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State Chart XML Classes(3) | Coin | State Chart XML Classes(3) |
NAME¶
State Chart XML Classes -Classes¶
class ScXML
Detailed Description¶
This set of classes is a basic implementation of State Chart XML. It is not complete, nor is it necessary conformant to those parts it implements. It is however a decent start, and there are plans for implementing more parts of the specification. Currently Coin uses SCXML for managing 3D viewer user interaction (the non-model-interaction part) - the examiner navigation mode in layman terms - but with a more complete implementation of SCXML, the potential for more uses should be quite huge. The Draft Specification for SCXML is at http://www.w3.org/TR/scxml/. Since:Coin 3.0
State Chart XML The ScXML part of Coin is a basic, non-conformant,
partial implementation of State Chart XML, based on the W3C Working Draft 21
February 2007 of SCXML http://www.w3.org/TR/2007/WD-scxml-20070221/. Read that
document for a basic understanding how SCXML documents should be constructed.
NOTE: A new version of the draft has just been released (May 2008). The code
here does not reflect any changes done to the draft SCXML specification yet.
Coin uses it for its navigation system, to be able to remove hardcoded logic for
user navigation and externalize it into XML files. It is hoped that this
technology will prove to be a useful addition to Coin and get broader use as
this subsystem matures. The dragger and manipulator user interaction logic is
likely one area where ScXML might be employed later. Attaching state
machines to interactive parts of the scene graph could be another interesting
idea for the future.
For now, the ScXML system is not employed in any pre-established Coin
usage patterns, and you will need to employ new features to touch base with
it. The most obvious are where ScXML will be used is if you use Quarter
1.0 over Coin 3.0, as you manipulate the camera movements around the 3D models
through mouse and keyboard interaction.
The Coin type system makes it possible to override the default types to have the
state chart description instantiated using customized objects. A design choice
made in that regard was to both use the type overriding system in Coin, and
also to use the 'xmlns' (XML Namespace) attribute to make ScXML types
available and to prioritize which classtypes to instantiate objects from. The
xmlns attribute is currently only checked at the document level, but the plan
is to let any state have this attribute, and to simulate static scoping rules
for namespace prioritization.
Partially Supported Items:
- •
- At the moment, the Coin ScXML module only supports
'Executable
Content' through the <invoke> element, using the ScXMLInvoke class interface and having the Executable Content written in C++ in subclasses of the ScXMLInvoke class. ECMAScript and XPath is not supported yet.
- •
- External document referencing through the <state> / <parallel> 'src' attribute is not yet handled, but should be easy to implement so it will likely be one of the first things that will be fixed.
- •
- The <parallel> element is not supported as intended with parallel states. Coin will just treat it as an ordinary <state> element for now. Parallel states is not high up on the priority list, so expect this to be handled after a lot of other functionality is in place.
- •
- The <datamodel>-related part of the specification is not supported.
- •
- The condition attribute in the <transition> element is not supported, so the only condition you can set is on the event type in the event attribute. The ScXMLTransition class has a virtual method SbBool evaluateCondition() which is used in the state machine logic, and should be all that is needed to overload to implement this in subclasses yourself.
- •
- The 'target' attribute in the <transition> element can only identify a single state currently, not multiple as you would have to when having support for <parallel> elements (which we don't have).
- •
- The virtual state elements like <history> and <anchor> are just implemented as dummy states for now and do not do anything in relation to what they should actually do.
- •
- There are no mechanisms for inter-statemachine event passing yet.
Coin 3.0
Author¶
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