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GVIEW(1)							      GVIEW(1)

       gview - interactive graph viewer

       gview [ -mp ] [ -l logfile ] [ files ]

       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
       reflects 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
       appears	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
       selected	 polyline  and	there  is also an undo command for such edits.
       Finally, 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
       selected 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.

       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


       awk(1), tail(1)

       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.

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