stride3d/stride · error · InvalidOperationException

Skeleton nodes are not sorted

Error message

Skeleton nodes are not sorted

What it means

StaticMeshColliderShape.BuildAndShareMeshes walks a mesh's skeleton node hierarchy top-down and caches each node's world transform. Nodes must be ordered so a child appears after its parent; when node.ParentIndex points at a node at or after the current index, the parent's transform is not yet computed, so the code throws this InvalidOperationException to fail fast on malformed skeleton data.

Solutions

1. Re-sort the mesh's skeleton nodes so every parent appears before all of its children before calling BuildAndShareMeshes
2. Re-export the asset with the original modeling tool / a fixed exporter that emits a topologically ordered node hierarchy
3. Validate the loaded model's node ordering (each node.ParentIndex < its index, or ParentIndex == -1 for roots) and reject/reorder the data early
4. Check for cycles or self-referencing ParentIndex values in the source asset file

Example fix

// before (unsorted data fed straight to the collider)
var shape = new StaticMeshColliderShape(meshData);

// after (guard: reorder nodes so parents precede children)
var sorted = meshData.Nodes.OrderBy(n => n.ParentIndex == -1 ? -1 : 1).ToList();
// or topologically sort by ParentIndex before building:
if (meshData.Nodes.Any((n, i) => n.ParentIndex >= i))
    throw new ArgumentException("Skeleton nodes must be sorted parent-first");

static bool IsSkeletonSorted(IReadOnlyList<MeshSkeletonNode> nodes)
{
    for (int i = 0; i < nodes.Count; i++)
    {
        int p = nodes[i].ParentIndex;
        if (p != -1 && p >= i) return false;
    }
    return true;
}

bool HasValidSkeleton(MeshSkeleton skeleton) =>
    skeleton?.Nodes == null ? false :
    skeleton.Nodes.All(n => n.ParentIndex == -1 || n.ParentIndex < skeleton.Nodes.IndexOf(n));

try { shape.BuildAndShareMeshes(); }
catch (InvalidOperationException ex) when (ex.Message == "Skeleton nodes are not sorted")
{
    meshData.Nodes = TopologicallySortByParent(meshData.Nodes);
    shape.BuildAndShareMeshes();
}

When it happens

Trigger: Calling BuildAndShareMeshes on a mesh whose skeleton node array is not topologically sorted — i.e. a node whose ParentIndex is >= its own index (self-parent, forward reference, or cyclic parent chain).

Common situations: Importing models from exporters that emit nodes in arbitrary order instead of parent-first order; hand-written or procedurally generated mesh/skeleton data; asset files corrupted or modified by custom tooling that reordered nodes.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• Mesh seems to have no volume; triangle rasterization…
• is already assigned to , it cannot be shared with
• Collider type is missing in , please fill an issue or fix it
• Failed to find index buffer while building a convex hull.
• Failed to find index buffer while building a convex hull.

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/ab52a434b43b24c1. Report an issue: GitHub.

Appendix: source

Thrown at sources/engine/Stride.Physics/Shapes/StaticMeshColliderShape.cs:134

                }
            }
            
            Matrix[] nodeTransforms = null;
            if (model.Skeleton != null)
            {
                var nodesLength = model.Skeleton.Nodes.Length;
                nodeTransforms = new Matrix[nodesLength];
                nodeTransforms[0] = Matrix.Identity;
                for (var i = 0; i < nodesLength; i++)
                {
                    var node = model.Skeleton.Nodes[i];
                    Matrix.Transformation(ref node.Transform.Scale, ref node.Transform.Rotation, ref node.Transform.Position, out var localMatrix);

                    Matrix worldMatrix;
                    if (node.ParentIndex != -1)
                    {
                        if (node.ParentIndex >= i)
                            throw new InvalidOperationException("Skeleton nodes are not sorted");
                        var nodeTransform = nodeTransforms[node.ParentIndex];
                        Matrix.Multiply(ref localMatrix, ref nodeTransform, out worldMatrix);
                    }
                    else
                    {
                        worldMatrix = localMatrix;
                    }

                    if (i != 0)
                    {
                        nodeTransforms[i] = worldMatrix;
                    }
                }
            }

            int totalVerts = 0, totalIndices = 0;
            foreach (var meshData in model.Meshes)
            {

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