[gimp] app: improve precision of paint tools' straight line distance...

[Jehan Pagès <jehanp src gnome org>]

commit 1835b2ae61d69abc32fa61f54d73b5ca79f0aca6
Author: Jehan <jehan girinstud io>
Date:   Thu Jan 19 17:29:59 2017 +0100

    app: improve precision of paint tools' straight line distance...
    
    ... in status bar.
    Follow-up of commits f836892 and d1c3c3d. With high resolutions, the
    distance displayed in the status bar when shift-clicking in a paint tool
    may lack digit precision and show the same value (in non-pixel unit) for
    several consecutive pixels. Compute a more accurate precision than what
    gimp_unit_get_digits() can provide in such cases.

 app/tools/gimppainttool.c |   27 ++++++++++++++++++---------
 1 files changed, 18 insertions(+), 9 deletions(-)
---
diff --git a/app/tools/gimppainttool.c b/app/tools/gimppainttool.c
index d1341dc..5434668 100644
--- a/app/tools/gimppainttool.c
+++ b/app/tools/gimppainttool.c
@@ -642,7 +642,7 @@ gimp_paint_tool_oper_update (GimpTool         *tool,
            */
 
           gchar   *status_help;
-          gdouble  dx, dy, dist;
+          gdouble  dx, dy, pixel_dist;
 
           gimp_paint_core_round_line (core, paint_options,
                                       (state & constrain_mask) != 0);
@@ -656,30 +656,39 @@ gimp_paint_tool_oper_update (GimpTool         *tool,
                                                 _("%s for constrained angles"),
                                                 NULL);
 
+          pixel_dist = sqrt (SQR (dx) + SQR (dy));
+
           /*  show distance in statusbar  */
           if (shell->unit == GIMP_UNIT_PIXEL)
             {
-              dist = sqrt (SQR (dx) + SQR (dy));
-
               gimp_tool_push_status (tool, display, "%.1f %s.  %s",
-                                     dist, _("pixels"), status_help);
+                                     pixel_dist, _("pixels"), status_help);
             }
           else
             {
               gdouble xres;
               gdouble yres;
+              gdouble dist;
+              gint    digits;
               gchar   format_str[64];
 
+              /* The distance in unit. */
               gimp_image_get_resolution (image, &xres, &yres);
-
-              g_snprintf (format_str, sizeof (format_str), "%%.%df %s.  %%s",
-                          gimp_unit_get_digits (shell->unit),
-                          gimp_unit_get_symbol (shell->unit));
-
               dist = (gimp_unit_get_factor (shell->unit) *
                       sqrt (SQR (dx / xres) +
                             SQR (dy / yres)));
 
+              /* The ideal digit precision for unit in current resolution. */
+              digits = gimp_unit_get_digits (shell->unit);
+              if (dist > 0.0)
+                {
+                  digits = MAX (ceil (log10 (pixel_dist / dist)),
+                                digits);
+                }
+
+              g_snprintf (format_str, sizeof (format_str), "%%.%df %s.  %%s",
+                          digits, gimp_unit_get_symbol (shell->unit));
+
               gimp_tool_push_status (tool, display, format_str,
                                      dist, status_help);
             }