1.3.1 Metafile Structure
WMF specifies structures for defining a graphical image. A WMF metafile contains drawing commands, property definitions, and graphics objects in a series of WMF records. In effect, a WMF metafile is a digital recording of an image, and the recording can be played back to reproduce that image. Because WMF metafiles are application-independent, they can be shared among applications and used for image storage.
Original WMF metafiles were device-specific; that is, the graphical images they contained would only be rendered correctly if played back on the output device for which they were recorded. To overcome this limitation, "placeable" WMF metafiles were developed, which contain an extension to the standard header with information about the placement and scaling of the image.
The following figure illustrates the high-level structures of the original and placeable forms of WMF metafile.
Figure 1: Structures of original and placeable Windows metafiles
The META_HEADER Record (section 220.127.116.11) contains information that defines the characteristics of the metafile, including:
The type of the metafile
The version of the metafile
The size of the metafile
The number of objects defined in the metafile
The size of the largest single record in the metafile
The META_PLACEABLE Record (section 18.104.22.168) contains extended information concerning the image, including:
A bounding rectangle
Logical unit size, for scaling
A checksum, for validation
WMF records have a generic format, which is specified in section 2.3. Every WMF record contains the following information:
The record size
The record function
Parameters, if any, for the record function
All WMF metafiles are terminated by a META_EOF Record (section 22.214.171.124).