The hallmark of scene graph systems is that they facilitate rapid applications development. All graphics applications, whether they use a scene graph system or not, must manage data. The objects to be drawn must be stored somewhere, and must be dispatched to a renderer in a more or less sequential fashion. The data storage, management and access machinery is fundamental part of scene graph systems. Use of this existing machinery is a convenience, and use of this machinery relieves applications developers of the burden of creating and maintaining this central part of a graphics application.

In addition to the data management infrastructure, additional convenience comes in the form of management of intricacies and details. A complex scene in three dimensions contains many different elements, including light sources, a camera model used to view the scene, objects in the scene, and so forth. Additional details that might escape a quick glance include clipping planes, a mechanism for clearing the color and depth buffers at the start of each frame, viewport controls. Keeping track of all this information, along with providing reasonable defaults, can be vastly simplified by a good scene graph system.

How Many Widgets?

One of the roles of graphics subsystems, such as OpenGL, and graphics hardware is to provide the means to quickly draw objects. Graphics hardware excels at drawing simple objects, such as triangles and line segments. However, graphics hardware is typically not known for its ability to draw more complicated objects, such as polyhedra or spheres. Polyhedra are collections of polygons, while spheres are implicit surfaces with no direct geometric representation. Scene graph systems can store polyhedron data, and feed individual polygons or polygon groups to the graphics hardware. Similarly, spheres can be tessellated into collections of triangles that approximate the implicit surface. Tessellations can be coarse if the viewer is far away from the sphere or if the sphere projects down to a small number of pixels. Scene graph systems can provide numerous primitives above and beyond the set directly supported by the graphics hardware.