Description

The Scene maintains and organizes a database with all the Displayable objects which are to be drawn by a DisplayDevice. It contains routines to add new Displayable's to its database, and to draw them to the screen or to a file. It is derived from PickList, and so maintains the information about what diffent picking modes are available, as well routines to pick an item with a pointer.

There are two different sets of lists stored by the Scene, with each list kept for both the 2D case and the 3D case. The lists are:

• Registered Displayable's; this list is used to prepare items to be drawn. Only top-level Displayable objects are kept in this list. When a Displayable is created, it registers itself with a Scene, and so gets added to this list.
• Registered display lists, the lists of drawing tokens created by Displayables. This list is used to actually draw the graphics, each item in this list represents one display list and is given to a DisplayDevice to be rendered.

This object also contains routines to apply a constant rotation to all Displayable's each time they are drawn, as well as to apply general transformations to all the items in the scene. The most important function of Scene is, however, to draw the scene to a display or to a file.