why FSkinWeightVertexBuffer.GetBoneIndex() != USkeletalMeshComponent->GetBoneIndex()

General Feedback & Requests
, ,
1

During runtime I want to know the worldposition of some vertices of my model.

My approach after several trial and errors is to querry the BoneIndex from the SkeletalMeshComponent by FName

int32 boneIndex = Skel->GetBoneIndex(boneName1);

and then I would get Indices influenced by that bone, using the FSkinWeightVertexBuffer

const FSkeletalMeshLODRenderData& LOD = Skel->GetSkeletalMeshRenderData()->LODRenderData[LODIndex];
const FSkinWeightVertexBuffer& Buffer = LOD.SkinWeightVertexBuffer;

TArray<uint32> vertices;
for (uint32 it = 0; it < Buffer.GetNumVertices(); ++it) {
    for (uint32 bonInfluence = 0; bonInfluence < Buffer.GetMaxBoneInfluences(); ++bonInfluence) {
        int32 bonIndex = static_cast<int32>(Buffer.GetBoneIndex(it, bonInfluence));
	uint8 boneWeight = Buffer.GetBoneWeight(it, bonInfluence);
        if (bonIndex == boneIndex) {
		vertices.Add(it);
        }
   }
}

and get the Locations of those vertices with

Skel->GetSkinnedVertexPosition(Skel, vertices[i], LOD, Buffer)

I visualize those vertices later and it shows that vertices are the wrong ones!

If I get for instance the boneIndex 458 from Skel->GetBoneIndex(boneName1), the actual index I would need is 444 to get the right vertices

My actual question is, why do they differ, and how do I get reliably the correct boneIndex, or rather the vertices that are influenced by a certain bone?

2

I have the same issue. :confused:

3

@starot found the trick here: How to get TRUE bone index by vertex in 5.1.1 <3

Have to works with Lod RenderSections and BoneMap

    // Iterate over all sections
    for (const FSkelMeshRenderSection& SkelMeshSection : LODData.RenderSections)
    {
        const TArray<FBoneIndexType>& BoneMap = SkelMeshSection.BoneMap;

        // Retrieve vertex indices for this section
        TArray<uint32> SectionVertexIndices;
        LODData.MultiSizeIndexContainer.GetIndexBuffer(SectionVertexIndices);

        for (uint32 i = SkelMeshSection.BaseIndex; i < static_cast<uint32>(SkelMeshSection.BaseIndex + SkelMeshSection.NumTriangles * 3); i++)
        {
            int32 VertexIndex = SectionVertexIndices[i];

            for (int32 InfluenceIdx = 0; InfluenceIdx < MaxInfluences; InfluenceIdx++)
            {
                int32 LocalBoneIndex = SkinWeightVertexBuffer.GetBoneIndex(VertexIndex, InfluenceIdx);
                if (LocalBoneIndex >= BoneMap.Num()) continue; // Ensure we are within bounds

                int32 GlobalBoneIndex = BoneMap[LocalBoneIndex];
                float BoneWeight = SkinWeightVertexBuffer.GetBoneWeight(VertexIndex, InfluenceIdx) / 65535.0f;

                FName CurrentBoneName = SkeletalMeshComponent->GetBoneName(GlobalBoneIndex);

                if (GlobalBoneIndex == BoneIndexInRefSkeleton && BoneWeight > 0)
                {
                    FVector VertexWorldPosition = Locations[VertexIndex];

                    FLinearColor A = FLinearColor::Blue;
                    FLinearColor B = FLinearColor::Red;
                    FLinearColor VertexColor = A + BoneWeight * (B - A);
                    DrawDebugPoint(SkeletalMeshComponent->GetWorld(), VertexWorldPosition, Size, VertexColor.ToFColor(false), false, Duration);
                }
            }
        }
    }