function ModelShape(id, shape, indicesLength, shapeUV, posFunction, vtxFunction) {
            this._indicesLength = 0; // length of the shape in the model indices array
            this.shapeID = id;
            this._shape = shape;
            this._indicesLength = indicesLength;
            this._shapeUV = shapeUV;
            this._positionFunction = posFunction;
            this._vertexFunction = vtxFunction;
        }
Creates a ModelShape object. This is an internal simplified reference to a mesh used as for a model to replicate particles from by the SPS.
SPS internal tool, don't use it manually.