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.TH GVIEW 1

.SH NAME

gview \- interactive graph viewer

.SH SYNOPSIS

.B gview

[

.B -mp

]

[

.B -l

.I logfile

]

[

.I files

]

.SH DESCRIPTION

.I Gview

reads polygonal lines or a polygonal line drawing from an

.B ASCII

input file (which defaults to standard input), and views it interactively,

with commands to zoom in and out, perform simple editing operations, 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 polylines, delete (or undelete)

some of them, and optionally rotate and move them.  It is also possible to

generate an output file that reflects these changes and is in the same format

as the input.

.PP

Since the

.B move

and

.B rotate

commands are undesirable when just viewing a graph, they are only enabled if

.I gview

is invoked with the

.B -m

option.

.PP

The

.B -p

option plots only the vertices of the polygons.

.PP

Clicking on a polyline with button 1 displays the coordinates and a

.I t

value that tells how far along the polyline.

.IR (t =0

at the first vertex,

.IR t =1

at the first vertex,

.IR t =1.5

halfway between the second and third vertices, etc.)  The

.B -l

option generates a log file that lists all points selected in this manner.

.PP

The most important interactive operations are to

.I zoom in

by sweeping out a rectangle, or to

.I zoom out

so that everything currently being displayed shrinks to fit in the swept-out

rectangle.  Other options on the button 3 menu are

.I unzoom

which restores the coordinate system to the default state where everything

fits on the screen,

.I recenter

which takes a point and makes it the center of the window, and

.I square up

which makes the horizontal and vertical scale factors equal.

.PP

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

.I slant

command on the button 3 menu.

This slants the coordinate system so that the line between the two

selected points appears horizontal (but vertical still means positive

.IR y ).

Then the

.I zoom in

command can be used to accentuate deviations from horizontal.

There is also an

.I unslant

command that undoes all of this and goes back to an unslanted coordinate

system.

.PP

There is a

.I 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

.B Multi(...)

feature explained below, either flavor of

.I recolor

allows you to type a digit in lieu of selecting a color.

.PP

The

.I thick

or

.I thin

command on button 2 changes the thickness of the selected polyline

and there is also an undo command for such edits.

Finally, button 3 has commands to

.I read

a new input file and display it on top of everything else,

.I restack

the drawing order (in case lines of different color are drawn on top of

each other),

.I write

everything into an output file, or

.I exit

the program.

.PP

Each polyline in an input or output file is a space-delimited

.I x

.I y

coordinate 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 consecutive labels, since that

would denote a zero-vertex polyline and each polyline must have at least

one vertex. (One-vertex polylines are useful for scatter plots.)

Under the

.B -l

option, a newline causes the selected polyline's label to appear in

the log file (where it could be seen by invoking

.B tail -f

in another window).

If the label after a polyline contains the word

.B "Thick"

or a color name

.BR (Red ,

.BR Pink ,

.BR Dkred ,

.BR Orange ,

.BR Yellow ,

.BR Dkyellow ,

.BR Green ,

.BR Dkgreen ,

.BR Cyan ,

.BR Blue ,

.BR Ltblue ,

.BR Magenta ,

.BR Violet ,

.BR Gray ,

.BR Black ,

.BR White ),

whichever color name comes first will be used to color the polyline.

Alternatively, labels can contain

.B Multi

followed by single-letter versions of these names:

.BR (R ,

.BR P ,

.BR r ,

.BR O ,

.BR Y ,

.BR y ,

.BR G ,

.BR g ,

.BR C ,

.BR B ,

.BR b ,

.BR M ,

.BR V ,

.BR A ,

.BR K ,

.BR W ,

each optionally preceded by

.BR T ).

Then

.I recolor

followed by a nonzero digit

.I n

selects the

.IR n th

alternative for each polyline.

.SH EXAMPLE

To see a graph of the function

.IR y = sin( x )/ x ,

generate input with an awk script and pipe it into

.IR gview :

.IP

.EX

awk 'BEGIN{for(x=.1;x<500;x+=.1)print x,sin(x)/x}' | gview

.EE

.SH SOURCE

.B /sys/src/cmd/gview.c

.SH SEE ALSO

.IR awk (1),

.IR tail (1)

.SH BUGS

The user interface for the

.I slant

command is counter-intuitive.  Perhaps it would be better to have a scheme

for sweeping out a parallelogram.

.PP

The

.B -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.