Other Features

Segments are dynamic; that is, they can be created or destroyed, can grow or shrink, or can be modified. A segment can be opened at any time while the display list exists. While a segment is open, elements (geometric primitives, attributes, control functions, etc.) can be added to, deleted from, or replaced in the segment.

Individual elements can be displayed while they are being placed into a segment, or as an entire segment network is displayed. Explicit display traversal, distinct from segment creation or editing, gives an application the option of making a set of modifications to a segment network, and then displaying the complete result.

Particular portions of a segment network can be identified through the picking operation. Picking identifies an object indicated by the user, typically through an input device such as a mouse or a tablet. Pick traversal, like display traversal, is explicitly invoked for a segment network giving the application control over when this traversal takes place.

Filtering functions are provided to selectively control the display and pick traversal processes, as well as primitive highlighting. These functions allow the depth of traversal to be limited and also allow portions of the segment network to be excluded from the traversal process. This effectively makes parts of the segment network invisible, unpickable, or highlighted.

Application data can be placed into a segment and inquired from a segment, thereby providing applications the ability to relate the graphics data stored in the display list to their application models.

A "pruning" functionality allows applications to skip entire branches of a hierarchy if the primitives therein would not affect the image; for example, if all the primitives would draw outside the clip limits.

A "culling" functionality is provided to allow an application to select between multiple representations of parts of images. Suppose, for example, you have a very detailed architectural image of a building. All major systems are shown, as well as very fine detail of all those systems. When you zoom out away from the building, to get a "big picture" look at it, the extremely fine detail does nothing but increase the rendering time; your display does not have the resolution to even see such small things. To address this, Display List allows you to display a more detailed rendering when up close, but a less detailed (and faster-executing) rendering when far away.