基本原理
每个动画(AnimSequence)要指定一个重定向源(RetargetSource)，然后实时的时候根据重定向源的TPose和当前角色的TPose进行重定向的计算。
实时重定向的计算方法又分为五种: Animation, Skeleton, AnimationScale, AnimationRelative, OrientAndScale
骨骼重定向方法的设置粒度是骨骼级别，具体使用方法参见官方文档
官方文档:
https://docs.unrealengine.com/en-US/Engine/Animation/AnimationRetargeting/index.html
我印象中的常用操作，通常有问题都是用以下操作解决:
某个动画重定向结果不对：在动画编辑器里指定下重定向源
某根骨骼的效果结果不对：在骨骼树窗口里更改此骨骼的重定向设置
新角色的动画，需要在最大化骨架编辑器里新增一下新角色的重定向源
双手武器重定向后，挂接效果不对。这时候可能就需要ik了，ik和重定向是一个搭档。
实时重定向源码
UE中获取任何的骨骼动画数据，都会调用 UAnimSequence::GetBonePose
GetBonePose就像古代的关隘，连接动画逻辑（动画树、Montage等）与动画数据
压缩动画的重定向
压缩动画的重定向核心代码就直接在GetBonePose函数的末尾
由于压缩动画重定向和非压缩动画的重定向的原理是一样的，只是读取动画数据的方式不同，所以重定向源码分析放到下节
非压缩动画的重定向
GetBonePose函数并没有直接处理非压缩动画的重定向，而是通过如下调用栈:
BuildPoseFromRawData -> RetargetBoneTransform -> FAnimationRuntime::RetargetBoneTransform
所以非压缩动画的重定向核心逻辑如下
void FAnimationRuntime::RetargetBoneTransform(const USkeleton* MySkeleton, const FName& RetargetSource, FTransform& BoneTransform, const int32 SkeletonBoneIndex, const FCompactPoseBoneIndex& BoneIndex, const FBoneContainer& RequiredBones, const bool bIsBakedAdditive)
{
if (MySkeleton)
{
switch (MySkeleton->GetBoneTranslationRetargetingMode(SkeletonBoneIndex))
{
case EBoneTranslationRetargetingMode::AnimationScaled:
{
// @todo - precache that in FBoneContainer when we have SkeletonIndex->TrackIndex mapping. So we can just apply scale right away.
const TArray<FTransform>& SkeletonRefPoseArray = MySkeleton->GetRefLocalPoses(RetargetSource);
const float SourceTranslationLength = SkeletonRefPoseArray[SkeletonBoneIndex].GetTranslation().Size();
if (SourceTranslationLength > KINDA_SMALL_NUMBER)
{
const float TargetTranslationLength = RequiredBones.GetRefPoseTransform(BoneIndex).GetTranslation().Size();
BoneTransform.ScaleTranslation(TargetTranslationLength / SourceTranslationLength);
}
break;
}
case EBoneTranslationRetargetingMode::Skeleton:
{
BoneTransform.SetTranslation(bIsBakedAdditive ? FVector::ZeroVector : RequiredBones.GetRefPoseTransform(BoneIndex).GetTranslation());
break;
}
case EBoneTranslationRetargetingMode::AnimationRelative:
{
// With baked additive animations, Animation Relative delta gets canceled out, so we can skip it.
// (A1 + Rel) - (A2 + Rel) = A1 - A2.
if (!bIsBakedAdditive)
{
const TArray<FTransform>& AuthoredOnRefSkeleton = MySkeleton->GetRefLocalPoses(RetargetSource);
const TArray<FTransform>& PlayingOnRefSkeleton = RequiredBones.GetRefPoseCompactArray();
const FTransform& RefPoseTransform = RequiredBones.GetRefPoseTransform(BoneIndex);
// Apply the retargeting as if it were an additive difference between the current skeleton and the retarget skeleton.
BoneTransform.SetRotation(BoneTransform.GetRotation() * AuthoredOnRefSkeleton[SkeletonBoneIndex].GetRotation().Inverse() * RefPoseTransform.GetRotation());
BoneTransform.SetTranslation(BoneTransform.GetTranslation() + (RefPoseTransform.GetTranslation() - AuthoredOnRefSkeleton[SkeletonBoneIndex].GetTranslation()));
BoneTransform.SetScale3D(BoneTransform.GetScale3D() * (RefPoseTransform.GetScale3D() * AuthoredOnRefSkeleton[SkeletonBoneIndex].GetSafeScaleReciprocal(AuthoredOnRefSkeleton[SkeletonBoneIndex].GetScale3D())));
BoneTransform.NormalizeRotation();
}
break;
}
case EBoneTranslationRetargetingMode::OrientAndScale:
{
if (!bIsBakedAdditive)
{
const FRetargetSourceCachedData& RetargetSourceCachedData = RequiredBones.GetRetargetSourceCachedData(RetargetSource);
const TArray<FOrientAndScaleRetargetingCachedData>& OrientAndScaleDataArray = RetargetSourceCachedData.OrientAndScaleData;
const TArray<int32>& CompactPoseIndexToOrientAndScaleIndex = RetargetSourceCachedData.CompactPoseIndexToOrientAndScaleIndex;
// If we have any cached retargeting data.
if ((OrientAndScaleDataArray.Num() > 0) && (CompactPoseIndexToOrientAndScaleIndex.Num() == RequiredBones.GetCompactPoseNumBones()))
{
const int32 OrientAndScaleIndex = CompactPoseIndexToOrientAndScaleIndex[BoneIndex.GetInt()];
if (OrientAndScaleIndex != INDEX_NONE)
{
const FOrientAndScaleRetargetingCachedData& OrientAndScaleData = OrientAndScaleDataArray[OrientAndScaleIndex];
const FVector AnimatedTranslation = BoneTransform.GetTranslation();
// If Translation is not animated, we can just copy the TargetTranslation. No retargeting needs to be done.
const FVector NewTranslation = (AnimatedTranslation - OrientAndScaleData.SourceTranslation).IsNearlyZero(BONE_TRANS_RT_ORIENT_AND_SCALE_PRECISION) ?
OrientAndScaleData.TargetTranslation :
OrientAndScaleData.TranslationDeltaOrient.RotateVector(AnimatedTranslation) * OrientAndScaleData.TranslationScale;
BoneTransform.SetTranslation(NewTranslation);
}
}
}
break;
}
}
}
}
这个函数只是一根骨骼的重定向计算。
当前角色的TPose就存在RequiredBones里。
重定向源的TPose都是存在最大化骨架MySkeleton中的，根据AnimSequence.RetargetSource来获取当前的重定向源数据
大部分的实时重定向的方法主要改的就是骨骼的translation，scale和rotation不会动，AnimationRelative模式例外
- Animation: 纯动画，不做任何重定向
- Skeleton: 直接用角色TPose的translation
- AnimationScale: 用动画的Translation，但是会根据当前角色的TPose和RetargetSource的TPose的比例对Translation进行缩放。 和AnimationRelative相比，delta是用除法算出来的，且只改Translation
- AnimationRelative: 用动画的Translation，scale，rotation，但是会根据当前角色的TPose和RetargetSource的TPose的差值对动画的prs进行增减。和AnimationScale相比，delta是用减法算出来的。
- OrientAndScale: 用动画的Translation，实时会根据OrientAndScaleData的信息对Translation进行变换
OrientAndScale模式下的OrientAndScaleData的计算
- OrientAndScaleData.TranslationDeltaOrient是一个四元数旋转: 是从重定向源的骨骼translation(SourceSkelTransDir)到当前角色TPose的骨骼Translation(TargetSkelTransDir)的一个旋转
- OrientAndScaleData.TranslationScale是一个scale的除法: 当前角色TPose的骨骼Translation的长度(TargetSkelTransLength) / 重定向源的骨骼translation的长度(SourceSkelTransLength)
const FRetargetSourceCachedData& FBoneContainer::GetRetargetSourceCachedData(const FName& InRetargetSourceName) const
{
FRetargetSourceCachedData* RetargetSourceCachedData = RetargetSourceCachedDataLUT.Find(InRetargetSourceName);
if (!RetargetSourceCachedData)
{
RetargetSourceCachedData = &RetargetSourceCachedDataLUT.Add(InRetargetSourceName);
// Build Cached Data for OrientAndScale retargeting.
const TArray<FTransform>& AuthoredOnRefSkeleton = AssetSkeleton->GetRefLocalPoses(InRetargetSourceName);
const TArray<FTransform>& PlayingOnRefSkeleton = GetRefPoseCompactArray();
const int32 CompactPoseNumBones = GetCompactPoseNumBones();
RetargetSourceCachedData->CompactPoseIndexToOrientAndScaleIndex.Reset();
for (int32 CompactBoneIndex = 0; CompactBoneIndex < CompactPoseNumBones; CompactBoneIndex++)
{
const int32& SkeletonBoneIndex = CompactPoseToSkeletonIndex[CompactBoneIndex];
if (AssetSkeleton->GetBoneTranslationRetargetingMode(SkeletonBoneIndex) == EBoneTranslationRetargetingMode::OrientAndScale)
{
const FVector SourceSkelTrans = AuthoredOnRefSkeleton[SkeletonBoneIndex].GetTranslation();
const FVector TargetSkelTrans = PlayingOnRefSkeleton[CompactBoneIndex].GetTranslation();
// If translations are identical, we don't need to do any retargeting
if (!SourceSkelTrans.Equals(TargetSkelTrans, BONE_TRANS_RT_ORIENT_AND_SCALE_PRECISION))
{
const float SourceSkelTransLength = SourceSkelTrans.Size();
const float TargetSkelTransLength = TargetSkelTrans.Size();
// this only works on non zero vectors.
if (!FMath::IsNearlyZero(SourceSkelTransLength * TargetSkelTransLength))
{
const FVector SourceSkelTransDir = SourceSkelTrans / SourceSkelTransLength;
const FVector TargetSkelTransDir = TargetSkelTrans / TargetSkelTransLength;
const FQuat DeltaRotation = FQuat::FindBetweenNormals(SourceSkelTransDir, TargetSkelTransDir);
const float Scale = TargetSkelTransLength / SourceSkelTransLength;
const int32 OrientAndScaleIndex = RetargetSourceCachedData->OrientAndScaleData.Add(FOrientAndScaleRetargetingCachedData(DeltaRotation, Scale, SourceSkelTrans, TargetSkelTrans));
// initialize CompactPoseBoneIndex to OrientAndScale Index LUT on demand
if (RetargetSourceCachedData->CompactPoseIndexToOrientAndScaleIndex.Num() == 0)
{
RetargetSourceCachedData->CompactPoseIndexToOrientAndScaleIndex.Init(INDEX_NONE, CompactPoseNumBones);
}
RetargetSourceCachedData->CompactPoseIndexToOrientAndScaleIndex[CompactBoneIndex] = OrientAndScaleIndex;
}
}
}
}
}
return *RetargetSourceCachedData;
}
