Appendix A -- Drawing Interchange File Formats
Slide Files

NOTE This information is for experienced programmers, and is subject to change without notice.

AutoCAD slide files are screen images written by the MSLIDE command and read by the VSLIDE command. This section describes the format of slide files for the benefit of developers who wish to incorporate support for AutoCAD slides into their programs.

A slide file consists of a header portion (31 bytes) and one or more data records of variable length. All coordinates and sizes written to the slide file reflect the drawing area of the display device from which the slide was created with point (0,0) located at the lower-left corner of the drawing area. For AutoCAD Release 9 and later, the slide file header consists of the following fields:

Slide file header
Field Bytes Description

ID string

17

"AutoCAD Slide" CR LF ^Z NUL

Type indicator

1

Currently set to 56 (decimal)

Level indicator

1

Currently set to 2

High X dot

2

Width of the graphics area: 1, in pixels

High Y dot

2

Height of the graphics area: 1, in pixels

Aspect ratio

4

Drawing area aspect ratio (horizontal size/vertical size in inches), scaled by 10,000,000. This value is always written with the least significant byte first.

Hardware fill

2

Either 0 or 2 (value is unimportant)

Test number

2

A number (1234 hex) used to determine whether all 2-byte values in the slide were written with the high-order byte first (Intel 8086-family CPUs) or the low-order byte first (Motorola 68000-family CPUs)

Data records follow the header. Each data record begins with a 2-byte field whose high-order byte is the record type. The remainder of the record may be composed of 1-byte or 2-byte fields as described in the following table. To determine whether the 2-byte fields are written with the high-order byte first or the low-order byte first, examine the Test number field of the header that is described in the previous table.

Slide file data records
Record type
(hex)

Bytes

Meaning

Description

00-7F

8

Vector

The from-X coordinate for an ordinary vector. From-Y, to-X, and to-Y follow in that order as 2-byte values. The from point is saved as the last point.

80-FA

-

Undefined

Reserved for future use

FB

5

Offset vector

The low-order byte and the following three bytes specify the endpoints (from-X, from-Y, to-X, to-Y) of a vector, in terms of offsets (-128 to +127) from the saved last point. The adjusted from point is saved as the last point for use by subsequent vectors.

FC

2

End of file

The low-order byte is 00.

FD

6

Solid fill

The low-order byte is always zero. The following two 2-byte values specify the X and Y coordinates of one vertex of a polygon to be solid filled. Three to ten such records occur in sequence. A Solid fill record with a negative Y coordinate indicates the start or end of such a flood sequence. In the start record, the X coordinate indicates the number of vertex records to follow.

FE

3

Common
endpoint
vector

This is a vector starting at the last point. The low-order byte and the following byte specify to-X and to-Y in terms of offsets (-128 to +127) from the saved last point. The adjusted to point is saved as the last point for use by subsequent vectors.

FF

2

New color

Subsequent vectors are to be drawn using the color number indicated by the low-order byte.

If a slide contains any vectors at all, a New color record will be the first data record. The order of the vectors in a slide, and the order of the endpoints of those vectors, may vary.

For example, the following is an annotated hex dump of a simple slide file created on an IBM PC/AT with an IBM Enhanced Graphics Adapter. The slide consists of a white diagonal line from the lower-left corner to the upper-right corner of the drawing area, a green vertical line near the lower-left corner, and a small red rectangle at the lower-left corner.

41 75 74 6F 43 41            ID string ("AutoCAD Slide" CR LF ^Z NUL)
44 20 53 6C 69 64
65 0D 0A 1A 00
56                           Type indicator (56)
02                           Level indicator (2)
3C 02                        High X dot (572)
24 01                        High Y dot (292)
0B 80 DF 00                  Aspect ratio (14,647,307 / 10,000,000 = 1.46)
02 00                        Hardware fill (2)
34 12                        Test number (1234 hex)
07 FF                        New color (7 = white)
3C 02 24 01 00 00 00 00      Vector from 572,292 to 0,0. 572,292 becomes "last" point
3 FF                         New color (3 = green)
0F 00 32 00 0F 00 13 00      Vector from 15,50 to 15,19. \x1115,50 becomes "last" point
01 FF                        New color (1 = red)
12 FB E7 12 CE               Offset vector from 15+18,50-25 (33,25) to 15+18,50-
                               50 (33,0). 33,25 becomes "last" point  

DF FE 00                     Common-endpoint vector from 33,25 to 33-33,25+0
                               (0,25). 0,25 becomes "last" point

00 FE E7                     Common-endpoint vector from (0,25) to 0+0,25-25
                               (0,0). 0,0 becomes "last" point

21 FE 00                     Common-endpoint vector from (0,0) to 0+33,0+0
                               (33,0).33,0 becomes "last" point

00 FC                        End of file


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