pipeline.js

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var js = require('../platform/js');
var LoadingItems = require('./loading-items');
var ItemState = LoadingItems.ItemState;

function flow (pipe, item) {
    var pipeId = pipe.id;
    var itemState = item.states[pipeId];
    var next = pipe.next;
    var pipeline = pipe.pipeline;

    if (item.error || itemState === ItemState.WORKING || itemState === ItemState.ERROR) {
        return;
    }
    else if (itemState === ItemState.COMPLETE) {
        if (next) {
            flow(next, item);
        }
        else {
            pipeline.flowOut(item);
        }
    }
    else {
        item.states[pipeId] = ItemState.WORKING;
        // Pass async callback in case it's a async call
        var result = pipe.handle(item, function (err, result) {
            if (err) {
                item.error = err;
                item.states[pipeId] = ItemState.ERROR;
                pipeline.flowOut(item);
            }
            else {
                // Result can be null, then it means no result for this pipe
                if (result) {
                    item.content = result;
                }
                item.states[pipeId] = ItemState.COMPLETE;
                if (next) {
                    flow(next, item);
                }
                else {
                    pipeline.flowOut(item);
                }
            }
        });
        // If result exists (not undefined, null is ok), then we go with sync call flow
        if (result instanceof Error) {
            item.error = result;
            item.states[pipeId] = ItemState.ERROR;
            pipeline.flowOut(item);
        }
        else if (result !== undefined) {
            // Result can be null, then it means no result for this pipe
            if (result !== null) {
                item.content = result;
            }
            item.states[pipeId] = ItemState.COMPLETE;
            if (next) {
                flow(next, item);
            }
            else {
                pipeline.flowOut(item);
            }
        }
    }
}

/**
 * !#en
 * A pipeline describes a sequence of manipulations, each manipulation is called a pipe.<br/>
 * It's designed for loading process. so items should be urls, and the url will be the identity of each item during the process.<br/>
 * A list of items can flow in the pipeline and it will output the results of all pipes.<br/>
 * They flow in the pipeline like water in tubes, they go through pipe by pipe separately.<br/>
 * Finally all items will flow out the pipeline and the process is finished.
 *
 * !#zh
 * pipeline 描述了一系列的操作，每个操作都被称为 pipe。<br/>
 * 它被设计来做加载过程的流程管理。所以 item 应该是 url，并且该 url 将是在处理中的每个 item 的身份标识。<br/>
 * 一个 item 列表可以在 pipeline 中流动，它将输出加载项经过所有 pipe 之后的结果。<br/>
 * 它们穿过 pipeline 就像水在管子里流动，将会按顺序流过每个 pipe。<br/>
 * 最后当所有加载项都流出 pipeline 时，整个加载流程就结束了。
 * @class Pipeline
 */
/**
 * !#en
 * Constructor, pass an array of pipes to construct a new Pipeline,
 * the pipes will be chained in the given order.<br/>
 * A pipe is an object which must contain an `id` in string and a `handle` function,
 * the id must be unique in the pipeline.<br/>
 * It can also include `async` property to identify whether it's an asynchronous process.
 * !#zh
 * 构造函数，通过一系列的 pipe 来构造一个新的 pipeline，pipes 将会在给定的顺序中被锁定。<br/>
 * 一个 pipe 就是一个对象，它包含了字符串类型的 ‘id’ 和 ‘handle’ 函数，在 pipeline 中 id 必须是唯一的。<br/>
 * 它还可以包括 ‘async’ 属性以确定它是否是一个异步过程。
 *
 * @method constructor
 * @param {Array} pipes
 * @example
 *  var pipeline = new Pipeline([
 *      {
 *          id: 'Downloader',
 *          handle: function (item, callback) {},
 *          async: true
 *      },
 *      {id: 'Parser', handle: function (item) {}, async: false}
 *  ]);
 */
var Pipeline = function (pipes) {
    this._pipes = pipes;
    this._cache = js.createMap(true);

    for (var i = 0; i < pipes.length; ++i) {
        var pipe = pipes[i];
        // Must have handle and id, handle for flow, id for state flag
        if (!pipe.handle || !pipe.id) {
            continue;
        }

        pipe.pipeline = this;
        pipe.next = i < pipes.length - 1 ? pipes[i+1] : null;
    }
};

Pipeline.ItemState = ItemState;

var proto = Pipeline.prototype;

/**
 * !#en
 * Insert a new pipe at the given index of the pipeline. <br/>
 * A pipe must contain an `id` in string and a `handle` function, the id must be unique in the pipeline.
 * !#zh
 * 在给定的索引位置插入一个新的 pipe。<br/>
 * 一个 pipe 必须包含一个字符串类型的 ‘id’ 和 ‘handle’ 函数，该 id 在 pipeline 必须是唯一标识。
 * @method insertPipe
 * @param {Object} pipe The pipe to be inserted
 * @param {Number} index The index to insert
 */
proto.insertPipe = function (pipe, index) {
    // Must have handle and id, handle for flow, id for state flag
    if (!pipe.handle || !pipe.id || index > this._pipes.length) {
        cc.warnID(4921);
        return;
    }

    if (this._pipes.indexOf(pipe) > 0) {
        cc.warnID(4922);
        return;
    }

    pipe.pipeline = this;

    var nextPipe = null;
    if (index < this._pipes.length) {
        nextPipe = this._pipes[index];
    }

    var previousPipe = null;
    if (index > 0) {
        previousPipe = this._pipes[index-1];
    }

    if (previousPipe) {
        previousPipe.next = pipe;
    }
    pipe.next = nextPipe;

    this._pipes.splice(index, 0, pipe);
};

/**
 * !en
 * Insert a pipe to the end of an existing pipe. The existing pipe must be a valid pipe in the pipeline.
 * !zh
 * 在当前 pipeline 的一个已知 pipe 后面插入一个新的 pipe。
 * @method insertPipeAfter
 * @param {Object} refPipe An existing pipe in the pipeline.
 * @param {Object} newPipe The pipe to be inserted.
 */
proto.insertPipeAfter = function (refPipe, newPipe)  {
    var index = this._pipes.indexOf(refPipe);
    if (index < 0) {
        return;
    }
    this.insertPipe(newPipe, index+1);
};

/**
 * !#en
 * Add a new pipe at the end of the pipeline. <br/>
 * A pipe must contain an `id` in string and a `handle` function, the id must be unique in the pipeline.
 * !#zh
 * 添加一个新的 pipe 到 pipeline 尾部。 <br/>
 * 该 pipe 必须包含一个字符串类型 ‘id’ 和 ‘handle’ 函数，该 id 在 pipeline 必须是唯一标识。
 * @method appendPipe
 * @param {Object} pipe The pipe to be appended
 */
proto.appendPipe = function (pipe) {
    // Must have handle and id, handle for flow, id for state flag
    if (!pipe.handle || !pipe.id) {
        return;
    }

    pipe.pipeline = this;
    pipe.next = null;
    if (this._pipes.length > 0) {
        this._pipes[this._pipes.length - 1].next = pipe;
    }
    this._pipes.push(pipe);
};

/**
 * !#en
 * Let new items flow into the pipeline. <br/>
 * Each item can be a simple url string or an object,
 * if it's an object, it must contain `id` property. <br/>
 * You can specify its type by `type` property, by default, the type is the extension name in url. <br/>
 * By adding a `skips` property including pipe ids, you can skip these pipe. <br/>
 * The object can contain any supplementary property as you want. <br/>
 * !#zh
 * 让新的 item 流入 pipeline 中。<br/>
 * 这里的每个 item 可以是一个简单字符串类型的 url 或者是一个对象,
 * 如果它是一个对象的话，他必须要包含 ‘id’ 属性。<br/>
 * 你也可以指定它的 ‘type’ 属性类型，默认情况下，该类型是 ‘url’ 的后缀名。<br/>
 * 也通过添加一个 包含 ‘skips’ 属性的 item 对象，你就可以跳过 skips 中包含的 pipe。<br/>
 * 该对象可以包含任何附加属性。
 * @method flowIn
 * @param {Array} items
 * @example
 *  pipeline.flowIn([
 *      'res/Background.png',
 *      {
 *          id: 'res/scene.json',
 *          type: 'scene',
 *          name: 'scene',
 *          skips: ['Downloader']
 *      }
 *  ]);
 */
proto.flowIn = function (items) {
    var i, pipe = this._pipes[0], item;
    if (pipe) {
        // Cache all items first, in case synchronous loading flow same item repeatly
        for (i = 0; i < items.length; i++) {
            item = items[i];
            this._cache[item.id] = item;
        }
        for (i = 0; i < items.length; i++) {
            item = items[i];
            flow(pipe, item);
        }
    }
    else {
        for (i = 0; i < items.length; i++) {
            this.flowOut(items[i]);
        }
    }
};

/*
 * !#en
 * Let new items flow into the pipeline and give a callback when the list of items are all completed. <br/>
 * This is for loading dependencies for an existing item in flow, usually used in a pipe logic. <br/>
 * For example, we have a loader for scene configuration file in JSON, the scene will only be fully loaded  <br/>
 * after all its dependencies are loaded, then you will need to use function to flow in all dependencies  <br/>
 * found in the configuration file, and finish the loader pipe only after all dependencies are loaded (in the callback).
 * !#zh
 * 让新 items 流入 pipeline 并且当 item 列表完成时进行回调函数。<br/>
 * 这个 API 的使用通常是为了加载依赖项。<br/>
 * 例如：<br/>
 * 我们需要加载一个场景配置的 JSON 文件，该场景会将所有的依赖项全部都加载完毕以后，进行回调表示加载完毕。
 * @method flowInDeps
 * @deprecated since v1.3
 * @param {Array} urlList
 * @param {Function} callback
 * @return {Array} Items accepted by the pipeline
 */
proto.flowInDeps = function (owner, urlList, callback) {
    var deps = LoadingItems.create(this, function (errors, items) {
        callback(errors, items);
        items.destroy();
    });
    return deps.append(urlList, owner);
};

proto.flowOut = function (item) {
    if (item.error) {
        delete this._cache[item.id];
    }
    else if (!this._cache[item.id]) {
        this._cache[item.id] = item;
    }
    item.complete = true;
    LoadingItems.itemComplete(item);
};

/**
 * !#en
 * Copy the item states from one source item to all destination items. <br/>
 * It's quite useful when a pipe generate new items from one source item,<br/>
 * then you should flowIn these generated items into pipeline, <br/>
 * but you probably want them to skip all pipes the source item already go through,<br/>
 * you can achieve it with this API. <br/>
 * <br/>
 * For example, an unzip pipe will generate more items, but you won't want them to pass unzip or download pipe again.
 * !#zh
 * 从一个源 item 向所有目标 item 复制它的 pipe 状态，用于避免重复通过部分 pipe。<br/>
 * 当一个源 item 生成了一系列新的 items 时很有用，<br/>
 * 你希望让这些新的依赖项进入 pipeline，但是又不希望它们通过源 item 已经经过的 pipe，<br/>
 * 但是你可能希望他们源 item 已经通过并跳过所有 pipes，<br/>
 * 这个时候就可以使用这个 API。
 * @method copyItemStates
 * @param {Object} srcItem The source item
 * @param {Array|Object} dstItems A single destination item or an array of destination items
 */
proto.copyItemStates = function (srcItem, dstItems) {
    if (!(dstItems instanceof Array)) {
        dstItems.states = srcItem.states;
        return;
    }
    for (var i = 0; i < dstItems.length; ++i) {
        dstItems[i].states = srcItem.states;
    }
};

/**
 * !#en Returns an item in pipeline.
 * !#zh 根据 id 获取一个 item
 * @method getItem
 * @param {Object} id The id of the item
 * @return {Object}
 */
proto.getItem = function (id) {
    var item = this._cache[id];

    if (!item)
        return item;

    // downloader.js downloadUuid
    if (item.alias)
        item = item.alias;

    return item;
};

/**
 * !#en Removes an completed item in pipeline.
 * It will only remove the cache in the pipeline or loader, its dependencies won't be released.
 * cc.loader provided another method to completely cleanup the resource and its dependencies,
 * please refer to {{#crossLink "loader/release:method"}}cc.loader.release{{/crossLink}}
 * !#zh 移除指定的已完成 item。
 * 这将仅仅从 pipeline 或者 loader 中删除其缓存，并不会释放它所依赖的资源。
 * cc.loader 中提供了另一种删除资源及其依赖的清理方法，请参考 {{#crossLink "loader/release:method"}}cc.loader.release{{/crossLink}}
 * @method removeItem
 * @param {Object} id The id of the item
 * @return {Boolean} succeed or not
 */
proto.removeItem = function (id) {
    var removed = this._cache[id];
    if (removed && removed.complete) {
        delete this._cache[id];
    }
    return removed;
};

/**
 * !#en Clear the current pipeline, this function will clean up the items.
 * !#zh 清空当前 pipeline，该函数将清理 items。
 * @method clear
 */
proto.clear = function () {
    for (var id in this._cache) {
        var item = this._cache[id];
        delete this._cache[id];
        if (!item.complete) {
            item.error = new Error('Canceled manually');
            this.flowOut(item);
        }
    }
};

cc.Pipeline = module.exports = Pipeline;