grn commands

Each input line between .GS and .GE may have one grn command. Commands consist of one or two strings separated by white space, the first string being the command and the second its operand. Commands may be upper- or lowercase and abbreviated down to one character.

Commands that affect a picture's environment (those listed before “default”, see below) are only in effect for the current picture: the environment is reinitialized to the defaults at the start of the next picture. The commands are as follows.

1 N

2 N

3 N

4 N

Set gremlin's text size number 1 (2, 3, or 4) to N points. The default is 12 (16, 24, and 36, respectively).

roman f

italics f

bold f

special f

Set the roman (italics, bold, or special) font to troff's font f (either a name or number). The default is R (I, B, and S, respectively).

l f

stipple f

Set the stipple font to troff's stipple font f (name or number). The command stipple may be abbreviated down as far as “st” (to avoid confusion with “special”). There is no default for stipples (unless one is set by the “default” command), and it is invalid to include a gremlin picture with polygons without specifying a stipple font.

x N

scale N

Magnify the picture (in addition to any default magnification) by N, a floating-point number larger than zero. The command scale may be abbreviated down to “sc”.

narrow N

medium N

thick N

Set the thickness of gremlin's narrow (medium and thick, respectively) lines to N times 0.15pt (this value can be changed at compile time). The default is 1.0 (3.0 and 5.0, respectively), which corresponds to 0.15pt (0.45pt and 0.75pt, respectively). A thickness value of zero selects the smallest available line thickness. Negative values cause the line thickness to be proportional to the current point size.

pointscale [off|on]

Scale text to match the picture. Gremlin text is usually printed in the point size specified with the commands 1, 2, 3, or 4, regardless of any scaling factors in the picture. Setting pointscale will cause the point sizes to scale with the picture (within troff's limitations, of course). An operand of anything but off will turn text scaling on.

default

Reset the picture environment defaults to the settings in the current picture. This is meant to be used as a global parameter setting mechanism at the beginning of the troff input file, but can be used at any time to reset the default settings.

width N

Force the picture to be N inches wide. This overrides any scaling factors present in the same picture. “width 0” is ignored.

height N

Force the picture to be N inches high, overriding other scaling factors. If both width and height are specified, the tighter constraint will determine the scale of the picture. height and width commands are not saved with a “default” command. They will, however, affect point size scaling if that option is set.

file name

Get picture from gremlin file name located the current directory (or in the library directory; see the -M option above). If multiple file commands are given, the last one controls. If name doesn't exist, an error message is reported and processing continues from the .GE line.

Usage with groff

Since grn is a preprocessor, it has no access to elements of formatter state, such as indentation, line length, type size, or register values. Consequently, no troff input can be placed between the .GS and .GE macros. However, gremlin text elements are subsequently processed by troff, so anything valid in a single line of troff input is valid in a line of gremlin text (barring the dot control character “.” at the beginning of a line). Thus, it is possible to have equations within a gremlin figure by including in the gremlin file eqn expressions enclosed by previously defined delimiters (e.g., “$$”).

When using grn along with other preprocessors, it is best to run tbl(1) before grn, pic(1), and/or ideal to avoid overworking tbl. eqn(1) should always be run last. groff(1) will automatically run preprocessors in the correct order.

A picture is considered an entity, but that doesn't stop troff from trying to break it up if it falls off the end of a page. Placing the picture between “keeps” in the me macros will ensure proper placement.

grn uses troff's registers g1 through g9 and sets registers g1 and g2 to the width and height of the gremlin figure (in device units) before entering the .GS macro (this is for those who want to rewrite these macros).

Gremlin file format

There exist two distinct gremlin file formats: the original format for AED graphic terminals, and the Sun or X11 version. An extension used by the Sun/X11 version allowing reference points with negative coordinates is not compatible with the AED version. As long as a gremlin file does not contain negative coordinates, either format will be read correctly by either version of gremlin or grn. The other difference in Sun/X11 format is the use of names for picture objects (e.g., POLYGON, CURVE) instead of numbers. Files representing the same picture are shown below.

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The first line of each gremlin file contains either the string “gremlinfile” (AED) or “sungremlinfile” (Sun/X11).

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The second line of the file contains an orientation and x and y values for a positioning point, separated by spaces. The orientation, either 0 or 1, is ignored by the Sun/X11 version. 0 means that gremlin will display things in horizontal format (a drawing area wider than it is tall, with a menu across the top). 1 means that gremlin will display things in vertical format (a drawing area taller than it is wide, with a menu on the left side). x and y are floating-point values giving a positioning point to be used when this file is read into another file. The stuff on this line really isn't all that important; a value of “1 0.00 0.00” is suggested.

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The rest of the file consists of zero or more element specifications. After the last element specification is a line containing the string “-1”.

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Lines longer than 127 characters are truncated to that length.

Element specifications

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The first line of each element contains a single decimal number giving the type of the element (AED) or its name (Sun/X11).

gremlin File Format: Object Type Specification
AED Number	Sun/X11 Name	Description
0	BOTLEFT	bottom-left-justified text
1	BOTRIGHT	bottom-right-justified text
2	CENTCENT	center-justified text
3	VECTOR	vector
4	ARC	arc
5	CURVE	curve
6	POLYGON	polygon
7	BSPLINE	b-spline
8	BEZIER	Bézier
10	TOPLEFT	top-left-justified text
11	TOPCENT	top-center-justified text
12	TOPRIGHT	top-right-justified text
13	CENTLEFT	left-center-justified text
14	CENTRIGHT	right-center-justified text
15	BOTCENT	bottom-center-justified text

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After the object type comes a variable number of lines, each specifying a point used to display the element. Each line contains an x-coordinate and a y-coordinate in floating-point format, separated by spaces. The list of points is terminated by a line containing the string “-1.0 -1.0” (AED) or a single asterisk, “*” (Sun/X11).

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After the points comes a line containing two decimal values, giving the brush and size for the element. The brush determines the style in which things are drawn. For vectors, arcs, and curves there are six valid brush values.

1	thin dotted lines
2	thin dot-dashed lines
3	thick solid lines
4	thin dashed lines
5	thin solid lines
6	medium solid lines

For polygons, one more value, 0, is valid. It specifies a polygon with an invisible border. For text, the brush selects a font as follows.

1	roman (R font in troff)
2	italics (I font in troff)
3	bold (B font in troff)
4	special (S font in troff)

If you're using grn to run your pictures through groff, the font is really just a starting font. The text string can contain formatting sequences like “\fI” or “\d” which may change the font (as well as do many other things). For text, the size field is a decimal value between 1 and 4. It selects the size of the font in which the text will be drawn. For polygons, this size field is interpreted as a stipple number to fill the polygon with. The number is used to index into a stipple font at print time.

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The last line of each element contains a decimal number and a string of characters, separated by a single space. The number is a count of the number of characters in the string. This information is used only for text elements, and contains the text string. There can be spaces inside the text. For arcs, curves, and vectors, the character count is zero (0), followed by exactly one space before the newline.

Coordinates

gremlin was designed for AED terminals, and its coordinates reflect the AED coordinate space. For vertical pictures, x values range 116 to 511, and y values from 0 to 483. For horizontal pictures, x values range from 0 to 511, and y values from 0 to 367. Although you needn't absolutely stick to this range, you'll get better results if you at least stay in this vicinity. Also, point lists are terminated by a point of (-1, -1), so you shouldn't ever use negative coordinates. gremlin writes out coordinates using the printf(3) format “%f1.2”; it's probably a good idea to use the same format if you want to modify the grn code.

Sun/X11 coordinates

There is no restriction on the range of coordinates used to create objects in the Sun/X11 version of gremlin. However, files with negative coordinates will cause problems if displayed on the AED.