code: function isMultiPassGeometry( primitives ) {
  
    if ( primitives.length < 2 ) return false;
  
    const primitive0 = primitives[ 0 ];
    const targets0 = primitive0.targets || [];
  
    if ( primitive0.indices === undefined ) return false;
  
    for ( let i = 1, il = primitives.length; i < il; i++ ) {
  
      const primitive = primitives[ i ];
  
      if ( primitive0.mode !== primitive.mode ) return false;
      if ( primitive.indices === undefined ) return false;
      if ( primitive.extensions && primitive.extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ] ) return false;
      if ( !isObjectEqual( primitive0.attributes, primitive.attributes ) ) return false;
  
      const targets = primitive.targets || [];
  
      if ( targets0.length !== targets.length ) return false;
  
      for ( let j = 0, jl = targets0.length; j < jl; j++ ) {
  
        if ( !isObjectEqual( targets0[ j ], targets[ j ] ) ) return false;
  
      }
  
    }
  
    return true;
  
  }
docs: Checks if we can build a single Mesh with MultiMaterial from multiple primitives.
  Returns true if all primitives use the same attributes/morphAttributes/mode
  and also have index. Otherwise returns false.
  
  @param {Array<GLTF.Primitive>} primitives
  @return {Boolean}