OGRE
1.11.6
Object-Oriented Graphics Rendering Engine
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Resources are data objects that must be loaded and managed throughout an application. A Ogre::Resource might be a Ogre::Mesh, a Ogre::Texture, or any other piece of data - the key properties are
A Ogre::ResourceManager is responsible for managing a pool of resources of a particular type. It must index them, look them up, load and destroy them. It may also need to stay within a defined memory budget, and temporarily unload some resources if it needs to to stay within this budget.
Resource managers use a priority system to determine what can be unloaded, and a Least Recently Used (LRU) policy within resources of the same priority.
Resources can be loaded using the generalised load interface, and they can be unloaded and removed. In addition, each subclass of ResourceManager will likely define custom 'load' methods which take explicit parameters depending on the kind of resource being created.
A resource is created in LOADSTATE_UNLOADED, it then progressed to LOADSTATE_PREPARED, the meaning of which depends on the concrete Resource type, but usually means that data has been read from disk into memory. LOADSTATE_LOADED means all data has been uploaded to the GPU and is ready to use without further processing.
Resources can be loaded and unloaded through the Ogre::Resource class, but they can only be removed (and thus eventually destroyed) using their parent Ogre::ResourceManager.
Resource files need to be loaded from specific locations. By calling Ogre::ResourceGroupManager::addResourceLocation, you add search locations to the list. Locations added first are preferred over locations added later. Furthermore locations are indexed at the time you add them, so make sure that all your assets are already there - or you will have to remove and re-add the location.
Locations can be folders, compressed archives, even perhaps remote locations. Facilities for loading from different locations are provided by plugins which provide implementations of the Ogre::Archive class. All the application user has to do is specify a 'loctype' string in order to indicate the type of location, which should map onto one of the provided plugins. Ogre comes configured with the FileSystem
(folders) and Zip
(archive compressed with the pkzip / WinZip etc utilities) types.
Resource Locations are organized in Groups. A resource group allows you to define a set of resources that can be loaded / unloaded as a unit. For example, it might be all the resources used for the level of a game.
You can create additional groups so that you can control the life of your resources in whichever way you wish.
Once you have defined a resource group, resources which will be loaded as part of it are defined in one of 2 ways:
After creating a resource group, adding some resource locations, and perhaps pre-declaring some resources, but before you need to use the resources in the group, you must call Ogre::ResourceGroupManager::initialiseResourceGroup to initialise the group. By calling this, you are triggering the following processes:
So what this essentially does is create a bunch of unloaded Ogre::Resource objects in the respective ResourceManagers based on scripts, and resources you've pre-declared. That means that code looking for these resources will find them, but they won't be taking up much memory yet, until they are either used, or they are loaded in bulk using Ogre::ResourceGroupManager::loadResourceGroup. Loading the resource group in bulk is entirely optional, but has the advantage of coming with progress reporting as resources are loaded.
Failure to call Ogre::ResourceGroupManager::initialiseResourceGroup means that Ogre::ResourceGroupManager::loadResourceGroup will do nothing, and any resources you define in scripts will not be found. Similarly, once you have called this method you won't be able to pick up any new scripts or pre-declared resources, unless you call Ogre::ResourceGroupManager::clearResourceGroup, set up declared resources, and call this method again.
inGlobalPool=true
at Ogre::ResourceGroupManager::createResourceGroup for all groups that should be able to cross-reference resources.Declaring the resources you intend to use in advance is optional, however it is a very useful feature. By declaring resources before you attempt to use them, you can more easily control the loading and unloading of those resources by their group. Declaring them also allows them to be enumerated, which means events can be raised to indicate the loading progress (Ogre::ResourceGroupListener).
To declare a resource use Ogre::ResourceGroupManager::declareResource. This is useful for scripted declarations since it is entirely generalised, and does not create Resource instances right away. This adds the following conceptual stages before a Resource is created as Unloaded: