term% cat index.txt GVIEW(1) General Commands Manual GVIEW(1)
NAME
gview - interactive graph viewer
SYNOPSIS
gview [ -mp ] [ -l logfile ] [ files ]
DESCRIPTION
Gview reads polygonal lines or a polygonal line drawing from an ASCII
input file (which defaults to standard input), and views it interac‐
tively, with commands to zoom in and out, perform simple editing opera‐
tions, and display information about points and polylines. (Multiple
input files are allowed if you want to overlay several line drawings.)
The editing commands can change the color and thickness of the poly‐
lines, delete (or undelete) some of them, and optionally rotate and
move them. It is also possible to generate an output file that re‐
flects these changes and is in the same format as the input.
Since the move and rotate commands are undesirable when just viewing a
graph, they are only enabled if gview is invoked with the -m option.
The -p option plots only the vertices of the polygons.
Clicking on a polyline with button 1 displays the coordinates and a t
value that tells how far along the polyline. (t=0 at the first vertex,
t=1 at the first vertex, t=1.5 halfway between the second and third
vertices, etc.) The -l option generates a log file that lists all
points selected in this manner.
The most important interactive operations are to zoom in by sweeping
out a rectangle, or to zoom out so that everything currently being dis‐
played shrinks to fit in the swept-out rectangle. Other options on the
button 3 menu are unzoom which restores the coordinate system to the
default state where everything fits on the screen, recenter which takes
a point and makes it the center of the window, and square up which
makes the horizontal and vertical scale factors equal.
To take a graph of a function where some part is almost linear and see
how it deviates from a straight line, select two points on this part of
the graph (i.e., select one with button 1 and then select the other)
and then use the slant command on the button 3 menu. This slants the
coordinate system so that the line between the two selected points ap‐
pears horizontal (but vertical still means positive y). Then the zoom
in command can be used to accentuate deviations from horizontal. There
is also an unslant command that undoes all of this and goes back to an
unslanted coordinate system.
There is a recolor command on button 3 that lets you select a color and
change everything to have that color, and a similar command on button 2
that only affects the selected polyline. If the input file uses the
Multi(...) feature explained below, either flavor of recolor allows
you to type a digit in lieu of selecting a color.
The thick or thin command on button 2 changes the thickness of the se‐
lected polyline and there is also an undo command for such edits. Fi‐
nally, button 3 has commands to read a new input file and display it on
top of everything else, restack the drawing order (in case lines of
different color are drawn on top of each other), write everything into
an output file, or exit the program.
Each polyline in an input or output file is a space-delimited x y coor‐
dinate pair on a line by itself, and the polyline is a sequence of such
vertices followed by a label. The label could be just a blank line or
it could be a string in double quotes, or virtually any text that does
not contain spaces and is on a line by itself. The label at the end of
the last polyline is optional. It is not legal to have two consecu‐
tive labels, since that would denote a zero-vertex polyline and each
polyline must have at least one vertex. (One-vertex polylines are use‐
ful for scatter plots.) Under the -l option, a newline causes the se‐
lected polyline's label to appear in the log file (where it could be
seen by invoking tail -f in another window).
If the label after a polyline contains the word Thick or a color name
(Red, Pink, Dkred, Orange, Yellow, Dkyellow, Green, Dkgreen, Cyan,
Blue, Ltblue, Magenta, Violet, Gray, Black, White), whichever color
name comes first will be used to color the polyline. Alternatively,
labels can contain Multi followed by single-letter versions of these
names: (R, P, r, O, Y, y, G, g, C, B, b, M, V, A, K, W, each optionally
preceded by T). Then recolor followed by a nonzero digit n selects the
nth alternative for each polyline.
EXAMPLE
To see a graph of the function y=sin(x)/x, generate input with an awk
script and pipe it into gview:
awk 'BEGIN{for(x=.1;x<500;x+=.1)print x,sin(x)/x}' | gview
SOURCE
/sys/src/cmd/gview.c
SEE ALSO
awk(1), tail(1)
BUGS
The user interface for the slant command is counter-intuitive. Perhaps
it would be better to have a scheme for sweeping out a parallelogram.
The -p option makes the interactive point selection feature behave
strangely, and is unnecessary since extra blank lines in the input
achieve essentially the same effect.
GVIEW(1)