1.3.1 Metafile Structure
An EMF metafile begins with a EMR_HEADER record (section 220.127.116.11), which includes the metafile version, its size, the resolution of the device on which the picture was created, and it ends with an EMR_EOF record (section 18.104.22.168). Between them are records that specify the rendering of the image.
The following diagram depicts the structures of different versions of EMF metafiles, which are:
Original: The original version of EMF defined a file container for the device-independent specification of images.<1>
Extension 1: The second version and first extension added a pixel format record and support for OpenGL commands, enhancing the device independence and flexibility of EMF.
Extension 2: The third version and second extension added the capability to measure distances on device surfaces by using the Metric system, enhancing the accuracy and scalability of EMF.
Figure 1: EMF metafile versions
EMF metafiles can be considered to have three parts:
EMF header: An EMR_HEADER record (section 22.214.171.124), possibly with extensions. It contains information concerning the structure and contents of the metafile, including an optional description string and pixel format descriptor.
EMF records: A sequence of drawing orders, property settings, and object definitions (section 2.3). At least one record is present, not counting the header and end-of-file.
EMF end-of-file: The EMR_EOF record (section 126.96.36.199), which is the last record in the EMF metafile.
EMF records are contiguous because the information that is available for traversing the metafile from record to record depends on it. From any given EMF record, except EMR_EOF, the length of that record can be used to move to the next record in the metafile.