constructor (textureNames, backgroundIsEnvMap)
    {
        this.textureNames = textureNames;
        this.backgroundIsEnvMap = backgroundIsEnvMap;
    }
@param {string[]} textureNames Urls of the environment map images in this order:
posx, negx, posy, negy, posz, negz.
@param {boolean} backgroundIsEnvMap Use the environment map as background.