Since I am engaged into something needs bone position of a ref pose in UE4, and UE4 does not provide access to it, so we need to calculate it manually.
We can calculate bone position like this:
void get_ref_pose_bone_comp_space_transform(TArray<FTransform>& outResult, USkeletalMeshComponent* inSkelComp)
We can use
USkeletalMeshComponent::GetPreviousComponentTransformsArray() to get current bone position in component space.