Crash when switching to LOD with LOD bone removal settings.

[okqi]

FAnimNode_KawaiiPhysics::InitModifyBones

//CalcBoneLength(ModifyBones[0], BoneContainer.GetRefPoseCompactArray());
CalcBoneLength(ModifyBones[0], BoneContainer.GetRefPoseArray());

[pafuhana1213]

Hi,
I tried it but this issue did not occur.
Would you please share with me how to repro it?

thanks

[sergi-gonzalez]

Hi @pafuhana1213 ,

First of all, our team loves Kawaii Physics, thanks a lot for sharing your work.

I am testing the plugin on UE5 and I got the same crash in the same place:
CalcBoneLength(ModifyBones[0], Bones);
\Plugins\KawaiiPhysics\Source\KawaiiPhysics\Private\AnimNode_KawaiiPhysics.cpp LN 200

I have investigated the problem and the crash happens because Bone.BoneRef.BoneIndex is greater than the number of transforms in RefBonePose.
In our case LOD0 has 140 bones and LOD2 has 78 bones. The crash happened when InitModifyBones is called when BoneContainer.CalculatedForLOD is 2 and one modify bone had the boneIndex 90 (RefBonePose contains 78 entries).

The following fix seems to work as expected (changes tagged with [hexworks]):

void FAnimNode_KawaiiPhysics::CalcBoneLength(FKawaiiPhysicsModifyBone& Bone, const TArray<FTransform>& RefBonePose, const FBoneContainer& BoneContainer)//[hexworks] - Added BoneContainer
{
	if (Bone.ParentIndex < 0)
	{
		Bone.LengthFromRoot = 0.0f;
	}
	else
	{
		if (!Bone.bDummy)
		{
			FCompactPoseBoneIndex CompactPoseBoneIndex = Bone.BoneRef.GetCompactPoseIndex(BoneContainer);//[hexworks] - Fix crash indexing Bone.BoneRef.BoneIndex
			Bone.LengthFromRoot = ModifyBones[Bone.ParentIndex].LengthFromRoot
				+ RefBonePose[CompactPoseBoneIndex.GetInt()].GetLocation().Size();//[hexworks] - Fix crash indexing Bone.BoneRef.BoneIndex
		}
		else
		{
			Bone.LengthFromRoot = ModifyBones[Bone.ParentIndex].LengthFromRoot + DummyBoneLength;
		}
		
		TotalBoneLength = FMath::Max(TotalBoneLength, Bone.LengthFromRoot);
	}

	for (int ChildIndex : Bone.ChildIndexs)
	{
		CalcBoneLength(ModifyBones[ChildIndex], RefBonePose, BoneContainer);//[hexworks] - Added BoneContainer
	}
}

It's also required to fix the lines that call CalcBoneLength adding BoneContainer as last parameter.
Could you please check the fix and integrate it in the repo?

Best regards,

sergi

[taka1arg]

お疲れ様です。

私の方でも配列のオーバーランが発生し
CalcBoneLength(ModifyBones[0], BoneContainer.GetRefPoseArray());
に変更して対応しました。

レベル起動後にスケルタルメッシュをカメラの遠く（LODが適用される距離）にスポーンすると発生ように思われます。

[pafuhana1213]

Hi guys,
Sorry for my late reply...
I succeeded to repro this issue on UE5.1 and committed a9bf985 to fix this now.

thanks!