SHX fonts

AutoCAD font and shape files (SHX) are compiled from shape definition files (SHP). You can create or modify shape definition files with a text editor or word processor that saves files in ASCII format.

The syntax of the shape description for each shape or character is the same regardless of the final use (shape or font) for that shape description. If a shape definition file is to be used as a font file, the first entry in the file describes the font itself rather than a shape within the file. If this initial entry describes a shape, the file is used as a shape file.

Shape Descriptions

Being able to create your own shape definitions is a valuable skill. Keep in mind, however, that this is a very complex subject to learn and requires patience.

Each line in a shape definition file can contain up to 128 characters. Longer lines cannot be compiled. Because AutoCAD ignores blank lines and text to the right of a semicolon, you can embed comments in shape definition files.

Each shape description has a header line of the following form and is followed by one or more lines containing specification bytes, separated by commas and terminated by a 0.

"*shapenumber,defbytes,shapename"
"specbyte1,specbyte2,specbyte3,...,0"

The following list describes the fields of a shape description:

hapenumber

A number, unique to the file, between 1 and 258 (and up to 32768 for Unicode fonts), and preceded by an asterisk (*). Non-Unicode font files use the shape numbers 256, 257, and 258 for the symbolic identifiers Degree_Sign, Plus_Or_Minus_Sign, and Diameter_Symbol. For Unicode fonts these glyphs appear at the U+00B0, U+00B1, and U+2205 shape numbers and are part of the “Latin Extended-A” subset.

Text fonts (files containing shape definitions for each character) require specific numbers corresponding to the value of each character in the ASCII code; other shapes can be assigned any numbers.

defbytes

The number of data bytes (specbytes) required to describe the shape, including the terminating 0. The limit is 2,000 bytes per shape.

hapename

The shape name. Shape names must be uppercase to be recognized. Names with lowercase characters are ignored and are usually used to label font shape definitions.

pecbyte

A shape specification byte. Each specification byte is a code that defines either a vector length and direction or one of a number of special codes. A specification byte can be expressed in the shape definition file as either a decimal or hexadecimal value. This section uses both decimal and hexadecimal specification byte values for its examples (as do many of the shape definition files). If the first character of a specification byte is a 0 (zero), the two characters that follow are interpreted as hexadecimal values.

Vector Length and Direction Code

A simple shape specification byte contains vector length and direction encoded into one specification byte.

A simple shape specification byte contains vector length and direction encoded into one specification byte (one specbyte field). Each vector length and direction code is a string of three characters. The first character must be a 0, which indicates to AutoCAD that the next two characters are interpreted as hexadecimal values. The second character specifies the length of the vector in units. Valid hexadecimal values range from 1 (one unit long) through F (15 units long). The third character specifies the direction of the vector. The following figure illustrates the direction codes.

All the vectors in the preceding figure were drawn with the same length specification. Diagonal vectors stretch to match the X or Y displacement of the closest orthogonal vector. This is similar to the action of the snap grid in AutoCAD.

The following example constructs a shape named DBOX with an arbitrarily assigned shape number of 230.

"*230,6,DBOX"
"014,010,01C,018,012,0"

The preceding sequence of specification bytes defines a box one unit high byone unit wide, with a diagonal line running from the lower left to the upper right. After saving the file as dbox.shp, use the COMPILE command to generate the dbox.shx file. Use the LOAD command to load the shape file containing this definition, and then use the SHAPE command as follows:

Command: shape

Enter shape name or [?] : dbox

Specify insertion point: 1,1

Specify height : 2

Specify rotation angle : 0

The resulting shape is shown in the following illustration.

Operation Codes

In addition to defining vectors, a specification byte can use special codes to create additional forms and specify certain actions, they are called Operation Codes.

To use an operation code, the second character of the three-character string (the vector length specification) must be 0, or you can specify only the code number. For example, 008 and 8 are both valid specifications.

Codes 0, 1, and 2: End of Shape and Draw Mode Control

Code 0 marks the end of the shape definition.

Codes 1 and 2 control Draw mode. Draw is activated at the start of each shape. When Draw mode is turned on (code 1), the vectors cause lines to be drawn. When Draw mode is turned off (code 2), the vectors move to a new location without drawing.

Codes 3 and 4: Size Control

Codes 3 and 4 control the relative size of each vector. The height specified with the SHAPE command is initially considered the length of a single orthogonal vector (direction 0, 4, 8, or C). Code 3 divides vector lengths by the next byte. Code 4 multiplies vector lengths by the next byte. Codes 3 and 4 are followed by a specification byte containing an integer scale factor (1 through 255). If you want the shape height to specify the size of the entire shape, and you use 10 vector lengths to draw it, you can use 3,10 to scale the height specification. The scale factor is cumulative within a shape; that is, multiplying by 2 and again by 6 results in a scale factor of 12. Usually, you should reverse the effect of your scale factors at the end of the shape, especially for subshapes and text font shapes. AutoCAD does not reset the scale factor for you.

Codes 5 and 6: Location Save/Restore

Code 5 pushes (saves) and code 6 pops (restores) the current coordinate position while drawing a shape so that you can return to it from a later point in the shape. You must pop everything you push. The position stack is only four locations deep. If the stack overflows because of too many pushes or too many missing pops, the following message is displayed when the shape is drawn.

:"Position stack overflow in shape nnn"

Similarly, if you try to pop more locations than have been pushed onto the stack, the following message is displayed when the shape is drawn.

:"Position stack underflow in shape nnn"

Code 7: Subshape

Code 7 draws the subshape number given by the next byte. For a non-Unicode font the specification byte following code 7 is a shape number from 1 to 255. For a Unicode font, code 7 is followed by a Unicode shape number from 1 to 65535. Unicode shape numbers should be counted as two bytes (for specific information about the differences between Unicode and non-Unicode fonts). The shape with that number (in the same shape file) is drawn at this time. Draw mode is not reset for the new shape. When the subshape is complete, drawing the current shape resumes.

Codes 8 and 9: X-Y Displacements

Normal vector specification bytes draw only in the 16 predefined directions, and the longest length is 15. These restrictions help make shape definitions efficient but are sometimes limiting. With codes 8 and 9 you can draw nonstandard vectors using X-Y displacements. Code 8 specifies the X-Y displacement given by the next two bytes. Code 8 must be followed by two specification bytes in the format:

:"8,X-displacement,Y-displacement"

The X-Y displacements can range from -128 to +127. A leading + is optional, and you can use parentheses to improve readability. The following example results in a vector that draws (or moves) 10 units to the left and three units up.

:"8,(-10,3)"

Following the two displacement specification bytes, the shape returns to Normal Vector mode.

You can use code 9 to draw a sequence of nonstandard vectors. Code 9 specifies any number of X-Y displacement pairs. The code sequence is terminated by a (0,0) pair. The following example draws three nonstandard vectors and returns to Normal Vector mode.

:"9,(3,1),(3,2),(2,-3),(0,0)"

You must terminate the sequence of X-Y displacement pairs with a (0,0) pair in order for AutoCAD to recognize any Normal Vectors or special codes that follow.

Code 00A: Octant Arc

Special code 00A (or 10) uses the next two specification bytes to define an arc. This is called an octant arc because it spans one or more 45-degree octants, starting and ending on an octant boundary. Octants are numbered counterclockwise from the 3 o'clock position, as shown in the following illustration.

The arc specification is

:"10,radius,(-)0SC"

The radius can be any value from 1 through 255. The second specification byte indicates the direction of the arc (counterclockwise if positive, and clockwise if negative), its starting octant (s, a value from 0 through 7), and the number of octants it spans (c, a value from 0 through 7, in which 0 equals eight octants, or a full circle). You can use parentheses to improve readability. For example, consider the following fragment of a shape definition:

:"...012,10,(1,-032),01E,..."

This code draws a one-unit vector up and to the right, a clockwise arc from octant 3 (with a radius of one unit for two octants), and then a one-unit vector down and to the right, as shown in the following illustration.

Code 00B: Fractional Arc

Special code 00B (11) draws an arc that doesn't necessarily start and end on an octant boundary. The definition uses five specification bytes.

:"11,start_offset,end_offset,high_radius,radius,(-)0SC"

The "start_offset" and "end_offset" represent how far from an octant boundary the arc begins or ends. The "high_radius" represents the most significant eight bits of the radius; the high radius will be 0 unless the radius is greater than 255 units. Multiply the "high_radius" value by 256 and add that value to the radius value to generate an arc radius greater than 255. The "radius" and ending specification byte are the same as for the octant arc specification (code 00A, described previously).

You determine the "startoffset" by calculating the difference in degrees between the starting octant's boundary (a multiple of 45 degrees) and the start of the arc. Then, you multiply this difference by 256 and divide by 45. If the arc starts on an octant boundary, its "start offset" is 0.

The "end offset" is calculated in a similar fashion, but you use the number of degrees from the last octant boundary crossed to the end of the arc. If the arc ends on an octant boundary, its "end offset" is 0.

For example, a fractional arc from 55 degrees to 95 degrees with a 3 unit radius would be coded as follows:

:"11,(56,28,0,3,012)"

Here is the explanation:

:"start_offset = 56 because ((55 - 45) * 256 / 45) = 56"
:"end_offset = 28 because ((95 - 90) * 256 / 45) = 28"
:"high_radius = 0 because (radius < 255)"
:"radius = 3 "
:"starting octant = 1 because"
:"arc starts in the 45 degree octant"
:"ending octant = 2 because"
:"arc ends in the 90 degree octant"

Codes 00C and 00D: Bulge-Specified Arcs

Special codes 00C and 00D (12 and 13) provide another mechanism for including arc segments in shape descriptions. They are similar to codes 8 and 9 in that you can use them to specify X-Y displacements. However, codes 00C and 00D draw arcs by applying a bulge factor to the displacement vector. Code 00C draws one arc segment, while code 00D draws multiple arc segments (polyarcs) until it is terminated by a (0,0) displacement.

Code 00C must be followed by three bytes describing the arc:

:"0C,X-displacement,Y-displacement,Bulge"

Both the X and Y displacement and the bulge, which specifies the curvature of the arc, can range from -127 to +127. If the line segment specified by the displacement has length D, and the perpendicular distance from the midpoint of that segment has height H, the magnitude of the bulge is ((2* H / D) * 127). The sign is negative if the arc from the current location to the new location is clockwise.

A semicircle has bulge 127 (or -127) and is the greatest arc that can be represented as a single-arc segment using these codes (use two consecutive arc segments for larger arcs). A bulge specification of 0 is valid and represents a straight-line segment. Note, however, that using code 8 for a straight-line segment saves a byte in the shape description.

The polyarc code (00D, or 13) is followed by 0 or by more arc segment triples, and is terminated by a (0,0) displacement. Note that no bulge is specified after the final displacement. For example, the letter S might be defined by the following sequence:

:"13,(0,5,127),(0,5,-127),(0,0)"

Zero bulge segments are useful within polyarcs to represent straight segments; they are more efficient than terminating the polyarc, inserting one straight segment, and then starting another polyarc.

The number -128 cannot be used in arc segment and polyarc definitions.

Code 00E: Flag Vertical Text Command

Special code 00E (14) is used only in dual-orientation text font descriptions, where the font is used in both horizontal and vertical orientations. When this special code is encountered in a character definition, the next code is either processed or skipped, depending on orientation. If the orientation is vertical, the next code is processed; if it is horizontal, the next code is skipped.

In horizontal text, the start point for each character is the left end of the baseline. In vertical text, the start point is assumed to be the top center of the character. At the end of each character, a pen-up segment is normally drawn to position to the next character's start point. For horizontal text, it is to the right; for vertical text, it is downward. The special 00E (14) code is used primarily to adjust for differences in start points and endpoints, permitting the same character shape definition to be used both horizontally and vertically. For instance, the following definition of an uppercase D could be used in either horizontal or vertical text.

:"*68,22,ucd"
:"2,14,8,(-2, -6),1,030,012,044,016,038,2,010,1,06C,2,050,"
:"14,8,(-4,-3),0"

Text Font Descriptions

Text fonts must include a special shape number 0 that conveys information about the font itself.

AutoCAD is packaged with numerous text fonts. You can use the STYLE command to apply expansion, compression, or obliquing to any of these fonts, thereby tailoring the characters to your needs. You can draw text of any height, at any baseline angle, and with either horizontal or vertical orientation using these fonts.

AutoCAD text fonts are files of shape definitions with shape numbers corresponding to the ASCII code for each character. Codes 1 through 31 are for control characters, only one of which is used in AutoCAD text fonts:

10 (LF)
The line feed (LF) must drop down one line without drawing. This is used for repeated TEXT commands, to place succeeding lines below the first one.
:"*10,5,lf":"2,8,(0,-10),0"You can modify the spacing of lines by adjusting the downward movement specified by the LF shape definition.

Text fonts must include a special shape number 0 that conveys information about the font itself. The format has the following syntax:

:"*0,4,font-name"
:"above,below,modes,0"

The "above" value specifies the number of vector lengths above the baseline that the uppercase letters extend, and "below" indicates how far the lowercase letters descend below the baseline. The baseline is similar in concept to the lines on writing paper. These values define the basic character size and are used as scale factors for the height specified in the TEXT command.

The "modes" byte should be 0 for a horizontally oriented font and 2 for a dual-orientation (horizontal or vertical) font. The special 00E (14) command code is honored only when "modes" is set to 2.

The standard fonts supplied with AutoCAD include a few additional characters required for the AutoCAD dimensioning feature.:%%d Degree symbol (°):%%p Plus/minus tolerance symbol (±):%%c Circle diameter dimensioning symbolYou can use these and the %%nnn control sequences, as described under TEXT in the Command Reference.

NoteAutoCAD draws text characters by their ASCII codes (shape numbers) and not by name. To save memory, specify the shape name portion of each text shape definition in lowercase as shown in the following example. (Lowercase names are not saved in memory.)

:"*65,11,uca"
:"024,043,04d,02c,2,047,1,040,2,02e,0"

Because the shape name uca contains lowercase letters, AutoCAD doesn't save the name in memory. However, you can use the name for reference when editing the font definition file. In this example, uca stands for uppercase A.

Big Font Descriptions

Some languages, such as Japanese, use text fonts with thousands of non-ASCII characters. In order for drawings to contain such text, AutoCAD supports a special form of shape definition file called a "Big Font file".

Define a Big Font

Special codes in the first line of a Big Font file specify how to read two-byte hexidecimal codes.

A font with hundreds or thousands of characters must be handled differently from a font containing the ASCII set of up to 256 characters. In addition to using more complicated techniques for searching the file, AutoCAD needs a way to represent characters with two-byte codes as well as one-byte codes. Both situations are addressed by the use of special codes at the beginning of a Big Font file.

The first line of a Big Font shape definition file must be as follows:

:"*BIGFONT nchars,nranges,b1,e1,b2,e2,..."

where "nchars" is the approximate number of character definitions in this set; if it is off by more than about 10 percent, either speed or file size suffers. You can use the rest of the line to name special character codes (escape codes) that signify the start of a two-byte code. For example, on Japanese computers, Kanji characters start with hexadecimal codes in the range 90-AF or E0-FF. When the operating system sees one of these codes, it reads the next byte and combines the two bytes into a code for one Kanji character. In the *BIGFONT line, "nranges" tells how many contiguous ranges of numbers are used as escape codes; "b1, e1, b2, e2," and so on, define the beginning and ending codes in each range. Therefore, the header for a Japanese Big Font file might look like this:

:"*BIGFONT 4000,2,090,0AF,0E0,0FF"

After the *BIGFONT line, the font definition is just like a regular AutoCAD text font, except that character codes (shape numbers) can have values up to 65535.

Define an Extended Big Font File

To reduce the size of composite Kanji characters, you can define an extended Big Font file. Extended big fonts use the subshape code, followed immediately by a 0.

The first line of an extended Big Font file is the same as the regular Big Font file. This is the format for the remaining lines of the file:

:"*0,5,font-name"
:"character-height, 0, modes, character-width,0"
:"."
:"."
:"."
:"*shape-number,defbytes,shape-name"
:"."
:"code,0,primitive#,basepoint-x,basepoint-y,width,height,"
:"."
:"."
:"code,0,primitive#,basepoint-x,basepoint-y,width,height,"
:"."
:"terminator"

The following list describes the fields of a Big Font definition file:

character height
Used along with character width to indicate the number of units that define the font characters.

character width
Used along with character height to indicate the number of units that define the font characters. The character-height and character-width values are used to scale the primitives of the font. In this context, primitives are the points, lines, polygons, or character strings of the font geometrically oriented in two-dimensional space. A Kanji character consists of several primitives used repeatedly in different scales and combinations.

modes
The modes byte should be 0 for a horizontally oriented font and 2 for a dual-orientation (horizontal or vertical) font. The special 00E (14) command code is honored only when modes is set to 2.

shape-number
Character code.

defbytes
Byte size. It is always 2 bytes, consisting of a hexadecimal or a combination of decimal and hexadecimal codes.

shape-name
Character name.

code
Shape description special code. It is always 7 so that it can use the subshape feature.

primitive#
Reference to the subshape number. It is always 2.

basepoint-x
X origin of the primitive.

basepoint-y
Y origin of the primitive.

width
Scale of the width of the primitive.

height
Scale of the height of the primitive.

terminator
End-of-file indicator for the shape definition. It is always 0.

To arrive at the scale factor, AutoCAD scales down the primitive to a square unit and then multiplies it by the height and width to get the shape of the character. Character codes (shape numbers) in the Big Font shape definition file can have values up to 65535. The following table describes the fields of the extended Big Font file.

The following figure is an example of a 16 x 16 dot matrix that you could use to design an extended Big Font, such as a Kanji character. In the example, the distance between each dot is one unit. The callout points to a square unit.
The following figure shows examples of Kanji characters. Each character occupies an M×N matrix (matrices don't have to be square), similar to the one shown in the previous figure. The numbers above each figure are the associated shape numbers.

The following figure shows Kanji primitives.
Note Not all fonts are defined in a square matrix; some are defined in rectangular matrices.

Use Big Font Text in a Drawing

To use a Big Font for drawing text, you must set up a text style by using the STYLE command and then specify the name of the Big Font file. The same text style can use a normal ASCII font as well; enter only the two file names, separated by a comma. The following example uses the command prompt version of the STYLE command. To enable Big Fonts from the Text Style dialog box, choose the Use Big Font option.

:"Command: -style"
:"Enter name of text style or [?] : style_name"
:"Specify full font name or font file name (TTF or SHX): txt,greek "

AutoCAD assumes that the first name is the normal font and that the second is the big font.If you enter only one name, AutoCAD assumes it is the normal font and removes any associated Big Font.
When you use the STYLE command to list styles or to revise an existing style, AutoCAD displays the normal font file, a comma, and the Big Font file. If the style has only a Big Font file, it is displayed with a leading comma: ,greek.

For each character in a text string, AutoCAD searches the Big Font file first. If the character is not found there, the normal font file is searched.

=Unicode Font Descriptions=