About Creating and Drawing Retained Graphics

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.