An application draws by calling graphics functions. Applications store retained graphics in segments, which can be edited. This means that the retained image can be modified without having to re-create the unmodified portion using multiple GPI functions.

When using nonretained graphics, the output appears on the output device (for example, a window) immediately. However, if part of the picture is erased or must be repeated, the application must call the same graphics functions a second, or even a third time.

There are many other advantages to using retained graphics, including:

• Convenience-An application can draw retained graphics with a single function that accesses the storage area containing all the individual functions necessary for the object.

• Flexibility-An application can redraw graphics retained in the segment store to any number of device contexts.

• Editing-An application can modify an object without having to call all the functions necessary to re-create the picture. Individual segments can be moved, scaled, or rotated; then, redrawn.

  Editing the graphics within a segment is described in Editing Retained Graphics and Graphics Segments.

• Power-An application can access the more powerful and useful graphics functions only when graphics are stored in segments.

• Organization-An application can use segments to store the components that will be assembled into the final picture.

Primarily, a graphics segment is a means of grouping and storing graphics primitives and their attributes. Although the graphics within a segment usually are related in some way, they do not have to be. A segment might contain a number of unrelated GPI functions that you want to keep and execute at specific times.

Retained graphics do affect application performance, however, in that a normal presentation space requires 114KB of main memory more than a micro presentation space, and using the drawing mode DM_RETAIN adds an additional 46KB.

Note: Your application can have up to 16KB (16378) segments in the segment store of a single presentation space. The size of an individual segment is limited only by the amount of storage available to you.

Do not confuse a graphics segment with a memory segment.