
Vector3 legsCenter = Vector3.zero;
legsCenter += leftLegSolver.footTransform.position;
legsCenter += rightLegSolver.footTransform.position;
legsCenter /= (float)legs.Length;
h.point = legsCenter - _up * maxStep * 10f;
float distMlp = maxDistanceMlp + 1;
h.distance = maxStep * distMlp;
if (maxStep <= 0f) return h;
Physics.SphereCast(legsCenter + _up * maxStep, rootSphereCastRadius, -up, out h, maxStep * distMlp, layerMask, QueryTriggerInteraction.Ignore);
return h;
}
public float GetVerticalOffset(Vector3 p1, Vector3 p2)
{
return p1.y - p2.y;
}
public Vector3 GetFootCenterOffset()
{
return root.forward * footRadius + root.forward * footCenterOffset;
}
}
}
方法逻辑就不一一解释了，咱也是一知半解。
4. RootMotionTool
迁移部分原【Final IK】的计算工具类代码。
namespace RootMotion {
public class Interp
{
public static float LerpValue(float value, float target, float increaseSpeed, float decreaseSpeed)
{
if (value == target) return target;
if (value < target) return Mathf.Clamp(value + Time.deltaTime * increaseSpeed, -Mathf.Infinity, target);
else return Mathf.Clamp(value - Time.deltaTime * decreaseSpeed, target, Mathf.Infinity);
}
}
public static class V3Tools
{
public static Vector3 LineToPlane(Vector3 origin, Vector3 direction, Vector3 planeNormal, Vector3 planePoint)
{
float dot = Vector3.Dot(planePoint - origin, planeNormal);
float normalDot = Vector3.Dot(direction, planeNormal);
if (normalDot == 0.0f) return Vector3.zero;
float dist = dot / normalDot;
return origin + direction.normalized * dist;
}
}
}
5. OnAnimatorIK
“IK Solver”层就很简单了，由于我们依赖的是OnAnimatorIK，直接使用Unity提供的接口进行IK Goal的权重，坐标的赋予就行了。
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using MyHybridIK;
[RequireComponent(typeof(Animator))]
public class BetterInnerIK : MonoBehaviour
{
public bool EnableIK;
public MyGrounding myGrounding;
private Animator m_animator;
[Range(0, 1)] public float pelvisWeight = 1;
[Range(0, 1)] public float leftFootPositionWeight = 1;
[Range(0, 1)] public float rightFootPositionWeight = 1;
[Range(0, 1)] public float leftFootRotationWeight = 1;
[Range(0, 1)] public float rightFootRotationWeight = 1;
public void Start()
{
m_animator = GetComponent<Animator>();
}
private void OnAnimatorIK(int layerIndex)
{
if (!EnableIK)
return;
myGrounding.GroundingUpdate();
PelvisProcess(myGrounding.pelvisSolver);
LeftIKProcess(myGrounding.leftLegSolver);
RightIKProcess(myGrounding.rightLegSolver);
}
private void PelvisProcess(IKGoalSolverInterface pelvisSolver)
{
m_animator.bodyPosition += pelvisSolver.IKOffset * pelvisWeight;
}
private void LeftIKProcess(IKGoalSolverInterface leftFootSolver)
{
m_animator.SetIKPositionWeight(AvatarIKGoal.LeftFoot, leftFootPositionWeight);
m_animator.SetIKRotationWeight(AvatarIKGoal.LeftFoot, leftFootRotationWeight);
var originalRotation = m_animator.GetIKRotation(AvatarIKGoal.LeftFoot);
var finalRotation = Quaternion.Slerp(Quaternion.identity, leftFootSolver.RotationOffset, leftFootRotationWeight) * originalRotation;
m_animator.SetIKRotation(AvatarIKGoal.LeftFoot, finalRotation);
m_animator.SetIKPosition(AvatarIKGoal.LeftFoot, leftFootSolver.IKPosition);
}
private void RightIKProcess(IKGoalSolverInterface rightFootSolver)
{
m_animator.SetIKPositionWeight(AvatarIKGoal.RightFoot, rightFootPositionWeight);
m_animator.SetIKRotationWeight(AvatarIKGoal.RightFoot, rightFootRotationWeight);
var originalRotation = m_animator.GetIKRotation(AvatarIKGoal.RightFoot);
var finalRotation = Quaternion.Slerp(Quaternion.identity, rightFootSolver.RotationOffset, leftFootRotationWeight) * originalRotation;
m_animator.SetIKRotation(AvatarIKGoal.RightFoot, finalRotation);
m_animator.SetIKPosition(AvatarIKGoal.RightFoot, rightFootSolver.IKPosition);
}
}
至此，【IK Goal Solver】的问题使用【Final IK】进行解决，【IK Solver】的问题交由【Humanoid Animator IK】解决，我们基本上实现了一版解决方案。
二、表现测试
走一遍Unity内置IK的设置流程：把模型动画设置成Humanoid、打开Animator Layer的IK Pass、挂载脚本等，最后，我们的角色实体大约长这样：
平平无奇小脚本
跑起来试试？
Cool，表现跟Final IK 相差无几
三、性能优化
1. Timeline统计
瞅一瞅Profiler的Timeline：
IK Goal Solver的用时几乎占了整个动画用时的一半
IK Sovler应该就是这个Job，用时反而很低
就如上一节我们所得出的结论，IK Goal Solver的耗时才是最大的那一环，真是恐怖如斯。
那么【Final IK】表现如何呢？配置一个使用【Final IK】的实体，看看表现：
总体0.084ms
SolverManager的处理是包含了ReadTransform，IK Solve，WriteTransform等等流程，一个实体总计0.08ms左右的用时，感觉跟用Unity的内置IK半斤八两。
把实体数弄到10个试试。
OnAnimatorIK的表现：
10个OnAnimatorIK串行执行
算上后面计算，的大约0.35ms消耗
Final IK的表现：
10个SolverManager串行执行
大约0.52ms消耗
这就有意思了，两种方法的耗时差值达到了0.2ms，为什么会出现这种情况？
实际上，由于我们的“IK Goal Solver”的算法基本一致，这一块的耗时两者其实是差不多的。
而“IK Solver”的算法，大家都是用三角函数解析，耗时也是相差无几。
真正出现差距的地方在那儿？还记得OnAnimatorIK的后面的逻辑块吗？
顾名思义，IK Solver Job
写入Transform的Job
非常朴素的猜想就是，OnAnimatorIK只是提供“IK Goal Solver”的接口，决定好了IK Goal的旋转位置后，交由【Animators.IKAndTwistBoneJob】与【Animators.WriteJob】执行多线程统一计算、写入。而事实也正是如此：
看见那个“over 12 threads”了吗
多线程Job也显示了他就是采用了这种策略
而【Final IK】呢，那就是完全的串行计算了，算一个写一个，产生了0.2ms的差距。
2. 并行化
基于上述分析，很明显的一点，如果我们能把OnAnimator的计算使用多线程并行计算（比如JobSystem），可想而知的用时会大幅减少。
换句话说，本来就应该把复数实体的“IK Goal Solver”问题给并行化计算，因为他们的计算完全独立，相互之间不存在任何依赖。
上面那种10个Solver的串行表现看着就很傻啊。
3. 优化Physics检测
当然，这是复数个实体的情况，那么单个实体的性能怎么提升呢？
虽然从现在的表现来看，一个实体的cost顶天0.1ms的消耗，但是我们就是不满意，就是想降低，有没有什么办法呢？
在【Final IK】插件的【Grounder Biped】上，有一个“Quality”选项：
Quality = Best
把他改成“Fast”，看看对比。
使用“Fast”
使用“Best”
提升很明显，而在代码中，Fast使用“RayCast”代替了“SphereCast”，舍弃了最耗时的“CapsuleCast”，牺牲了部分准确度换来了性能提升。
4. 颗粒度细分
这一节纯属笔者臆想。
现阶段实现的FootIK，在所有的动画状态都使用一套算法。有没有一种可能，在idle静止状态时，可以不用Prediction，就简单地检测地面；在Walk/Running时，再使用Prediction算法；而在某些待机动画中，则完全禁止IK（比如《原神》的角色在进行待机动画时，是完全禁止了IK的）。
又比如玩家角色和AI角色使用不同的IK算法，又或者进行视距剔除之类的balabala。
嗯，只能说深究下去，优化方向还是蛮多的hhh。
四、小结
终于把IK的本质问题给弄懂了，也着手实现了各种IK方案（虽然核心算法是抄Final IK）的，只是没有完全弄懂Final IK的预测算法有点遗憾。
如果可以，我真希望IK的研究就此告一段落，呜呜呜。 |
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发表于 2022-7-25 16:26
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