DOM guide: Working with documents

This section describes how to load COLLADA instance documents into the COLLADA runtime database and how to save the runtime database into COLLADA instance documents.

Note: In some cases pointer and return value checks have been removed from this code for brevity.

Creating the DAE Object

To use the COLLADA DOM, your client code needs to include the following header files:

#include <dae.h>
#include <dom/domCOLLADA.h>

To use a specific effect profile, such as <profile_COMMON> or <profile_CG>, you must include the header for that profile. For example:

#include <dom/domProfile_CG.h>

A useful header to include is dom/domConstants.h. This provides constants for strings that are commonly used in the DOM. These strings include all the COLLADA element names and element type names. Many examples to follow use these constants.

After including the appropriate headers, your application needs to create a DAE object. The following example shows a DAE object created on the heap (using operator new) and accessed as a pointer.

DAE *collada_dom = new DAE();
// use the collada_dom variable
delete collada_dom;

You could also create the DAE object globally or on the stack.

URIs and File Paths

A common mistake is to pass a Windows or Linux file path to the DAE::load or DAE::save methods. Like COLLADA itself, the DOM uses URIs exclusively to reference resources or files. A file path needs to be converted to a file scheme URI before being passed to the COLLADA DOM. Below are some examples of converting a file path to a URI.

Example Description    File Path                        URI
Windows absolute path  C:\folder\file.dae               file:///C:/folder/file.dae
Windows relative path  ..\folder\file.dae               ../folder/file.dae
UNC path               \\remoteMachine\folder\file.dae  file://///remoteMachine/folder/file.dae
Linux absolute path    /folder/file.dae                 file:///folder/file.dae
Linux relative path    ../folder/file.dae               ../folder/file.dae

Loading COLLADA Documents

Use the DAE::load method to read an existing COLLADA document into the runtime database. When you load a document, the COLLADA DOM uses the document URI as the name of the document when searching or doing other operations where the document needs to be identified. In this example, the name of the document created by the load process is “file:///input_url_name.dae”, the same as the URI it was loaded from:

daeInt error = collada_dom->load("file:///input_url_name.dae");

The DAE::load method returns:

• DAE_OK if the load is successful.
• DAE_ERR_COLLECTION_ALREADY_EXISTS iff a document with the same name, or the same document, has already been loaded.
• DAE_ERR_BACKEND_IO for other errors encountered during load.

Note: The terms "collection" and "document" mean the same thing in the COLLADA DOM interface and documentation.

Creating New COLLADA Documents

You can use the COLLADA DOM to create a set of elements, add them to an empty database, and write the database to a COLLADA instance document. To do this, you need to ensure that you have a database created for use. When calling DAE::load or DAE::saveAs, the COLLADA DOM creates the default database and backend to use for those operations. If you start by creating data from scratch then you must ensure that there is a backend and a database created for use. This only needs to be done once per DAE object. To create and use the default database and backend, call

collada_dom->setDatabase(NULL);
collada_dom->setIOPlugin(NULL);

Now you're ready to create the document.

daeDocument *doc = NULL;
collada_dom->getDatabase()->insertDocument("file:///C:/Test/colladaDocument.dae", &doc);
// doc is now a valid COLLADA document

Unloading COLLADA Documents

If you want to release a document from memory you can use the DAE::unload method. The document to be unloaded is specified by its document URI name. This method returns either:

• DAE_OK upon success.
• DAE_ERR_COLLECTION_DOES_NOT_EXIST if the document does not exist in the runtime database.

It's only necessary to call DAE::unload if you want the document released from memory immediately. Otherwise, the document is automatically unloaded when the parent DAE object is destroyed.

Saving COLLADA Documents

After you have completed any changes to the elements in the database, you can write the contents of the database to a new URL using the DAE::saveAs method to save a specific document. You can use either the document name or the document index to choose which collection to save:

daeInt error = daeObject->saveAs("output_url_name.xml", "file:///input_url_name.xml");

To save the document to the same location that it was loaded from, use the DAE:save() method. This method has only two arguments; the first is either the document name or the document index. The second is an optional flag that specifies whether to overwrite any existing document. This flag defaults to true.

DAE::saveAs has three arguments. The first is the URI to save the document as. The second is either the document name or the document index. If this argument is omitted, the COLLADA DOM defaults to saving the first document that is currently in the runtime database. The last argument is an optional flag that specifies whether to overwrite any existing document. This flag defaults to true.

Note: The COLLADA DOM XML parser does not fully validate the data. It detects some types of errors in XML input but not all of them. You may want to run new COLLADA data through an XML validator before loading it into the DOM. If you are developing programs that write COLLADA data, you should run a validator on the output of your programs during testing.

See also

• DOM load and save flow