#2181 ylabel positioning regression

[Markus Ebner]

I just got upgraded from gnuplot 5.2.6 to gnuplot Version 5.2 patchlevel 7 last modified 2019-05-29.

There seems to be a regression for the positioning of ylabels. I attached multiple examples: a LaTeX/tikz example, and a gnuplot file I tested with the qt-backend).
However, there seem to be different causes for different backends:
While xtics and ytics are enabled, everything seemed to work fine with the qt-backend, only disabling them caused it here. The tikz example, on the other hand, shows the bug with either xtics & ytics enabled or disabled.

[Karl Ratzsch]

Much simpler example with wxt or qt terminal

 set ylabel "ylabel"
 unset ytics
 plot x

The ylabel sits tightly on the left border, with the lower end of the "y" (depending on the font i guess) even sticking into the graph. (qt need plotting twice, the first try looks terrible due to the slow font initialisation problem)

[Ethan Merritt]

Karl: that test case may expose a separate but clearly related bug, or at least an unexpected outcome. Why is there a difference in placement between "unset ytics" and "set ytics format '' scale 0.0"?

[Ethan Merritt]

I fear this is a lose/lose decision. The y label positioning was causing problems for some people in versions 5.0 and 5.2 (E.g. bugs 2048 2052 2165). Even on systems not obviously suffering from those bugs, some terminals were placing the ylabel so close to the left edge of the canvas that text markup or changes in font size pushed it partially off the edge. So commit 3df39e tried to clean this up. Part of that was shifting placement of the rotated ylabel a partial character unit to the right (closer to the axis). Now this current bug points out that for some terminals the revised ylabel placement in 5.2.7 puts it too close to the plot, at least if there are no ytic labels. Again the severity is terminal-dependent.

So what to do?

• shift the placement back to the left by some fraction of a character height?
• make the placement terminal-dependent?
• increase the default left margin on the page?
• add a new command option to optional do one or more of the above?
• leave the code alone but emphasize that users may need to tweak placement by setting an offset or by adding an extra newline before and/or after the ylabel text?

If you want to experiment, this is the relevant line of code:

diff --git a/src/boundary.c b/src/boundary.c
index 861061c..1bb21a8 100644
--- a/src/boundary.c
+++ b/src/boundary.c
@@ -1431,7 +1431,8 @@ draw_titles()
     if (axis_array[FIRST_Y_AXIS].label.text) {
        int x = ylabel_x;
        int y = (plot_bounds.ytop + plot_bounds.ybot) / 2;

-    x += t->h_char;
+    /* There has been much argument about the optimal ylabel position */
+    x += t->h_char / 4.;
        write_label(x, y, &(axis_array[FIRST_Y_AXIS].label));
        reset_textcolor(&(axis_array[FIRST_Y_AXIS].label.textcolor));
     }

Also:
It is quite possible that the terminals with least amount of space between the label and the plot border have a separate bug that gets the vertical justification of the rotated text wrong.