Superscripts and Subscripts in SHX Files

You can modify shape definition files to improve their ability to display superscripts and subscripts.

The AutoCAD SHX fonts have limited superscript and subscript capabilities. However, it is relatively easy to modify shape definition files to improve superscript and subscript capability.

Creating superscripts and subscripts requires two steps. First, the “imaginary pen” that is creating the text, vector by vector, on your screen needs to be shifted up or down. Then, the font “scale” needs to be reduced. In addition, the reverse process has to take place to return to the normal font. The font needs to recognize four new keys: two for superscripts and two for subscripts. To avoid altering the existing font definitions, you can access these with the numeric keypad on your keyboard.

To add superscript and subscript definitions to a font

This example procedure is based on the AutoCAD Romans font file, although a similar method applies to any AutoCAD font. This procedure adds four new shape definitions to a font: super_on, super_off, sub_on, and sub_off, which control the position and size of the characters that follow. For simplicity, this example replaces the left- and right-bracket characters ([and]) and the left and right curly brace characters ({and}) with the new characters. You may choose to replace other characters or use a shape number in the extended range (ASCII codes 128 through 256). If you use an extended shape number, you need to use the %%nnn method (where nnn is the ASCII value of the character) for placing the new characters.

Edit your SHP file with an ASCII text editor.
Search for the shape definitions of the characters you are replacing. To comment out those definitions so the new definitions can take their place, insert a semicolon in front of each line of the shape definition. The shape definition may continue for a number of lines.
The left- and right-bracket characters have ASCII values of 91 and 93 (05B and 05D hex values, if the font is Unicode). The left and right curly brace characters have ASCII values of 123 and 125 (07B and 07D hex).
Add the first and second values on the second line of the definition, and divide the total by 2 as shown in the following example:
```
*UNIFONT,6,Extended Simplex Roman for UNICODE
```
```
21,7,2,0 21 + 7 = 28, then 28 / 2 = 14. This number is used later.
```
Add the following lines to the end of the SHP file:
```
*91,8,super_on 
```
```
2,8,(0,14),003,2,1,0 
```
```
*93,8,super_off 
```
```
2,004,2,8,(0,-14),1,0 
```
```
*123,8,sub_on 
```
```
2,8,(0,-14),003,2,1,0 
```
```
*125,8,sub_off 
```
```
2,004,2,8,(0,14),1,0 
```
Notice the 14 and -14 values in the preceding lines. They are Y axis offsets for the imaginary pen. The value 14 is half the maximum height of a character in this font, which is the correct approximation for superscripts and subscripts. This value needs to be calculated for each font file, but you can modify it any way you want.
Save the file.
Use the COMPILE command to compile the SHP file.
Once the shape is compiled and an appropriate style is defined, you can access the new pen-up and pen-down commands by entering the [, ], {, and } characters. The [ character initiates superscript and the ] character returns from superscript to normal. The { character initiates subscript and the } character returns from subscript to normal.