Scene

Files:	Scene.h, Scene.C
Derived from:	\bf PickList
Global instance (if any):	scene
Used in optional component:	Part of main VMD code

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.

Constructors

• Scene::Scene(void)

Internal data structures

• int numDisplayable2D, numDisplayable3D - the number of 2D and 3D Displayable's which have registered. Derived classes maintain the actual lists.

• int numCmdLists2D, numCmdLists3D - the number of 2D and 3D display lists have been registered. Derived classes maintain the actual lists.

Virtual member functions

• virtual void prepare(DisplayDevice *) - goes through all the registered objects and prepares them for drawing. This should be called before draw.

• virtual void draw(DisplayDevice *) - actually draws the scene, using the given DisplayDevice. If this display is in stereo, this will first draw the left eye view, then the right.

• virtual int filedraw(char *, char *, DisplayDevice *) - very similar to draw, except this draws the scene to a file-based DisplayDevice. The first two arguments are the format, and the filename. The different formats and file-rendering objects are maintained by a global instance of the object FileRenderList.

Method of use

A Scene is created at the start of the program, and all Displayable objects should be added to that scene (or to another Displayable as a child). It is used in the primary event loop to prepare and draw all the Displayable's. It is also used to pick items with a pointer. The global routine VMDupdate contains an example of using a Scene object.

There are two derived classes from Scene:

• NormalScene - this is the basic version, which is used for every case except when the CAVE display device is being used. It uses standard memory allocation routines to create storage for display lists, and to store the lists of Displayables and display lists.

• CaveScene - this uses shared memory to store the display lists, so that the CAVE processes can all see the same data for rendering the scene.

Suggestions for future changes/additions

As mentioned for Displayable, the prepare routine could be modified to return a flag indicating whether anything has changed in the Displayable objects which would require a redraw. If nothing changed, then a redraw could be avoided.