From ba1d937dfb91b203614a6e2994b656605ed525fa Mon Sep 17 00:00:00 2001
From: Jehan <jehan@girinstud.io>
Date: Tue, 5 Jun 2018 16:00:43 +0200
Subject: [PATCH] app: properly "auto straighten" in measure tool.

In particular, this tool should not make huge rotation where the top
ends up in the bottom and it should not depend on whether we started the
measure tool from the left, right, bottom or top. This is fixed by using
atan() instead of atan2().

Also make a proper tooltip text. Help id is unneeded most likely though.
Finally do some cleaning and alignment.
---
 app/tools/gimpmeasureoptions.c |  4 +++-
 app/tools/gimpmeasuretool.c    | 19 ++++++++++---------
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/app/tools/gimpmeasureoptions.c b/app/tools/gimpmeasureoptions.c
index f8b96a7293..4d2f9f3bfa 100644
--- a/app/tools/gimpmeasureoptions.c
+++ b/app/tools/gimpmeasureoptions.c
@@ -130,7 +130,9 @@ gimp_measure_options_gui (GimpToolOptions *tool_options)
   button = gtk_button_new_with_label (_("Auto straighten"));
   gtk_box_pack_start (GTK_BOX (vbox), button, FALSE, FALSE, 0);
   gtk_widget_set_sensitive (button, FALSE);
-//  gimp_help_set_help_data (button, NULL, GIMP_HELP_PATH_STROKE);
+  gimp_help_set_help_data (button,
+                           _("Rotate the active layer using the measurement line as horizon"),
+                           NULL);
   gtk_widget_show (button);
 
   GIMP_MEASURE_OPTIONS (tool_options)->auto_straighten = button;
diff --git a/app/tools/gimpmeasuretool.c b/app/tools/gimpmeasuretool.c
index 132d3eee8e..891ec758db 100644
--- a/app/tools/gimpmeasuretool.c
+++ b/app/tools/gimpmeasuretool.c
@@ -110,7 +110,7 @@ static GimpToolGui * gimp_measure_tool_dialog_new (GimpMeasureTool       *measur
 static void     gimp_measure_tool_dialog_update   (GimpMeasureTool       *measure,
                                                    GimpDisplay           *display);
 
-static void          rotate_active_layer          (GtkWidget             *button,
+static void gimp_measure_tool_rotate_active_layer (GtkWidget             *button,
                                                    GimpMeasureTool       *measure);
 
 G_DEFINE_TYPE (GimpMeasureTool, gimp_measure_tool, GIMP_TYPE_DRAW_TOOL)
@@ -281,6 +281,7 @@ gimp_measure_tool_compass_changed (GimpToolWidget  *widget,
                                    GimpMeasureTool *measure)
 {
   GimpMeasureOptions *options = GIMP_MEASURE_TOOL_GET_OPTIONS (measure);
+
   g_object_get (widget,
                 "n-points", &measure->n_points,
                 "x1",       &measure->x[0],
@@ -362,8 +363,8 @@ gimp_measure_tool_start (GimpMeasureTool  *measure,
                          GimpDisplay      *display,
                          const GimpCoords *coords)
 {
-  GimpTool         *tool  = GIMP_TOOL (measure);
-  GimpDisplayShell *shell = gimp_display_get_shell (display);
+  GimpTool           *tool    = GIMP_TOOL (measure);
+  GimpDisplayShell   *shell   = gimp_display_get_shell (display);
   GimpMeasureOptions *options = GIMP_MEASURE_TOOL_GET_OPTIONS (tool);
 
   measure->n_points = 1;
@@ -398,7 +399,7 @@ gimp_measure_tool_start (GimpMeasureTool  *measure,
                     G_CALLBACK (gimp_measure_tool_compass_create_guides),
                     measure);
   g_signal_connect (options->auto_straighten, "clicked",
-                    G_CALLBACK (rotate_active_layer),
+                    G_CALLBACK (gimp_measure_tool_rotate_active_layer),
                     measure);
 
   tool->display = display;
@@ -410,7 +411,7 @@ static void
 gimp_measure_tool_halt (GimpMeasureTool *measure)
 {
   GimpMeasureOptions *options = GIMP_MEASURE_TOOL_GET_OPTIONS (measure);
-  GimpTool *tool = GIMP_TOOL (measure);
+  GimpTool           *tool    = GIMP_TOOL (measure);
 
   gtk_widget_set_sensitive (options->auto_straighten, FALSE);
 
@@ -421,7 +422,7 @@ gimp_measure_tool_halt (GimpMeasureTool *measure)
     gimp_draw_tool_stop (GIMP_DRAW_TOOL (measure));
 
   g_signal_handlers_disconnect_by_func (options->auto_straighten,
-                                        G_CALLBACK (rotate_active_layer),
+                                        G_CALLBACK (gimp_measure_tool_rotate_active_layer),
                                         measure);
 
   gimp_draw_tool_set_widget (GIMP_DRAW_TOOL (tool), NULL);
@@ -803,8 +804,8 @@ gimp_measure_tool_dialog_new (GimpMeasureTool *measure)
 }
 
 static void
-rotate_active_layer (GtkWidget       *button,
-                     GimpMeasureTool *measure)
+gimp_measure_tool_rotate_active_layer (GtkWidget       *button,
+                                       GimpMeasureTool *measure)
 {
   GimpMeasureOptions *options = GIMP_MEASURE_TOOL_GET_OPTIONS (measure);
   GimpDisplay        *display = GIMP_TOOL (measure)->display;
@@ -813,7 +814,7 @@ rotate_active_layer (GtkWidget       *button,
   gdouble             ax      = measure->x[1] - measure->x[0];
   gdouble             ay      = measure->y[1] - measure->y[0];
   GimpLayer          *item    = gimp_image_get_active_layer (image);
-  gdouble             angle   = atan2 (ay, ax);
+  gdouble             angle   = atan (ay / ax);
   GimpMatrix3         matrix;