UnrealEngineUWP/Engine/Source/Runtime/AnimGraphRuntime/Private/BoneControllers/AnimNode_Trail.cpp

// Copyright 1998-2015 Epic Games, Inc. All Rights Reserved.

#include "AnimGraphRuntimePrivatePCH.h"
#include "BoneControllers/AnimNode_Trail.h"

/////////////////////////////////////////////////////
// FAnimNode_Trail

FAnimNode_Trail::FAnimNode_Trail()
	: ChainLength(2)
	, ChainBoneAxis(EAxis::X)
	, bInvertChainBoneAxis(false)
	, bLimitStretch(false)
	, TrailRelaxation(10)
	, StretchLimit(0)
	, FakeVelocity(FVector::ZeroVector)
	, bActorSpaceFakeVel(false)
	, bHadValidStrength(false)
{
}

void FAnimNode_Trail::Update(const FAnimationUpdateContext& Context)
{
	FAnimNode_SkeletalControlBase::Update(Context);

	ThisTimstep = Context.GetDeltaTime();
}

void FAnimNode_Trail::GatherDebugData(FNodeDebugData& DebugData)
{
	FString DebugLine = DebugData.GetNodeName(this);

	DebugLine += "(";
	AddDebugNodeData(DebugLine);
	DebugLine += FString::Printf(TEXT(" Active: %s)"), *TrailBone.BoneName.ToString());
	DebugData.AddDebugItem(DebugLine);

	ComponentPose.GatherDebugData(DebugData);
}

void FAnimNode_Trail::EvaluateBoneTransforms(USkeletalMeshComponent* SkelComp, FCSPose<FCompactPose>& MeshBases, TArray<FBoneTransform>& OutBoneTransforms)
{
	check(OutBoneTransforms.Num() == 0);

	if( ChainLength < 2 )
	{
		return;
	}

	// The incoming BoneIndex is the 'end' of the spline chain. We need to find the 'start' by walking SplineLength bones up hierarchy.
	// Fail if we walk past the root bone.

	const FBoneContainer& BoneContainer = MeshBases.GetPose().GetBoneContainer();
	FCompactPoseBoneIndex WalkBoneIndex = TrailBone.GetCompactPoseIndex(BoneContainer);

	TArray<FCompactPoseBoneIndex> ChainBoneIndices;
	ChainBoneIndices.AddZeroed(ChainLength);

	ChainBoneIndices[ChainLength - 1] = WalkBoneIndex;

	for (int32 i = 1; i < ChainLength; i++)
	{
		// returns to avoid a crash
		// @TODO : shows an error message why failed
		if (WalkBoneIndex == 0)
		{
			return;
		}

		// Get parent bone.
		WalkBoneIndex = BoneContainer.GetParentBoneIndex(WalkBoneIndex);

		//Insert indices at the start of array, so that parents are before children in the array.
		int32 TransformIndex = ChainLength - (i + 1);
		ChainBoneIndices[TransformIndex] = WalkBoneIndex;
	}

	OutBoneTransforms.AddZeroed(ChainLength);

	// If we have >0 this frame, but didn't last time, record positions of all the bones.
	// Also do this if number has changed or array is zero.
	bool bHasValidStrength = (Alpha > 0.f);
	if(TrailBoneLocations.Num() != ChainLength || (bHasValidStrength && !bHadValidStrength))
	{
		TrailBoneLocations.Empty();
		TrailBoneLocations.AddZeroed(ChainLength);

		for(int32 i=0; i<ChainBoneIndices.Num(); i++)
		{
			FCompactPoseBoneIndex ChildIndex = ChainBoneIndices[i];
			const FTransform& ChainTransform = MeshBases.GetComponentSpaceTransform(ChildIndex);
			TrailBoneLocations[i] = ChainTransform.GetTranslation();
		}
		OldLocalToWorld = SkelComp->GetTransformMatrix();
	}
	bHadValidStrength = bHasValidStrength;

	// transform between last frame and now.
	FMatrix OldToNewTM = OldLocalToWorld * SkelComp->GetTransformMatrix().InverseFast();

	// Add fake velocity if present to all but root bone
	if(!FakeVelocity.IsZero())
	{
		FVector FakeMovement = -FakeVelocity * ThisTimstep;

		if (bActorSpaceFakeVel && SkelComp->GetOwner())
		{
			const FTransform BoneToWorld(SkelComp->GetOwner()->GetActorQuat(), SkelComp->GetOwner()->GetActorLocation());
			FakeMovement = BoneToWorld.TransformVector(FakeMovement);
		}

		FakeMovement = SkelComp->GetTransformMatrix().InverseTransformVector(FakeMovement);
		// Then add to each bone
		for(int32 i=1; i<TrailBoneLocations.Num(); i++)
		{
			TrailBoneLocations[i] += FakeMovement;
		}
	}

	// Root bone of trail is not modified.
	FCompactPoseBoneIndex RootIndex = ChainBoneIndices[0]; 
	const FTransform& ChainTransform = MeshBases.GetComponentSpaceTransform(RootIndex);
	OutBoneTransforms[0] = FBoneTransform(RootIndex, ChainTransform);
	TrailBoneLocations[0] = ChainTransform.GetTranslation();

	// Starting one below head of chain, move bones.
	for(int32 i=1; i<ChainBoneIndices.Num(); i++)
	{
		// Parent bone position in component space.
		FCompactPoseBoneIndex ParentIndex = ChainBoneIndices[i - 1];
		FVector ParentPos = TrailBoneLocations[i-1];
		FVector ParentAnimPos = MeshBases.GetComponentSpaceTransform(ParentIndex).GetTranslation();

		// Child bone position in component space.
		FCompactPoseBoneIndex ChildIndex = ChainBoneIndices[i];
		FVector ChildPos = OldToNewTM.TransformPosition(TrailBoneLocations[i]); // move from 'last frames component' frame to 'this frames component' frame
		FVector ChildAnimPos = MeshBases.GetComponentSpaceTransform(ChildIndex).GetTranslation();

		// Desired parent->child offset.
		FVector TargetDelta = (ChildAnimPos - ParentAnimPos);

		// Desired child position.
		FVector ChildTarget = ParentPos + TargetDelta;

		// Find vector from child to target
		FVector Error = ChildTarget - ChildPos;

		// Calculate how much to push the child towards its target
		float Correction = FMath::Clamp<float>(ThisTimstep * TrailRelaxation, 0.f, 1.f);

		// Scale correction vector and apply to get new world-space child position.
		TrailBoneLocations[i] = ChildPos + (Error * Correction);

		// If desired, prevent bones stretching too far.
		if(bLimitStretch)
		{
			float RefPoseLength = TargetDelta.Size();
			FVector CurrentDelta = TrailBoneLocations[i] - TrailBoneLocations[i-1];
			float CurrentLength = CurrentDelta.Size();

			// If we are too far - cut it back (just project towards parent particle).
			if( (CurrentLength - RefPoseLength > StretchLimit) && CurrentLength > SMALL_NUMBER )
			{
				FVector CurrentDir = CurrentDelta / CurrentLength;
				TrailBoneLocations[i] = TrailBoneLocations[i-1] + (CurrentDir * (RefPoseLength + StretchLimit));
			}
		}

		// Modify child matrix
		OutBoneTransforms[i] = FBoneTransform(ChildIndex, MeshBases.GetComponentSpaceTransform(ChildIndex));
		OutBoneTransforms[i].Transform.SetTranslation(TrailBoneLocations[i]);

		// Modify rotation of parent matrix to point at this one.

		// Calculate the direction that parent bone is currently pointing.
		FVector CurrentBoneDir = OutBoneTransforms[i-1].Transform.TransformVector( GetAlignVector(ChainBoneAxis, bInvertChainBoneAxis) );
		CurrentBoneDir = CurrentBoneDir.GetSafeNormal(SMALL_NUMBER);

		// Calculate vector from parent to child.
		FVector NewBoneDir = FVector(OutBoneTransforms[i].Transform.GetTranslation() - OutBoneTransforms[i - 1].Transform.GetTranslation()).GetSafeNormal(SMALL_NUMBER);

		// Calculate a quaternion that gets us from our current rotation to the desired one.
		FQuat DeltaLookQuat = FQuat::FindBetween(CurrentBoneDir, NewBoneDir);
		FTransform DeltaTM( DeltaLookQuat, FVector(0.f) );

		// Apply to the current parent bone transform.
		FTransform TmpMatrix = FTransform::Identity;
		TmpMatrix.CopyRotationPart(OutBoneTransforms[i - 1].Transform);
		TmpMatrix = TmpMatrix * DeltaTM;
		OutBoneTransforms[i - 1].Transform.CopyRotationPart(TmpMatrix);
	}

	// For the last bone in the chain, use the rotation from the bone above it.
	OutBoneTransforms[ChainLength - 1].Transform.CopyRotationPart(OutBoneTransforms[ChainLength - 2].Transform);

	// Update OldLocalToWorld
	OldLocalToWorld = SkelComp->GetTransformMatrix();
}

bool FAnimNode_Trail::IsValidToEvaluate(const USkeleton* Skeleton, const FBoneContainer& RequiredBones) 
{
	// if bones are valid
	return (TrailBone.IsValid(RequiredBones));
}

void FAnimNode_Trail::InitializeBoneReferences(const FBoneContainer& RequiredBones) 
{
	TrailBone.Initialize(RequiredBones);
}

FVector FAnimNode_Trail::GetAlignVector(EAxis::Type AxisOption, bool bInvert)
{
	FVector AxisDir;

	if (AxisOption == EAxis::X)
	{
		AxisDir = FVector(1, 0, 0);
	}
	else if (AxisOption == EAxis::Y)
	{
		AxisDir = FVector(0, 1, 0);
	}
	else
	{
		AxisDir = FVector(0, 0, 1);
	}

	if (bInvert)
	{
		AxisDir *= -1.f;
	}

	return AxisDir;
}