Computer Graphics Metafiles

GDDM V3R2 Base Application Programming Reference

Computer Graphics Metafiles

GDDM V3R2 Base Application Programming Reference
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A computer graphics metafile (CGM) is a file that contains information about the content of a picture, and conforms to the International Standard, ISO 8632, 1987(E), or later, or is of a similar format.

CGM files can be output to a number of devices, such as plotters. They can also be modified by any of the editors that accept such files.

Note: CGM support is only available in the CMS, TSO, and MVS/Batch environments.

GDDM allows you to save (export) pictures in CGM format, and to load (import) CGM files into GDDM storage. You can also convert CGM files to ADMGDF format, so that CGM files can be modified or processed by GDDM applications, and you can convert ADMGDF files to CGM.

CGM is a fairly broad standard and, as a consequence, applications that generate CGM files do so in their own way. The CGM conversion functions of GDDM are sufficiently general to handle CGM files produced by various graphical applications. Table 25 shows the conversion profiles supplied with GDDM to aid conversion between the ADMGDF format and the CGM format produced by each of the listed graphics applications:


Table 25. GDDM-supplied conversion profiles for conversion of data between ADMGDF and CGM formats.
Conversion profile	Graphics application
ADM	General Purpose
ADMCD	Corel Draw
ADMFP2	Freelance Plus V2
ADMFP3	Freelance Plus V3
ADMHG	Harvard Graphics
ADMMD	Micrografx Designer
Note: In GDDM Version 2 Release 3, the names of these conversion profiles began with the characters CGM. If you specify a profile beginning with CGM, but GDDM cannot find it, GDDM looks for the corresponding profile beginning with ADM.

The parts of the conversion process that are specific to applications are defined in a CGM Conversion Profile. GDDM supplies a profile tailored to each of the applications listed above, although, depending on usage, further tailoring may be necessary.

In a number of instances, the general-purpose profile will produce acceptable output without further tailoring (especially with enhancements added for GDDM V3.2). You may want to use this profile as the basis for your own tailored conversion profiles for applications used by your enterprise. You may need to write your own profiles for other applications. See "Conversion profiles" in topic 13.6 and the information on retrieving pictures for CGM in the GDDM Base Application Programming Guide for more detail.

When GDDM converts files between CGM and ADMGDF formats, an exact correspondence of the picture is not always possible, because the two formats do not map exactly onto each other. Within the limitations described later, GDDM makes the pictures correspond as closely as possible. However, converted pictures are not guaranteed to be identical to the original. The way in which specific orders are handled is described in "GDF order processing (CGSAVE call)" in topic 13.7 and "CGM order processing (CGLOAD call)" in topic 13.8. Note the following general restrictions on the conversions:

GDDM supports only the Binary Encoding as defined in ISO 8632-3.
Some CGM Version 1 orders (such as cell arrays) and all Version 2 and 3 orders are ignored on input. See Table 36 in topic 13.8.
CALS (the US-MIL-D standard) restricts fonts to the Hershey range and certain other fonts. The Hershey fonts are not provided as GDDM fonts, and so, on conversion from CGM to GDF, available GDDM symbol sets are substituted for them. For further details of CALS, see MIL-D-28003A, November 1991 (Federal Information Processing Standard publication 128).
CALS additional pattern sets are not supported on input or output. Some additional linetypes (such as 6, single arrow) are not correctly converted on input.
Double-byte character strings (DBCS) are not supported.
There is no specific support for APL or Katakana characters.

The conversion functions are provided by two GDDM base calls, CGLOAD and CGSAVE. The PL/I declarations for the API calls are in ADMUPINK and ADMUPIRK.

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