Extracting the normals from a Model at runtime

December 2, 2010

In case this is useful to somebody: the following code will extract the normals from a ModelMeshPart at runtime. Usually this is best done with a custom ModelProcessor, but that's not always possible.

private static Vector3[] GetNormals(ModelMeshPart meshPart)
    if (meshPart.VertexBuffer == null)
        return null;

    VertexBuffer vb = meshPart.VertexBuffer;
    if (meshPart.VertexBuffer.Tag != null) // Vertex buffers can be, and usually are, shared between ModelMeshPart's.
        return (Vector3[]) meshPart.VertexBuffer.Tag;

    VertexDeclaration vd = vb.VertexDeclaration;
    VertexElement[] elements = vd.GetVertexElements();

    Func<VertexElement,bool> normalElementPredicate = ve => ve.VertexElementUsage == VertexElementUsage.Normal && ve.VertexElementFormat == VertexElementFormat.Vector3;
    if (!elements.Any(normalElementPredicate))
        return null;

    VertexElement normalElement = elements.First(normalElementPredicate);

    Vector3[] normals = new Vector3[vb.VertexCount];
    vb.GetData(normalElement.Offset, normals, 0, vb.VertexCount, vd.VertexStride);

    return normals;

In fact, I'm not going to use this code, because I think I've found a way to use a custom ModelProcessor for my scenario, but perhaps it will be of use to somebody else.

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