Type & Object

A Type and an Object

When a user chooses an item in combo boxes NEW, SCENE, and PAR, the Status Bar displays a line with its short description.

The item names and their descriptions includes four elements:

Type-Name -- the symbolic name of the object type, as it appears in the drop down lists of combo boxes NEW and SCENE.

Type-Description -- the line that appears in the Status Bar to describe what the Type-Name means. It appears when the mouse pointer points to an item inside the drop down list of either the combo box NEW or the combo box SCENE.

Parameter-Name -- the symbolic name of the parameter, as it appears in the combo box PAR.

Parameter-Description -- the line that appears in the Status Bar to describe what the Parameter-Name means. It appears when the mouse pointer points to an item inside the drop down list of the combo box PAR.

The combo box NEW shows the list of available object types. A user can choose a Type-Name to add an object of this type to the 3D scene.

You can think of the combo box NEW as an "Object Factory" that manufactures objects of several types. When users choose an item in the combo box NEW, it means that they are ordering an object of a desirable type from the "Object Factory" (the combo box NEW). When users then click on the button "N", the order is being implemented, and the corresponding object is added to the 3D scene.

The combo box SCENE shows the list of objects in the particular scene that is currently active. Each object is denoted by its sequential number in the scene, and by its type. Therefore, in the combo box SCENE, the Type-Name appears after the sequential number of the object.

When an object in the scene (an item inside the combo box SCENE) is chosen, the combo box PAR becomes enabled. Users can open then the drop down list of the combo box PAR, and choose a parameter of the object that they would like to change.

The list of the available parameters that appears in the combo box PAR is predefined by the object type that was chosen in the combo box NEW before the object was created, but the particular values of these parameters belong to the particular object that is chosen in the combo box SCENE (not to the type that was chosen in the combo box NEW). In other words, the Type is a class, and the particular object in the scene is an instance (a particular case) of that class.

The Type predefines the parameters' list as a list of place holders for actual parameter values that will be filled when the object is created and added to the scene. When the "Object Factory" (the combo box NEW) issues an object, it assigns default values to its parameters. Then, when the object is added to the 3D scene, the user can change these values.

During all future transformations, the object remembers its Type. So each time users choose the object in the combo box SCENE and then open the combo box PAR, they find out what more can be done with this object.

This approach is a kind of parametric CAD. It provides a user with a flexible way to create and manipulate a scene, using a few basic object types. This mechanism allows users to maintain the initial designer's intention, newer losing the semantic information of the scene's composition.