Extension
COLLADA provides flexibility by allowing applications to define extensions to existing COLLADA elements. These extensions take the form of alternative <technique> elements, additive <extra> elements, and scalable <input> elements.
Extension by Alternative
COLLADA enables multirepresentation of many of its elements; that is, an element can contain multiple representations of its meaning, each relevant to a different environment. In such cases, the element is defined using one required <technique_common> and zero or more <technique> elements:
- The common technique is a representation of the element that is strongly typed in the schema.
- Other techniques are defined by the vendor supplying the alternative representation. Each <technique> has a profile attribute that specifies the platform (product name or similar) to which the extension applies.
Each alternative representation of an extensible element should contain values that describe the element for that profile. The representations may have coherency between profiles, although that is not required. In other words, if <technique_common> describes an ambient light, an alternative <technique> for that light could validly describe something else, such as an area light for the specified profile.
Using <technique> to choose profiles
A COLLADA processor will choose either one, and only one, of the available alternatives. It will choose the <technique_common> or one of the <technique> elements. Where alternative choices are possible within the schema, the <technique> element models the alternative extensions. For example:
<light>
<technique_common>
<ambient>
<color/>
</ambient>
</technique_common>
<technique profile="alternative_1"/>
<technique profile="alternative_2"/>
</list>