What Is a Windows Meta File?
Windows metafile is the native vector graphics file format in the Windows operating system. Vector graphics are computer images that are stored in memory as lines rather than a series of dots, so that they can be rotated or scaled proportionally. A Windows metafile is a collection of records that usually, but not always, stores an image or picture. The records contain instructions for a particular graphics device interface which, when executed, reproduce the stored image.
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File Extensions
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A Windows metafile can hold vector information, bitmap information -- a series of bits that represents a graphic image -- and text. The original 16-bit Windows metafile format uses the WMF file extension, while the later 32-bit version, which supports more sophisticated graphics functions, uses the EMF file extension. In either case, the format is optimized to reproduce, or render images very quickly under Windows.
Header Record
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Each Windows metafile starts with a header record, which contains information that defines the characteristics of the metafile. This information includes the type, version and size of the metafile, the number of objects defined within it and the size of the largest single record. The smallest possible Windows metafile contains a header record, but no other records, and occupies 18 bytes of memory.
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Other Records
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The remainder of a Windows metafile typically consists of a series of records representing drawing commands, object definitions and configuration settings. Windows metafile records can be grouped in several general categories, including bitmap record types, which manage and output bitmaps, control record types, which define the start and end of the metafile, and object record types, which create and manage graphics objects. The last record in a Windows metafile should be an end-of-file record, with a length of three words and a function number of zero. If the last record is not an end-of-file record, Windows parses the file for the record.
Characteristics
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Each Windows metafile record has a generic format and includes the record size, record function and any parameters required by the record function. The precise characteristics of a Windows metafile are determined by the application that writes or reads the metafile. Graphics objects, for example, may be defined in metafile records prior to the records in which they are used, so they are reusable. In any case, the structure of a metafile allows its contents to be stored in memory, rendered on a display or printed on a printer or plotter.
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References
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