How to get BoneWeights and BoneIndices of skeletalMesh c++?

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1

Hello,
I want to know the boneWeights and boneIndices for each vertex of a skeletalMesh
Thanks.

2

I found the answer myself.

Here is how:

  • First you need to get the target mesh.
  • Then get the vertices.
  • After that we need to loop them, and use the index of the iteration to get the boneIndices and boneWeights of each vertex.
  • Now we have a uint8 value, we need to access the data inside this byte buffer.
  • We will cast this vertex.InfluenceBones[0] to Int, where index 0 for the first bone index and 1 for the second and so on for 3 and 4.
  • Now for boneWeights, almost the same for the previous step.
  • Firstly, we will cast vertex.InfluencesWeights[0] to Int then cast it to double and divide it with 255.0
    where index 0 for the first bone index and 1 for the second and so on for 3 and 4.

“255.0” is the maximum number of each byte in that buffer

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3

I used this method, but I got error bone index. The same FBX, many vertices bone index is 0(rootBone), but in Unity, no any vertices bone index is 0(rootBone)

4

How did you do it? The GetSkeletalMeshResource method doesn’t even exist in the Unreal Engine

5

In 4.27 and 5.0+ I use this:

FSkeletalMeshLODRenderData& LODData = Mesh->SkeletalMesh->GetResourceForRendering()->LODRenderData[0];
	FSkinWeightVertexBuffer* SkinWeightBuffer = &lodd.SkinWeightVertexBuffer;
 	TArray <FSkinWeightInfo> SkinWeightInfo;
 	SkinWeightBuffer->GetSkinWeights(SkinWeightInfo);

Note that you will still need to map the bone indices from SkinWeightInfo to their corresponding bone index inside the SkeletalMesh’s BoneMap such as:

int32 BoneIndex = SkinWeightBuffer.GetBoneIndex(vertexindex, 0);
int32 ActualBone = LODData.RenderSections[0].BoneMap[BoneIndex];
FName BoneName = SKMesh->GetBoneName(ActualBone);

Each entry in the SkinWeightInfo array corresponds to a mesh vertex

1 Like
6

Are you sure on the variable definitions and bond index limits?

What used to work originally is probably been increased by at least one order of magnitude since they released metahumans.

Not that limiting the index to a smaller value is incorrect. Matrer of fact it can never go out of index.

The original solution is also wrong.
You can’t cast to int and then cast to double without loosing precision.
In the realm of animation you need that precision.

Seems to me that the /255 part claiming its the maximum byte means that the wrong math is being used for it entierly.
Then again, it does depend on what value is in fact store by the index.

The point is, if you divide 1.5 by 255 it isn’t the same as dividing 1 by 255.
And that’s basically what the code above would do.