Also Known As: GEM Vector, VDI, .GDI
| Type | Metafile |
| Colors | 256 |
| Compression | Uncompressed |
| Maximum Image Size | 32Kx32K |
| Multiple Images Per File | No |
| Numerical Format | Big-endian |
| Originator | Digital Research |
| Platform | GEM GUI running under MS-DOS, some Ataris |
| Supporting Applications | GEM Artline, GEM Draw Plus, GEM Scan, others |
| See Also | GEM Raster |
Usage
Illustration, drawing, and desktop publishing applications,
and some data interchange.
Comments
A vector format with good support at one time, associated
with the GEM GUI from Digital Research. If you are thinking of
supporting this format, be prepared to draw Bezier curves. It also
has support for embedded bitmaps.
Vendor specifications are available for this format.
Although often called the GEM Vector format, GEM VDI is actually a metafile format and is closely associated with the functioning of the GEM user interface. The GEM system provides a metafile driver that is accessed from within the GEM programming system through a documented API. Display requests to the driver result in items being written to a metafile buffer in GEM's standard metafile format. Metafile elements thus consist of calls to the GEM display system.
Contents:
File Organization
File Details
For Further Information
Supporting GEM VDI is similar to supporting many other metafile formats. Be prepared to duplicate the functionality of the host system, in this case GEM, or at least a reasonable subset of it, before you're through.
We would like to have more information on this format. Information provided by DISCUS (see "For Further Information" below) indicates that the file consists of a header followed by a stream of standard-format metafile items.
The structure for the GEM VDI header is shown below.
typedef struct _GemVdiHeader
{
WORD Identifier; /* Magic number. Always FFFFh */
WORD LengthOfHeader /* Length of the header in 16-bit WORD */
WORD Version; /* Format version number */
WORD Transform; /* Image origin */
WORD Coords[4]; /* Size and position of image */
WORD PageSize[2]; /* Physical page size */
WORD Bounds[4]; /* Limits of coordinate system */
WORD Flags; /* Bit image opcode flag */
} GEMVDIHEADER;
Identifier is the magic number of GEM VDI image files. This value is always FFFFh.
LengthOfHeader is the size of the header described as the number of 16-bit WORDs it contains. This value is typically 0Fh.
Version is the version number of the file format. This value is calculated using the formula: 100 * major version number + minor version number.
Transform is the NDC/RC transformation mode flag. This value is 00h if the origin of the image is in the lower-left corner of the display ("Normalized Device Coordinates") and 02h if the origin is in the upper-left corner ("Raster Coordinates").
Coords are four WORDs indicating the minimum and maximum coordinate values of data in the file. These values indicate the size of the image and its position on the display and are stored as: minimum X, minimum Y, maximum X, maximum Y.
PageSize is the size of the physical printed page the image will cover in 1/10 of millimeters. This value is 00h if the page size is undefined by the application creating the image.
Bounds are four WORDs that describe the maximum extent of the coordinate system used by the image and defined by the application. These values are stored as: lower-left X, lower-left Y, upper-right X, upper-right Y.
Flags contains the bit image opcode flag. The values for this field are 00h if no bit image is included in the file and 01h if a bit image is included. Bits 2 through 15 in Flags should always be set to 0.
Standard format metafile items consist of control, integer, and vertex parameters. This structure is described below.
Word | Value | Description |
|---|---|---|
0 |
control[0] |
Opcode |
1 |
control[1] |
Vertex count |
2 |
control[3] |
Integer parameter count |
3 |
control[5] |
Sub-opcode or zero |
4 |
ptsin[0-n] |
Input vertex list (if provided) |
... |
|
|
n+4 |
intin[0-m] |
Input integer (if provided) |
... |
|
|
Table GEM VDI-1 shows the correspondence of standard metafile items and their opcodes to the display commands accepted by the GEM display subsystem. Arguments appear to be documented only in the GEM Programmer's Toolkit, but you might be able to recover them through diligent application of trial and error.
Routine | Code | Subcode | Metafile Object |
|---|---|---|---|
v_alpha_text |
05 |
19 |
Output Printer Alpha Text |
v_alpha_text |
0b |
19 |
Output Printer Alpha Text |
v_arc |
0b |
02 |
Arc |
v_bar |
0b |
01 |
Bar |
v_bit_image |
05 |
17 |
Output Bit Image File |
v_bit_image |
0b |
17 |
Output Bit Image File |
v_circle |
0b |
04 |
Circle |
v_clear_disp_list |
05 |
16 |
Clear Display List |
v_clrwk |
03 |
NA |
Clear Workstation |
v_ellarc |
0b |
06 |
Elliptical Arc |
v_ellipse |
0b |
05 |
Ellipse |
v_ellpie |
0b |
07 |
Elliptical Pie Slice |
v_entercur |
05 |
03 |
Enter Alpha Mode |
v_entercur |
0b |
13 |
Enter Alpha Mode |
v_exitcur |
05 |
02 |
Exit Alpha Mode |
v_fillarea |
09 |
NA |
Fill Area |
v_form_adv |
05 |
14 |
Form Advance |
v_form_adv |
0b |
14 |
Form Advance |
v_justified |
0b |
0a |
Justified Graphics Text |
v_line |
06 |
NA |
Polyline |
v_output_window |
05 |
15 |
Output Window |
v_pieslice |
0b |
03 |
Pie |
v_pieslice |
0b |
08 |
Rounded Rectangle |
v_pmarker |
07 |
NA |
Polymarker |
v_qtext |
08 |
NA |
Text |
v_rfbox |
0b |
09 |
Filled Rounded Rectangle |
v_updwk |
04 |
NA |
Update Workstation |
vr_recfl |
73 |
NA |
Fill Rectangle |
vs_color |
0e |
NA |
Set Color Representation |
vsf_clip |
81 |
NA |
Set Clipping Rectangle |
vsf_color |
19 |
NA |
Set Fill Color Index |
vsf_interior |
17 |
NA |
Set Fill Interior Style |
vsf_perimeter |
68 |
NA |
Set Fill Perimeter Visibility |
vsf_style |
18 |
NA |
Set Fill Style Index |
vsf_updat |
70 |
NA |
Set User Fill |
vsl_color |
11 |
NA |
Set Polyline Color Index |
vsl_ends |
6c |
NA |
Set Polyline End Styles |
vsl_type |
0f |
NA |
Set Polyline Type |
vsl_udsty |
71 |
NA |
Set User Line Style |
vsl_width |
10 |
NA |
Set Polyline Width |
vsm_color |
14 |
NA |
Set Polymarker Color Index |
vsm_height |
13 |
NA |
Set Polymarker Height |
vsm_type |
12 |
NA |
Set Polymarker Type |
vst_alignment |
27 |
NA |
Set Graphic Text Alignment |
vst_color |
16 |
NA |
Set Text Color Index |
vst_effects |
6a |
NA |
Set Graphics Text Effects |
vst_font |
15 |
NA |
Set Text Font |
vst_height |
0c |
NA |
Set Character Height |
vst_point |
6b |
NA |
Set Character Height (points) |
vst_rotation |
0d |
NA |
Set Character Baseline Vector |
vswr_mode |
20 |
NA |
Set Writing Mode |
There are also two non-standard metafile items:
| v_opnwk | Open Workstation |
| v_clswk | Close Workstation |
There are three metafile escape functions:
| v_meta_extents | Update Metafile Extents |
| v_write_meta | Write Metafile Item |
| vm_filename | Change GEM VDI Filename |
There are several inquire functions:
| vq_chcells | Inquire Addressable Character Cells |
| vq_color | Inquire Color Representation |
| vq_attributes | Inquire Current Polyline Attributes |
| vq_extnd | Extended Inquire |
Several metafile sub-opcodes are reserved for the Digital Research GEM Output application:
| Physical Page Size |
| Coordinate Window |
Several metafile sub-opcodes are also reserved for the Digital Research GEM Draw Plus application:
| Group |
| Set No Line Style |
| Set Attribute Shadow On |
| Set Attribute Shadow Off |
| Start Draw Area Type Primitive |
| End Draw Area Type Primitive |
Also associated with the GEM VDI format is a standard keyboard mapping.
The GEM VDI format originated at Digital Research, which is now owned by Novell, and GEM VDI is currently being supported by DISCUS Distribution Services, a service organization. Note that DISCUS will provide support only if you have first purchased the GEM Programmer's Toolkit from Digital Research. You can contact DISCUS at:
DISCUS Distribution Services, Inc.
8020 San Miguel Canyon Road
Salinas, CA 93907-1208
Voice: 408-663-6966
You may still be able to get some information from Novell/Digital Research at:
Novell/Digital Research, Inc.
P.O. Box DRI
Monterey, CA 93942
Voice: 408-649-3896
Voice: 800-848-1498
BBS: 408-649-3896
We have also been able to include information on Atari support of GEM VDI on the CD-ROM.
Copyright © 1996, 1994 O'Reilly & Associates, Inc. All Rights Reserved.
