| | Application Interactive Services provide the means to
create links between an application GUI viewer and
the packages which are used to manage selection
and presentation. The tools AIS defined in order to
do this include different sorts of entities: both the
selectable viewable objects themselves and the
context and attribute managers to define their
selection and display.
To orient the user as he works in a modeling
environment, views and selections must be
comprehensible. There must be several different sorts
of selectable and viewable object defined. These must
also be interactive, that is, connecting graphic
representation and the underlying reference
geometry. These entities are called Interactive
Objects, and are divided into four types:
- the Datum
- the Relation
- the Object
- None.
The Datum groups together the construction elements
such as lines, circles, points, trihedra, plane trihedra,
planes and axes.
The Relation is made up of constraints on one or
more interactive shapes and the corresponding
reference geometry. For example, you might want to
constrain two edges in a parallel relation. This
contraint is considered as an object in its own right,
and is shown as a sensitive primitive. This takes the
graphic form of a perpendicular arrow marked with
the || symbol and lying between the two edges.
The Object type includes topological shapes, and
connections between shapes.
None, in order not to eliminate the object, tells the
application to look further until it finds an object
definition in its generation which is accepted.
Inside these categories, you have the possibility
of an additional characterization by means of a
signature. The signature provides an index to the
further characterization. By default, the Interactive
Object has a None type and a signature of 0
(equivalent to None.) If you want to give a particular
type and signature to your interactive object, you must
redefine the two virtual methods: Type and Signature.
In the C++ inheritance structure of the package, each
class representing a specific Interactive Object
inherits AIS_InteractiveObject. Among these
inheriting classes, AIS_Relation functions as the
abstract mother class for tinheriting classes defining
display of specific relational constraints and types of
dimension. Some of these include:
- display of constraints based on relations of
symmetry, tangency, parallelism and concentricity
- display of dimensions for angles, offsets,
diameters, radii and chamfers.
No viewer can show everything at once with any
coherence or clarity. Views must be managed
carefully both sequentially and at any given instant.
Another function of the view is that of a context to
carry out design in. The design changes are applied
to the objects in the view and then extended to the
underlying reference geometry by a solver. To make
sense of this complicated visual data, several display
and selection tools are required. To facilitate
management, each object and each construction
element has a selection priority. There are also
means to modify the default priority.
To define an environment of dynamic detection, you
can use standard filter classes or create your own. A
filter questions the owner of the sensitive primitive in
local context to determine if it has the the desired
qualities. If it answers positively, it is kept. If not, it is rejected.
The standard filters supplied in AIS include:
AIS_AttributeFilter
AIS_SignatureFilter
AIS_TypeFilter.
Only the type filter can be used in the default
operating mode, the neutral point. The others can
only be used in open local contexts.
Neutral point and local context constitute the two
operating modes of the central entity which pilots
visualizations and selections, the Interactive Context.
It is linked to a main viewer and if you like, a trash bin
viewer as well.
The neutral point, which is the default mode, allows
you to easily visualize and select interactive objects
which have been loaded into the context. Opening
local contexts allows you to prepare and use a
temporary selection environment without disturbing
the neutral point. A set of functions allows you to
choose the interactive objects which you want to act
on, the selection modes which you want to activate,
and the temporary visualizations which you will
execute. When the operation is finished, you close the
current local context and return to the state in which
you were before opening it (neutral point or previous
local context).
An interactive object can have a certain number of
graphic attributes which are specific to it, such as
visualization mode, color, and material. By the same
token, the interactive context has a set of graphic
attributes, the Drawer which is valid by default for the
objects it controls. When an interactive object is
visualized, the required graphic attributes are first
taken from the object's own Drawer if one exists, or
from the context drawer for the others.
More...
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1.6.3