Getting info back from gnuplot for auto range values

[Daniel J Sebald]

John,

Attached is a patch illustrating how to get information back from gnuplot about 
auto axis ranging results if you are still interested.  Rather than remove what 
would be extraneous code, I simply commented out the line of code that would 
use the octave computed settings.  That way, this patch more clearly shows how 
to get the variables of interest.

It would be nice if the communication link could be done through a pipe or stream.  
However, I didn't have much luck with the pipe() command.  First, it would have to be a 
pipe that has a file system name so that gnuplot could use "set print 
'|filename'".  Second, reading from the pipe created with pipe() seems to get stuck 
for me, i.e., put something into the WRITE_FD and try to read from READ_FD just hangs.

Dan

diff -Pur octave-cvs/scripts/plot/__go_draw_axes__.m 
octave-mod/scripts/plot/__go_draw_axes__.m
--- octave-cvs/scripts/plot/__go_draw_axes__.m  2007-06-19 01:00:08.000000000 
-0500
+++ octave-mod/scripts/plot/__go_draw_axes__.m  2007-06-20 01:32:52.285126823 
-0500
@@ -511,7 +511,7 @@
 
     if (xautoscale && have_data)
       xlim = get_axis_limits (xmin, xmax, xminp, xlogscale);
-      set (h, "xlim", xlim, "xlimmode", "auto");
+%      set (h, "xlim", xlim, "xlimmode", "auto");
     else
       xlim = axis_obj.xlim;
     endif
@@ -524,7 +524,7 @@
 
     if (yautoscale && have_data)
       ylim = get_axis_limits (ymin, ymax, yminp, ylogscale);
-      set (h, "ylim", ylim, "ylimmode", "auto");
+%      set (h, "ylim", ylim, "ylimmode", "auto");
     else
       ylim = axis_obj.ylim;
     endif
@@ -538,7 +538,7 @@
     if (nd == 3)
       if (zautoscale && have_data)
        zlim = get_axis_limits (zmin, zmax, zminp, zlogscale);
-       set (h, "zlim", zlim, "zlimmode", "auto");
+%      set (h, "zlim", zlim, "zlimmode", "auto");
       else
        zlim = axis_obj.zlim;
       endif
@@ -637,6 +637,20 @@
 
     fflush (plot_stream);
 
+    % Get information back from gnuplot about axis limits
+    if (xautoscale)
+      xlim = __gnuplot_read_limits__ (plot_stream, "X");
+      set (h, "xlim", xlim, "xlimmode", "auto");
+    endif
+    if (yautoscale)
+      ylim = __gnuplot_read_limits__ (plot_stream, "Y");
+      set (h, "ylim", ylim, "ylimmode", "auto");
+    endif
+    if (nd == 3 && zautoscale)
+      zlim = __gnuplot_read_limits__ (plot_stream, "Z");
+      set (h, "zlim", zlim, "zlimmode", "auto");
+    endif
+
   else
     print_usage ();
   endif    
@@ -896,6 +910,27 @@
 
 endfunction
 
+function lim = __gnuplot_read_limits__ (plot_stream, dim)
+  
+  ## Set gnuplot's print command to a file, print the values of
+  ## interest and then read them.  It would be nice if this
+  ## were a pipe so that continually opening and closing files
+  ## wasn't necessary.
+
+  persistent __gpprintfile__ = "";
+
+  if (isempty (__gpprintfile__))
+    __gpprintfile__ = tmpnam ();
+  endif
+  fprintf (plot_stream, "set print \"-\";\nset print \"%s\";\n", 
__gpprintfile__);
+  fprintf (plot_stream, "print GPVAL_%s_MIN;\nprint GPVAL_%s_MAX;\n", dim, 
dim);
+  fputs (plot_stream, "set print \"-\";\n");
+  gpfid = fopen (__gpprintfile__);
+  lim = fscanf (gpfid, "%g", 2)(:)';
+  fclose (gpfid);
+
+endfunction
+
 function do_tics (obj, plot_stream)
   do_tics_1 (obj.xtickmode, obj.xtick, obj.xticklabelmode, obj.xticklabel,
             "x", plot_stream);