Optional Parameters

Author: Santy-Wang, Xunyi

For added flexibility and extensibility, most of the load interfaces in Asset Manager, including cc.assetManager.loadAny and cc.assetManager.preloadAny, provide options parameters. In addition to configuring the built-in parameters of Creator, options also allows you to customize any parameters to extend engine functionality. If you do not need to configure the engine's built-in parameters or extend the engine's functionality, you can ignore it and just use the simpler API interfaces, such as cc.resources.load.

Parameters that are currently used by the engine in options include the following:

uuid, url, path, dir, scene, type, priority, preset, audioLoadMode, ext, bundle, onFileProgress, maxRetryCount, maxConcurrency, maxRequestsPerFrame, version, responseType, withCredentials, mimeType, timeout, header, reload, cacheAsset, cacheEnabled

Please DO NOT use the above fields as your custom parameter names to avoid conflicts with engine functions.

Control loading pipeline

The optional parameters serve as a communication tool between the upper level business logic and the lower level load pipeline. The upper level business logic provides parameters to control the operation of the lower level load pipeline.

Controls downloader and parser

The optional parameters priority, maxConcurrency, maxRequestsPerFrame, maxRetryCount are used to control the downloader's prioritization of download requests, the limit on the number of concurrent loads, the limit on the number of requests that can be initiated per frame, and the maximum number of retries, respectively. For example:

cc.assetManager.loadAny({'path': 'image/background'}, {priority: 2, maxRetryCount: 10}, callback);

Controls the handler of downloader and parser

The handler for resources such as text files and binary files in the downloader/parser, accepting optional parameters responseType, withCredentials, mimeType, timeout, header, onFileProgress to set the XHR's return type, header, download progress callback and other parameters.

// Get a download progress callback for XHR
cc.assetManager.loadAny({'path': 'image/background'}, {onFileProgress: function (loaded, total) {
    console.log(loaded/total);
}}, callback);

While the optional parameter audioLoadMode controls whether or not the audio file's handler uses WebAudio to load audio.

// Load audio remotely using WebAudio.
cc.assetManager.loadRemote('http://example.com/background.mp3', {audioLoadMode: cc.AudioClip.LoadMode.WEB_AUDIO}, callback);

Note: loading progress of the resources must be configured on the server if you want to get it.

For more information about the handler, please refer to document Download and Parse.

Control loading process

The optional parameters reload, cacheAsset, and cacheEnabled are used to control the loading pipeline whether to reuse the resources in the cache, whether to cache the resources, and whether to cache the files.

cc.assetManager.loadRemote(url, {reload: true, cacheAsset: false, cacheEnabled: true}, (err, asset) => {});

While the optional parameters uuid, url, path, dir, scene, type, ext, bundle, etc. are used to search for resources.

cc.assetManager.loadAny({'path': 'images/background', type: cc.SpriteFrame, bundle: 'resources'}, callback);

cc.assetManager.loadAny({'dir': 'images', type: cc.SpriteFrame, bundle: 'resources'}, callback);

This approach is exactly equivalent to using cc.resources.load and cc.resources.loadDir directly.

Engine Extension

You can extend the loading capabilities of the engine by using optional parameters in the Pipeline and Custom Handlers. For example:

// Extend the pipeline
cc.assetManager.pipeline.insert(function (task, done) {
    var input = task.input;
    for (var i = 0; i < input.length; i++) {
        if (input[i].options.myParam === 'important') {
            console.log(input[i].url);
        }
    }
    task.output = task.input;
    done();
}, 1);

cc.assetManager.loadAny({'path': 'images/background'}, {'myParam': 'important'}, callback);

// Register the handler
cc.assetManager.downloader.register('.myformat', function (url, options, callback) {
    // Download the resource
    var img = new Image();
    if (options.isCrossOrigin) {
        img.crossOrigin = 'anonymous';
    }

    img.onload = function () {
        callback(null, img);
    };

    img.onerror = function () {
        callback(new Error('download failed'), null);
    };

    img.src = url;

});

cc.assetManager.parser.register('.myformat', function (file, options, callback) {
    // Parse the downloaded file
    callback(null, file);
});

cc.assetManager.loadAny({'url': 'http://example.com/myAsset.myformat'}, {isCrossOrigin: true}, callback);

The engine can be extremely extensible by using optional parameters, combined with pipelines and custom handlers, and Asset Bundle can be seen as the first instance of extension using optional parameters.