GEOS SDK TechDocs
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4.4 The Vis Class Tree
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4.6 Working with Visible Object Trees
You can create a visible object tree either in your Goc source code or at run-time. As stated earlier, the visible tree is linked to the generic UI object tree through the GenView object. Without a view object, you will not be able to display your visible objects.
The visible object tree must have a
VisContentClass
object (or a subclass of
VisContentClass
) as its root object. If another class is chosen for the topmost object, that class will have to handle all the messages that would normally be received by a content; otherwise, results are unpredictable and your application will likely not function the way you expect.
VisContent objects are rarely, if ever, used lower in the visible tree than as the top node. For levels further down in the tree, you can use
VisCompClass
(or, again, a subclass of
VisCompClass
). VisComp allows the object to have children and does not incur the same amount of overhead associated with a VisContent. Any object in the visible tree that may have children must be a "composite" object, or a subclass of
VisCompClass
.
Leaf nodes of the visible tree can be direct subclasses of
VisClass
. Objects of
VisClass
can not have children, but they have all the attributes and instance data you need for a leaf node. You must subclass
VisClass
, however, if your object is ever to be shown on the screen: Since visible objects can have any application-defined visible representation, you must write the
MSG_VIS_DRAW
handler yourself; this can be done only in a subclass.
GEOS SDK TechDocs
|
| 4.4 The Vis Class Tree
| 4.6 Working with Visible Object Trees