Unity-Technologies/UnityCsReference · error · ArgumentException

index must be between 0 and {materialCount - 1}, but was {in

Error message

index must be between 0 and {materialCount - 1}, but was {index}

What it means

LightBaker.GetMaterial(uint index) throws ArgumentException when index >= materialCount. The material list holds materials referenced by baked instances/submeshes; count reflects how many distinct materials were baked.

Source

Thrown at Editor/Mono/GI/LightBaker.bindings.cs:500

        {
            if (index >= terrainCount)
                throw new ArgumentException($"index must be between 0 and {terrainCount - 1}, but was {index}");
            Terrain terrain = Internal_GetTerrain(index);
            return terrain;
        }

        public extern Vector2[] GetUV1VertexData(uint meshIndex);

        public extern uint meshCount { get; }
        public extern uint heightmapCount { get; }
        public extern uint holemapCount { get; }
        public extern uint materialCount { get; }
        extern Material Internal_GetMaterial(uint index);
        extern void Internal_SetMaterial(uint index, Material material);
        public Material GetMaterial(uint index)
        {
            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}");

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Read materialCount and iterate [0, count).
2. Use GetMaterialIndex(instanceIndex, submeshIndex) to map a submesh to a global material index before calling GetMaterial.
3. Re-query materialCount after material/scene changes.

Example fix

// before
var mat = lightBaker.GetMaterial(globalIndex);

// after
if (globalIndex < lightBaker.materialCount)
    var mat = lightBaker.GetMaterial(globalIndex);

uint n = lightBaker.materialCount;
if (index < n)
    var mat = lightBaker.GetMaterial(index);

When it happens

Trigger: Calling GetMaterial with an index not bounded by materialCount; using a submesh/material index from one instance as a global material index.

Common situations: Confusing per-instance submesh indices with global material indices; stale materialCount after a re-bake that changed materials.

Related errors

• instanceIndex must be between 0 and {instanceCount - 1}, but
• submeshIndex must be between 0 and {theInstance.submeshMater
• index must be between 0 and {albedoTextureCount - 1}, but wa
• index must be between 0 and {emissiveTextureCount - 1}, but
• index must be between 0 and {instanceCount - 1}, but was {in

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/6b55c7725c213c64. Report an issue: GitHub.