function getProgramKey$1(lightNumbers) {
    var defineStr = [];
    var lightTypes = Object.keys(lightNumbers);
    lightTypes.sort();
    for (var i = 0; i < lightTypes.length; i++) {
        var lightType = lightTypes[i];
        defineStr.push(lightType + ' ' + lightNumbers[lightType]);
    }
    var key = defineStr.join('\n');

    if (programKeyCache$1[key]) {
        return programKeyCache$1[key];
    }

    var id = util$1.genGUID();
    programKeyCache$1[key] = id;
    return id;
}
@function
@name clone
@return {clay.Camera}
@memberOf clay.Camera.prototype