Asset Manifest & Asynchronous Asset Loading

A graphical application usually depends on tons of assets (textures, models, etc) to process and render. It is usually not possible deploy all assets to client machine at installation time, instead assets are downloaded from the server usually on first use.

NPL/ParaEngine has built-in support for asynchronous asset loading via asset manifest system. Basically it resolves two problems:

1. Use a plain text file to look up and download assets in the background in several worker threads.
2. Most UI and 3d objects in ParaEngine provide a synchronous interface to set assets, as if they are already available. In reality, they will automatically resolves assets (also their dependencies) when those assets are available locally.

Asset Manifest Manager

When an application starts, NPLRuntime will read all Assets_manifest*.txt file under the root directory. Each file has following content

    format is [relative path],md5,fileSize 

if the name ends with .z, it is zipped. This could be 4MB uncompressed in size md5 is checksum code of the file. fileSize is the compressed file size.

    audio/music.mp3.z,3799134715,22032
    model/building/tree.dds.z,2957514200,949
    model/building/tree.x.z,2551621901,816
    games/tutorial.swf,1157008036,171105

When one of the async loader try to load an application asset(texture, model, etc), it will first search in AssetManifest using the TO-LOWER-CASED asset path, such as (model/building/tree.x). if will then search the “temp/cache/” directory for a matching file

The file matching is done by comparing the line in the asset file with the filename in the cache directory, using their md5 and size.

    audio/music.mp3.z,3799134715,22032 matches to file 379913471522032

Example Usage:

    AssetFileEntry* pEntry = CAssetManifest::GetSingleton().GetFile("Texture/somefile.dds");
    if(pEntry && pEntry->DoesFileExist())
    {
        // Load from file pEntry->GetLocalFileName();
    }