restore pre-5.2 logscale tic increment interpretation

ChangeLog

@@ -1,3 +1,15 @@
+2017-09-23  Ethan A Merritt  <[email protected]>
+
+	* src/axis.c (gen_tics) docs/gnuplot.doc demo/nonlinear6.dem:
+	Revise documentation of "set xtics" to include examples and description
+	of logscale keyword.  Restore pre-5.2 behaviour that for log-scaled axes
+	the increment in "set xtics {start,} incr {,end}" is interpreted as a
+	multiplicative factor rather than a constant interval.  However this is
+	only true if the "logscale" attribute is set for axis tics.
+	New demo nonlinear6.dem exercises this feature and also shows the use of
+	"set tics rangelimit" with log-scaled axes.
+	Bug #1971
+
 2017-09-21  Ethan A Merritt  <[email protected]>
 
 	* term/cairo.trm (cairotrm_reset):  Still trying to get this right.

demo/all.dem

@@ -1,5 +1,5 @@
 #
-# $Id: all.dem,v 1.79 2017-01-11 04:13:58 sfeam Exp $
+# $Id: all.dem,v 1.80 2017-09-23 04:48:03 sfeam Exp $
 #
 # Executes all demos (OK, MOST demos) in this directory.
 # This serves as a series of unit tests for non-interactive capabilities.
@@ -390,6 +390,7 @@ load "nonlinear2.dem"
 load "nonlinear3.dem"
 load "nonlinear4.dem"
 load "nonlinear5.dem"
+load "nonlinear6.dem"
 reset
 
 print "********************** file transparent.dem *********************"

demo/nonlinear6.dem

@@ -0,0 +1,21 @@
+#
+# Logscale axis tic placement has always been problematic.
+# This demo exercises both automatic tic placement and
+# user-specified tic series.
+#
+set log y
+set log y2
+set tics nomirror
+set border 11
+set key center title "rangelimited tics" samplen -1
+
+set xrange [1:15000]
+
+set ytics 10 logscale rangelimit
+set y2tics auto rangelimit
+
+plot sample [x=2:14000] x axes x1y1 title "set ytics 10", \
+            [x=2:14000] x axes x1y2 title "set y2tics auto"
+
+pause -1 "<cr> to continue"
+reset

docs/gnuplot.doc

@@ -1,4 +1,4 @@
-C RCS $Id: gnuplot.doc,v 1.1109 2017-09-19 18:38:01 sfeam Exp $
+C RCS $Id: gnuplot.doc,v 1.1110 2017-09-23 04:48:04 sfeam Exp $
 C
 C Copyright (C) 1986 - 1993, 1998, 1999, 2000, 2001, 2004   Thomas Williams, Colin Kelley et al.
 C
@@ -13910,6 +13910,7 @@ Ffigure_multiple_keys
                   | ({"<label>"} <pos> {<level>} {,{"<label>"}...) }
                  {format "formatstring"} {font "name{,<size>}"} {{no}enhanced}
                  { numeric | timedate | geographic }
+                 {{no}logscale}
                  { rangelimited }
                  { textcolor <colorspec> }
        unset xtics
@@ -13963,10 +13964,32 @@ Ffigure_multiple_keys
  being displayed;  otherwise it has no effect.  Any previously specified tic
  frequency or position {and labels} are retained.
 
- Positions of the tics are calculated automatically by default or if the
- `autofreq` option is given; otherwise they may be specified in either of
- two forms:
+ Tic positions are calculated automatically by default or if the `autofreq`
+ option is given. 
 
+ A series of tic positions can be specified by giving either a tic interval
+ alone, or a start point, interval, and end point (see `xtics series`).
+
+ Individual tic positions can be specified individually by providing an
+ eplicit list of positions, where each position may have an associated
+ text label. See `xtics list`.
+
+ However they are specified, tics will only be plotted when in range.
+
+ Format (or omission) of the tic labels is controlled by `set format`, unless
+ the explicit text of a label is included in the `set xtics ("<label>")` form.
+
+ Minor (unlabeled) tics can be added automatically by the `set mxtics`
+ command, or at explicit positions by the `set xtics ("" <pos> 1, ...)` form.
+
+ The appearance of the tics (line style, line width etc.) is determined by the
+ border line (see `set border`), even if the tics are drawn at the axes.
+4 xtics series
+?set xtics series
+?xtics series
+ Syntax
+      set xtics <incr>
+      set xtics <start>, <incr>, <end>
  The implicit <start>, <incr>, <end> form specifies that a series of tics will
  be plotted on the axis between the values <start> and <end> with an increment
  of <incr>.  If <end> is not given, it is assumed to be infinity.  The
@@ -14003,13 +14026,22 @@ Ffigure_multiple_keys
  Make tics at 1, 100, 1e4, 1e6, 1e8.
        set logscale x; set xtics 1,100,1e8
 
- The explicit ("<label>" <pos> <level>, ...) form allows arbitrary tic
+4 xtics list
+?set xtics list
+?set xtics add
+?xtics list
+?xtics add
+ Syntax
+      set xtics {add} ("label1" <pos1> <level1>, "label2" <pos2> <level2>, ...) 
+
+ The explicit ("label" <pos> <level>, ...) form allows arbitrary tic
  positions or non-numeric tic labels.  In this form, the tics do not
  need to be listed in numerical order.  Each tic has a
- position, optionally with a label.  Note that the label is
- a string enclosed by quotes.  It may be a constant string, such as
- "hello", may contain formatting information for converting the
- position into its label, such as "%3f clients", or may be empty, "".
+ position, optionally with a label.
+
+ The label is a string enclosed by quotes or a string-valued expression.
+ It may contain formatting information for converting the position into its
+ label, such as "%3f clients", or it may be the empty string "".
  See `set format` for more information.  If no string is given, the
  default label (numerical) is used.
 
@@ -14042,17 +14074,6 @@ Ffigure_multiple_keys
 
  This will automatically generate tic marks every 0.5 along x, but will
  also add an explicit labeled tic mark at pi.
-
- However they are specified, tics will only be plotted when in range.
-
- Format (or omission) of the tic labels is controlled by `set format`, unless
- the explicit text of a label is included in the `set xtics ("<label>")` form.
-
- Minor (unlabeled) tics can be added automatically by the `set mxtics`
- command, or at explicit positions by the `set xtics ("" <pos> 1, ...)` form.
-
- The appearance of the tics (line style, line width etc.) is determined by the
- border line (see `set border`), even if the tics are drawn at the axes.
 4 xtics timedata
 ?set xtics timedata
 ?xtics timedata tics
@@ -14117,6 +14138,26 @@ Ffigure_multiple_keys
  To output degrees/minutes/seconds in a context other than axis tics, such as
  placing labels on a map, you can use the relative time format specifiers
  %tH %tM %tS for strptime.  See `time_specifiers`, `strptime`.
+4 xtics logscale
+?set xtics logscale
+?xtics logscale
+=logscale
+ If the `logscale` attribute is set for a tic series along a log-scaled axis,
+ the tic interval is interpreted as a multiplicative factor rather than a
+ constant. For example:
+      # generate a series of tics at y=20 y=200 y=2000 y=20000
+      set log y
+      set ytics 20, 10, 50000 logscale
+ Note that no tic is placed at y=50000 because it is not in the series 2*10^x.
+ If the logscale property is disabled, the tic increment will be treated as
+ an additive constant even for a log-scaled axis.  For example:
+      # generate a series of tics at y=20 y=40 y=60 ... y=200
+      set log y
+      set yrange [20:200]
+      set ytics 20 nologscale
+ The `logscale` attribute is set automatically by the `set log` command,
+ so normally you do not need this keyword unless you want to force a 
+ constant tic interval as in the second example above.
 4 xtics rangelimited
 ?set xtics rangelimited
 ?xtics rangelimited

src/axis.c

@@ -1,5 +1,5 @@
 #ifndef lint
-static char *RCSid() { return RCSid("$Id: axis.c,v 1.245 2017-09-11 03:40:51 sfeam Exp $"); }
+static char *RCSid() { return RCSid("$Id: axis.c,v 1.246 2017-09-23 04:48:04 sfeam Exp $"); }
 #endif
 
 /* GNUPLOT - axis.c */
@@ -1106,6 +1106,18 @@ gen_tics(struct axis *this, tic_callback callback)
 		    end = step * ceil(lmax / step);
 		else
 		    end = def->def.series.end;
+		if (def->logscaling) {
+		    /* This emulates earlier gnuplot versions in handling
+		     *     set log y; set ytics 10
+		     */
+		    step  = eval_link_function(this->linked_to_primary, step);
+		    end   = eval_link_function(this->linked_to_primary, end);
+		    start = eval_link_function(this->linked_to_primary, start);
+		    if (!(start > this->linked_to_primary->min))
+			start = this->linked_to_primary->min;
+		    lmin = this->linked_to_primary->min;
+		    lmax = this->linked_to_primary->max;
+		}
 	    } else {
 		start = def->def.series.start;
 		step = def->def.series.incr;
@@ -1253,8 +1265,10 @@ gen_tics(struct axis *this, tic_callback callback)
 		internal = tic;
 		user = tic;
 	    } else if (nonlinear(this)) {
-		if (def->type == TIC_COMPUTED)
-		    user = eval_link_function(this->linked_to_primary->linked_to_secondary, tic);
+		if (def->type == TIC_SERIES && def->logscaling)
+		    user = eval_link_function(this, tic);
+		else if (def->type == TIC_COMPUTED)
+		    user = eval_link_function(this, tic);
 		else
 		    user = tic;
 		internal = tic;	/* It isn't really, but this makes the range checks work */
@@ -1318,7 +1332,9 @@ gen_tics(struct axis *this, tic_callback callback)
 			}
 
 			/* This is where we finally decided to put the tic mark */
-			if (nonlinear(this) && (def->type == TIC_COMPUTED))
+			if (nonlinear(this) && (def->type == TIC_SERIES && def->logscaling))
+			    position = user;
+			else if (nonlinear(this) && (def->type == TIC_COMPUTED))
 			    position = user;
 			else
 			    position = internal;
@@ -1351,8 +1367,9 @@ gen_tics(struct axis *this, tic_callback callback)
 		    if (this->tictype == DT_TIMEDATE) {
 			mtic_user = time_tic_just(this->timelevel - 1, internal + mplace);
 			mtic_internal = mtic_user;
-		    } else if (nonlinear(this) && (def->type == TIC_COMPUTED)) {
-			/* FIXME: make up for bad calculation of ministart/ministep/miniend */
+		    } else if ((nonlinear(this) && (def->type == TIC_COMPUTED))
+			   ||  (nonlinear(this) && (def->type == TIC_SERIES && def->logscaling))) {
+			/* Make up for bad calculation of ministart/ministep/miniend */
 			double this_major = eval_link_function(this, internal);
 			double next_major = eval_link_function(this, internal+step);
 			mtic_user = this_major + mplace/miniend * (next_major - this_major);