UE4 source code reading_ Bone model and animation system_ Animation node

0. Write it at the front

This article is a collection of personal learning notes , If there is a mistake , I hope you can point out .

1. Animation play ：FAnimNode_SequencePlayer

Related parameters ：

1. UAnimSequenceBase Sequence： Animation clips
2. PlayRateBasis： Playback rate base , By PlayRate except
3. PlayRate： Playback rate , It could be negative , Indicates reverse broadcast
4. PlayRateScaleBiasClamp： Yes PlayRate Extra treatment （ The zoom , Offset and Clamp）, In addition Basis Post operation
5. StartPosition： The starting position of the animation node
6. bLoopAnimation： Cycle animation

1.1 UAnimSequence

Inherited from UAnimSequenceBase, Save the key frame data of the animation sequence , And contains several orbital data
1. The main data ：
TArray RawAnimationData; Raw uncompressed animation keyframe data
TArray SourceRawAnimationData; RawAnimationData Copy of , It is only modified during initialization
Struct FRawAnimSequenceTrack： Single key frame data , Including translation 、 Rotate and scale .
TArray<FVector> PosKeys; TArray<FQuat> RotKeys; TArray<FVector> ScaleKeys;

2. Resource settings
a. Compression Set： Animation compression settings
See animation compression for details

b. Addtive Set： Overlay settings

• TEnumAsByte AdditiveAnimType; The type of superimposed animation
  AAT_None
  AAT_LocalSpaceBase Based on local joint space
  AAT_RotationOffsetMeshSpace Rotation is based on model space , Translation is based on local joint space
• TEnumAsByte RefPoseType; Types of basic postures
  ABPT_None UMETA(DisplayName = “None”),
  ABPT_RefPose UMETA(DisplayName = “Skeleton Reference Pose”),
  ABPT_AnimScaled UMETA(DisplayName = “Selected animation scaled”),
  ABPT_AnimFrame UMETA(DisplayName = “Selected animation frame”),
  

c. RootMotion Set

3. Main function 【TODO】

• GetAnimationPose
• GetBonePose
• AnimCompressionTypes:: DecompressPose
• GetBonePose_Additive

2. RootMotion

2.1 RootMotionMontage

UAnimMontage：
1.ExtractRootMotionFromTrackRange： from Montage Extract within a certain range in the animation track RootMotion data

• ExtractRootMotionFromTrack：
  StartTrackPosition、EndTrackPosition：
  Extract from the specified start time to the end time Montage Internal RootMotion data , Last output to FRootMotionMovementParams object

• GetRootMotionExtractionStepsForTrackRange：
  Due to a Montage The animation track of may consist of multiple animation sequences , So it is extracted in the way of animation sequence by animation RootMotion data , There is TArray in .
  FRootMotionExtractionStep： There is an animation sequence （UAnimSequence） And extraction RootMotion The range of data （ Start position and end position ）
  You may encounter loopback playback （StartTrackPosition>EndTrackPosition）, It needs to be extracted in the correct order .
  If it is loopback , When the animation track has multiple animation sequences, it needs to traverse from the last bit forward .
  Otherwise, it will traverse the animation sequence list in order .
  

• FAnimSegment::GetRootMotionExtractionStepsForTrackRange
  Check whether the start time and end time fall within the range of the animation sequence , If so, add Step list

• ExtractRootMotionFromTrack：

  • After calculating Step After the animation collection , Traverse Step
  • Judge whether the animation is turned on RootMotion.
  • For opening RootMotion Of Step（AnimSequence）
    call AnimSequence->ExtractRootMotionFromRange Extract displacement data
    FTransform StartTransform = ExtractRootTrackTransform(StartTrackPosition, NULL);
    FTransform EndTransform = ExtractRootTrackTransform(EndTrackPosition, NULL);
    =》UAnimSequence::GetBoneTransform
    =》AnimEncodingLegacyBase::GetBoneAtom Finally, call the interface to extract

• Then the extracted displacement data （DeltaTransform） Deposit in FRootMotionMovementParams In the object
  RootMotion.Accumulate(DeltaTransform), This function does not input weights , direct 1 Than 1 The final displacement is fused
  

2.2 RootMotion Anim

FAnimInstanceProxy::TickAssetPlayerInstances：
When RootMotion The model is RootMotionFromEverything when , In this function , According to the weight RootMotion Data extraction to FRootMotionMovementParams In the object

2.3 RootMotion Application and synchronization

See mobile synchronization .

3. Animation overlay ：FAnimNode_ApplyAdditive

1. The main variable ：
FPoseLink Base： Connect base Animation node
FPoseLink Additive： Connect overlay animation nodes
float Alpha： Overlay weights

2. Main interface ：

• FAnimNode_ApplyAdditive::Evaluate_AnyThread
  • obtain Base Two animation poses of node and overlay node
    Base.Evaluate(Output);
    const bool bExpectsAdditivePose = true;
    FPoseContext AdditiveEvalContext(Output, bExpectsAdditivePose);
    Additive.Evaluate(AdditiveEvalContext);
  • Calculate the resulting pose after superposition
    FAnimationRuntime::AccumulateAdditivePose
• FAnimationRuntime::AccumulateAdditivePose
  • According to the type of superposition , Choose different interface calculation
    Local space superposition ：AccumulateLocalSpaceAdditivePoseInternal
    Grid volume space overlay ：AccumulateMeshSpaceRotationAdditiveToLocalPoseInternal
  • In case of curve animation
    BaseCurve.Accumulate(AdditiveCurve, Weight);
• FAnimationRuntime::AccumulateLocalSpaceAdditivePoseInternal
  • Traverse BasePose Every bone of ：
    According to the superposition weight , Calculate the superposition of each bone
    The superposition weight is 1 when ：
    BasePose[BoneIndex].AccumulateWithAdditiveScale(AdditivePose[BoneIndex], VBlendWeight);
    The superposition weight is less than 1 when ：
    FTransform Additive = AdditivePose[BoneIndex];
    FTransform::BlendFromIdentityAndAccumulate(BasePose[BoneIndex], Additive, VBlendWeight);
• AccumulateWithAdditiveScale： Calculate the superimposed Rotation、Translation、Scale data
  Atom： Pose data to be superimposed
  • Deal with rotation ： The superposition of rotations , Multiply by quaternion ：
    const VectorRegister BlendedRotation = VectorMultiply(Atom.Rotation, BlendWeight.Value);
    Rotation = VectorQuaternionMultiply2(BlendedRotation, Rotation);
  • Process translation ： Add vectors
    const VectorRegister BlendedTranslation = VectorMultiply(Atom.Translation, BlendWeight.Value);
    Translation = VectorAdd(Translation, BlendedTranslation);
  • Dealing with scaling ：
    Scale3D = Base_Scale3D * （Default + (Atom_Scale3D * wight)）
• BlendFromIdentityAndAccumulate： It is also calculated after superposition Rotation、Translation、Scale data
  • The translation and zoom processing are consistent with the above
    Although it uses Lerp, but （0,0,0） and Atom Press Weight Do interpolation , It's actually Atom * Weight Result
    
  • Processing of rotation
    

4. Animation blending ：BlendSpace