Unity-Technologies/UnityCsReference · error · ArgumentException

instance has not materials

Error message

instance {instanceIndex} has not materials

What it means

GetMaterialIndex throws ArgumentException 'instance {n} has not materials' when the resolved Instance has submeshMaterialIndices.Length == 0. The instance passed the range guard but has no submesh->material mapping, so no submesh (including index 0) is valid. This indicates the instance contributed no materials to the bake (e.g. it was skipped or has no renderer materials).

Solutions

1. Check theInstance.submeshMaterialIndices.Length > 0 before calling GetMaterialIndex.
2. Treat a material-less instance as 'no material' and skip/report it.
3. Investigate upstream if an instance you expect to have materials is empty.

Example fix

// before
int mIdx = lightBaker.GetMaterialIndex(instIdx, subIdx);

// after
Instance inst = lightBaker.instance(instIdx);
if (inst.submeshMaterialIndices.Length == 0) continue;
int mIdx = lightBaker.GetMaterialIndex(instIdx, subIdx);

Instance inst = lightBaker.instance(instanceIndex);
if (inst.submeshMaterialIndices.Length > 0)
    int mIdx = lightBaker.GetMaterialIndex(instanceIndex, submeshIndex);

When it happens

Trigger: Calling GetMaterialIndex on an instance whose submeshMaterialIndices array is empty; iterating submeshes 0..k without first confirming the instance has any.

Common situations: Instances that were baked but stripped of materials; LOD/parent objects with no material assignment; assuming every instance has at least one material.

Related errors

• instanceIndex must be between 0 and
• index must be between 0 and
• index must be between 0 and
• material for submesh
• submeshIndex must be between 0 and

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/67f28d9531632454. Report an issue: GitHub.

Appendix: source

Thrown at Editor/Mono/GI/LightBaker.bindings.cs:516

        {
            if (index >= materialCount)
                throw new ArgumentException($"index must be between 0 and {materialCount - 1}, but was {index}");
            Material material = Internal_GetMaterial(index);
            return material;
        }
        public void SetMaterial(uint index, Material material)
        {
            if (index >= materialCount)
                throw new ArgumentException($"index must be between 0 and {materialCount - 1}, but was {index}");
            Internal_SetMaterial(index, material);
        }
        public int GetMaterialIndex(uint instanceIndex, uint submeshIndex)
        {
            if (instanceIndex >= instanceCount)
                throw new ArgumentException($"instanceIndex must be between 0 and {instanceCount - 1}, but was {instanceIndex}");
            Instance theInstance = instance(instanceIndex);
            if (theInstance.submeshMaterialIndices.Length == 0)
                throw new ArgumentException($"instance {instanceIndex} has not materials");
            if (submeshIndex >= theInstance.submeshMaterialIndices.Length)
                throw new ArgumentException($"submeshIndex must be between 0 and {theInstance.submeshMaterialIndices.Length - 1}, but was {submeshIndex}");
            return theInstance.submeshMaterialIndices[submeshIndex];
        }
        extern uint Internal_GetLightCount();
        public uint GetLightCount()
        {
            return Internal_GetLightCount();
        }
        extern Light Internal_GetLight(uint index);
        extern void Internal_SetLight(uint index, Light light);
        public Light GetLight(uint index)
        {
            if (index >= GetLightCount())
                throw new ArgumentException($"index must be between 0 and {GetLightCount() - 1}, but was {index}");
            return Internal_GetLight(index);
        }
        public void SetLight(uint index, Light light)

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