GPS(4) — Silicon Graphics

NAME

gps − graphical primitive string, format of graphical files

DESCRIPTION

GPS is a format used to store graphical data. Several routines have been developed to edit and display GPS files on various devices. Also, higher level graphics programs such as plot (in stat(1G)) and vtoc (in toc(1G)) produce GPS format output files.

A GPS is composed of five types of graphical data or primitives.

GPS PRIMITIVES

lines The lines primitive has a variable number of points from which zero or more connected line segments are produced. The first point given produces a move to that location. (A move is a relocation of the graphic cursor without drawing.) Successive points produce line segments from the previous point. Parameters are available to set color, weight, and style (see below).

arc The arc primitive has a variable number of points to which a curve is fit. The first point produces a move to that point. If only two points are included a line connecting the points will result, if three points a circular arc through the points is drawn, and if more than three, lines connect the points. (In the future, a spline will be fit to the points if they number greater than three.) Parameters are available to set color, weight, and style.

text The text primitive draws characters. It requires a single point which locates the center of the first character to be drawn. Parameters are color, font, textsize, and textangle.

hardware The hardware primitive draws hardware characters or gives control commands to a hardware device. A single point locates the beginning location of the hardware string.

comment A comment is an integer string that is included in a GPS file but causes nothing to be displayed. All GPS files begin with a comment of zero length.

GPS PARAMETERS

color Color is an integer value set for arc, lines, and text primitives.

weight Weight is an integer value set for arc and lines primitives to indicate line thickness. The value 0 is narrow weight, 1 is bold, and 2 is medium weight.

style Style is an integer value set for lines and arc primitives to give one of the five different line styles that can be drawn on Tektronix 4010 series storage tubes. They are:

0     solid
1     dotted
2     dot dashed
3     dashed
4     long dashed

font An integer value set for text primitives to designate the text font to be used in drawing a character string. (Currently font is expressed as a four-bit weight value followed by a four-bit style value.)

textsize Textsize is an integer value used in text primitives to express the size of the characters to be drawn. Textsize represents the height of characters in absolute universe-units and is stored at one-fifth this value in the size-orientation (so) word (see below).

textangle Textangle is a signed integer value used in text primitives to express rotation of the character string around the beginning point. Textangle is expressed in degrees from the positive x-axis and can be a positive or negative value. It is stored in the size-orientation (so) word as a value 256/360 of its absolute value.

ORGANIZATION

GPS primitives are organized internally as follows:

linescw points sw
arccw points sw
textcw point sw so [string]
hardwarecw point [string]
commentcw [string]

cw Cw is the control word and begins all primitives. It consists of four bits that contain a primitive-type code and twelve bits that contain the word-count for that primitive.

point(s) Point(s) is one or more pairs of integer coordinates. Text and hardware primitives only require a single point. Point(s) are values within a Cartesian plane or universe having 64K (−32K to +32K) points on each axis.

sw Sw is the style-word and is used in lines, arc, and text primitives. The first eight bits contain color information. In arc and lines the last eight bits are divided as four bits weight and four bits style. In the text primitive the last eight bits of sw contain the font.

so So is the size-orientation word used in text primitives. The first eight bits contain text size and the remaining eight bits contain text rotation.

string String is a null-terminated character string. If the string does not end on a word boundary an additional null is added to the GPS file to insure word-boundary alignment.