DOM resolver subsystem
Summary: The resolver subsystem manages the resolution of URIs based on a URI's scheme and filename extensions.
The resolver subsystem allows for custom URI resolvers to be written and added to the COLLADA DOM. These resolvers can be used to load various types of external references-- for example, binary representations of mesh data--or to provide access to different data systems--for example, using a database to access elements.
By default, the COLLADA DOM has only two resolvers:
- The main resolver,
daeLIBXMLResolver, resolves elements from COLLADA documents (.dae or .xml) with the file or http URI scheme. This can resolve elements from the same document or external document references.
- The newly added DOM raw resolver class,
daeRawResolver, resolves only .raw files with the file URI scheme.
Instantiating an object of a class that inherits from
daeURIResolver adds a custom resolver to the COLLADA DOM.
How it works
The base class
daeURIResolver contains a static array named
_KnownResolvers that contains resolvers. The constuctor for
daeURIResolver adds a reference to this to this list of resolvers. When a DOM URI class attempts to resolve itself, it searches through the
_KnownResolvers list for a resolver that matches its URI scheme and file extension. When an appropriate resolver is found, the resolver is then asked to resolve the current URI.
Related classes and functions
- DOM resolver class: An interface to inherit from for creating URI resolvers.
- DOM URI class: The class used to represent URIs in a COLLADA document.
DOM URI class
URI state – "empty" is a default constructed URI.
URI state - "loaded" is when there is a URI string but it hasn’t been normalized.
URI strings are parsed in
validate is the function that normalizes a URI string.
baseURI is constructed from the current working directory (cwd) (where available) when the
daeURI( int ) constructor is called.
daeElement container is the element that holds the
daeURI as either an attribute or value.
validate normalizes the URI string against one of (listed in priority):
- The URI string passed in as an argument
documentURI(taken from the container element if present)
- The static baseURI (cwd)
URI state – pending is after the URI is normalized but before it is resolved
validate is called when attempting to resolve the URI, in the copy constructor, when the
noFrag flag is true in the constructor, when attempting to makeRelativePath, during resolveURI.
The DOM always operates on fully normalized absolute URIs.
daeURIResolver attemptResolveElement (see below)
URI state – success, failed_unsupprted_protocol, failed_file_not_found, failed_id_not_found, failed_missing_containter, and failed_external_document are all valid states after
daeURIResolver base class
daeRawResolver inherit from
_KnownResolvers is a static list of current resolvers to use to attempt to resolve a URI.
The constructor for
daeURIResolver adds itself to the static list.
_loadExternalDocuments is the flag that a user can control for whether URI resolution will load documents.
attemptResolveURI is never called. It is dead.
attemptResolveElement iterates over the list of known resolvers and, if the protocol (URI scheme) and document extension are supported, it calls
resolveElement on the concrete resolver.
Future: This is a good system but the program flow should be structured differently. See DOM future work.
|COLLADA DOM - Version 2.4 Historical Reference|
|List of main articles under the DOM portal.|
|User Guide chapters: • Intro • Architecture • Setting up • Working with documents • Creating docs • Importing docs • Representing elements • Working with elements • Resolving URIs • Resolving SIDs • Using custom COLLADA data • Integration templates • Error handling|
Systems: • URI resolver • Meta • Load/save flow • Runtime database • Memory • StringRef • Code generator