DOM code generator

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Summary: The COLLADA DOM code generator is an external application that is used to generate the C++ classes that are used in the COLLADA DOM.

Obtaining the code generator

The code generator comes with the DOM itself, in the codeGen folder. A readme is provided that explains how to run the code generator.

DOM generated types

DOM type information is stored in:

  • daeTypes.h, the DOM's basic types
  • daeDomTypes.h, mappings from XML Schema basic types to DOM types
  • domTypes.h types generated by the code generator

Any other new types defined in the COLLADA schema document generate new atomic types or add name bindings to existing atomic types in the DOM. All types defined in the COLLADA schema are restrictions, extensions, unions, or lists of existing types.

Type declaration formats

For what Format
most type declarations
typedef base_type_name domNew_type_name 
list types
typedef daeTArray< base_type_name > domNew_type_name
enum types
enum domNew_type_name

Each enum value is then created as NEW_TYPE_NAME_Enum

union types Supported only for unions of enums. A new enum is generated for that union type containing the symbols and values of all enums contained in the union.

Code for registered types

All generated types are registered in the registerDomTypes function found in domTypes.cpp. For all types except enums, code is generated that looks like

type = daeAtomicType::get("base_type_name");
   if ( type == NULL ) { //register as a raw type
      type = new daeRawRefType;
       type->_nameBindings.append("new_type_name");
           daeAtomicType::append( type );  
       }
   else { //add binding to existing type
       type->_nameBindings.append("new_type_name ");
       }

This code searches for a type for the base_type_name. If it finds one, it adds new_type_name as a name binding for that type. If the base type does not exist then a new rawRefType is created.

Enumerated types

A new type is always generated for enums. The arrays _strings and _values are populated with the enum values. In the schema, if an enumeration has an <xs:annotation> with an <xs:appinfo> value=value, the enum created will have a value value.

DOM-generated classes

Interface

Each <xs:element>, <xs:group>, and <xs:complexType> generates a new daeElement subclass name domElement_name.

Each attribute and child element and a value (if it has one) gets its data storage and accessor and mutators. Array types and URIs are returned by reference. All other types are returned by value.

If an element has an <xs:choice> content model group and more than a single child element, it will have _contents, _contentsOrder, and _CMData arrays to store the data needed to represent the ordering of children in the content model.

An <xs:complexType> generates two classes:

  • The class description/interface.
  • A daeElement subclass that inherits from both daeElement and the new class interface.

Any class defined in XMLSchema global scope (not defined as a child of another element) generates a new daeElement subclass. This new element, if the type attribute is a complex type, also inherits from the complex type interface and daeElement.

An element that is part of a substitution group inherits from the element it is substitutable for. Then the DOM uses polymorphism and stores a pointer to the base class, which could be an object of any of the substitutable classes.

The code generator allows for schema type inheritance by either extension or restriction. In either case, the new class inherits from the base class. Restriction is handled with the DOM meta information because C++ can do inheritance only by extension. The current (COLLADA 1.4.1) schema does not take advantage of this feature.

The code generator allows for scoped type definitions. This happens when a simple type is created anonymously in the schema document instead of creating a global simple type and referencing it. The current (COLLADA 1.4.1) schema does not take advantage of this feature.

When generating mutators for string data attributes or values, the generator creates code:

*(daeStringRef*)&attrAttribute_name = atAttribute_name 

which lets the DOM create memory to store its string data.

The xmlns attribute is created only for elements that have an <xs:annotation> <xs:appinfo> that contains enable-xmlns.

Meta generation

Each element that is generated has a function registerElement. This is the function that is called to create the meta information that describes the new element.

Every element’s _Meta descriptor has a name and a pointer to the element’s creation function create(daeInt bytes).

If the new element is created from an <xs:group> then the meta is tagged as transparent. Transparent means that the IOplugin will not create an XML tag or any attributes for this element when it is saved. Essentially, the transparent flag means that the element exists in the COLLADA DOM content but doesn’t really exist in the XML content.

If the new element is abstract, the abstract flag is set for the meta. Abstract elements cannot be placed in the DOM.

If the element is not declared in the schema’s global scope then the isInnerClass flag is set to true. This flag is used by the metaAny content model group. Any globally declared elements can be created as part of the “any” content model, but elements declared as inner classes can not. Any other children of an “any” group become the weakly typed domAny elements.

Each attribute has a new metaAttribute or metaArrayAttribute created to describe it. This metaAttribute is given a name, a type, and the pointer offset into the class where the data can be found. If the attribute is marked required or given a default value, that is also set on the metaAttribute.

When a COLLADA element can have character content, the content is usually stored in a variable called _value in the corresponding DOM class. This value is treated the same as a normal attribute.

The metaCMPolicy object tree is generated to match the content model specified in the schema. Only the xs:any content model group is not supported.

Any content model that contains either an element that is the base for a substitution group or both a choice and more than one child element will have contents and contentsOrder metaAttributes added.

If the element’s content model contains an xs:choice group then the meta will have a CMData metaAttribute created.

Code generator program flow and systems

The code generator is run by starting gen.php with a php interpreter. Arguments include:

schema_name The schema to use for code generation. Required.
min (after the schema) Generate the minimal integration classes. By default, the generator creates the full integration classes.
cprt Use the SCEA Shared Source License copyright as the header. This is the way the generated classes should be created. By default, the generator puts the SCEA SNIP copyright as the header of all of the files.

So, for example, you might run

gen.php colladaSchema14.xsd cprt

The generator does the following:

  1. Parses the schema document and creates its own DOM-like structure to store the info from the schema.
  2. For each schema element that might be encountered, there needs to be a source file xsElementName.php. This class is used to store the data related to that element. The source file needs to be included (require_once in PHP) in the object-model.php file.

((EDITOR: This page needs the following improvement: the preceding isn't really a step...need to convert ))

  1. Each of the object model classes has a constructor that registers what elements and attributes (along with their min and maxOccurs) are valid for that element.

((EDITOR: This page needs the following improvement: ditto ))

  1. The SchemaParser class uses the default PHP SAX XML parser to parse the schema document and create the custom DOM used for code generation.
  2. Gets all elements that are xs:simpleType and calls generate on them, which in turn creates a TypeMeta object that contains the data needed to generate the COLLADA simple types.
  3. Does the same for <xs:complexType>, <xs:group>, and <xs:element>.

The template-engine source file contains the logic on how to apply a template. Templates suffixed with –file, contain the logic for creating a new C++ source or header file and applying another template to actually write the C++ code.

The most significant templates are:

  • tpl-types-header.php for generated type definitions
  • tpl-types-cpp.php for type registration
  • tpl-class-def.php for generated class interfaces
  • tpl-cpp-methods for the generation of the meta for each class.


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
Additional information:  • What's new  • Backward compatibility  • Future work
Terminology categories:  • COLLADA  • DOM  • XML