About Metafiles

Metafiles can exist in three distinct forms. A metafile that has just been created is called a memory metafile because it exists in memory managed by the Presentation Manager on behalf of the application that created it. A metafile that is transferred to disk storage as a file with the default extension of .MET is called a disk metafile. A metafile that is loaded into an application's memory is editable by the application.

Metafiles save resources in the following ways:

• Metafiles can be created and used in draw mode by a single application. Therefore, an application that is not retaining segments in a segment store can retain graphics in a metafile.

• Metafiles remain available while the owning application is running, regardless of the number of presentation spaces the application obtains or defines.

• Given the same starting conditions in each presentation space, you can produce an identical picture each time the metafile contents are executed.

• Different threads or processes within an application can display a picture stored as a metafile without each having to own the metafile.

• If your organization has common graphical resources, such as a company logo, those resources can be stored in a metafile. This avoids the overhead of re-creating the resources each time they are needed.

• Because the metafile is a device-independent format, it is useful for transferring pictures that are to be printed when the printer-type is unknown.

• PM applications can exchange graphical information by using metafiles, either by using the clipboard or by transferring them over a network.

• Your application can also exchange graphics data with non-PM applications that support the Mixed Object Document Content Architecture (MO:DCA) interchange standard.

Unlike bit-maps, metafiles offer some device-independence. Bit maps store picture information on a pel-by-pel basis. Metafiles store picture information in the form of low-level graphics commands that the operating system uses to construct the pictures.

Note: Metafiles can contain bit maps or other graphics information that is in device-dependent format.

The graphics commands, called "graphics orders", represent graphics functions that create a picture. These include drawing instructions, as well as attribute-setting instructions (for example, color tables and logical fonts) and anything that describes the structure of the picture. The contents of a metafile, therefore, are similar to those of the graphics presentation space in which the picture is drawn. The Presentation Manager automatically records the environmental detail of the presentation space in which a picture is drawn in the metafile.

Note: A metafile can contain data generated from GPI functions only. Any non-graphical data included in a metafile is ignored.

An application can re-create a picture from a metafile and display it in a window on the screen or print it by "playing" the metafile. When an application displays the contents of a metafile, it can use the color table, font, fill pattern, and transformations that are stored in the metafile, or it can use the logical color table, logical font, fill pattern, and transformations that are set for the current presentation space. The appearance of the picture stored in the metafile can, therefore, be changed by editing the current presentation space before playing the metafile.

An application can save metafiles to a disk to be loaded later by any application that chooses to access the metafile. Disk metafiles loaded into application memory can also be edited in the same manner as elements in graphics segments are edited.

They contain both primitives and attributes.