[gimp/gimp-2-10] app: new gimp_spin_scale_set_constrain_drag() and use it on paint...

[Jehan <jehanp src gnome org>]

commit ffe2fb478ca2bfb7adf0d5c3d556221db18cd8f9
Author: Jehan <jehan girinstud io>
Date:   Fri Jan 25 18:21:05 2019 +0100

    app: new gimp_spin_scale_set_constrain_drag() and use it on paint...
    
    ... tools' brush options.
    After discussions, it turned out that many people disliked that the spin
    scale for brush size (and some other options) get you fractional values.
    How often do you actually need to get a 4.32 pixel-size brush? And even
    how meaningful is it? On the other hand, you usually want a 4 or a 5
    pixel size brush and it's nearly impossible to get (exactly) by dragging
    the scale widget.
    It is so annoying that some even resort to edit the value with keyboard!
    So I am adding an optional "constrain" feature to GimpSpinScale. It will
    still be possible to get fractional values when constraining is on, for
    instance with keyboard edit (the arrow incrementation also will keep any
    fractional part). So the interaction for such scales is simply reversed
    so that you get integers easily, and fractional parts with a bit more
    effort.
    
    It is not turned on by default (some feature actually need precision and
    we don't want to break the sliders for these) and for the time being, I
    only applied it to all the brush settings in paint tools. Now that it
    exist, we may want to apply this to more scales in various parts of
    GIMP.
    
    (cherry picked from commit bff3903f377ea26471c00bff132c5dbb99b04c29)

 app/tools/gimppaintoptions-gui.c |  2 ++
 app/widgets/gimpspinscale.c      | 37 +++++++++++++++++++++++++++++++++++++
 app/widgets/gimpspinscale.h      |  3 +++
 3 files changed, 42 insertions(+)
---
diff --git a/app/tools/gimppaintoptions-gui.c b/app/tools/gimppaintoptions-gui.c
index 7955438ef7..23aef019e6 100644
--- a/app/tools/gimppaintoptions-gui.c
+++ b/app/tools/gimppaintoptions-gui.c
@@ -524,6 +524,8 @@ gimp_paint_options_gui_scale_with_buttons (GObject      *config,
 
   scale = gimp_prop_spin_scale_new (config, prop_name, NULL,
                                     step_increment, page_increment, digits);
+  gimp_spin_scale_set_constrain_drag (GIMP_SPIN_SCALE (scale), TRUE);
+
   gimp_prop_widget_set_factor (scale, factor,
                                step_increment, page_increment, digits);
   gimp_spin_scale_set_scale_limits (GIMP_SPIN_SCALE (scale),
diff --git a/app/widgets/gimpspinscale.c b/app/widgets/gimpspinscale.c
index 2b11e1b9b4..31769a6693 100644
--- a/app/widgets/gimpspinscale.c
+++ b/app/widgets/gimpspinscale.c
@@ -62,6 +62,8 @@ struct _GimpSpinScalePrivate
   guint            mnemonic_keyval;
   gboolean         mnemonics_visible;
 
+  gboolean         constrain_drag;
+
   gboolean         scale_limits_set;
   gdouble          scale_lower;
   gdouble          scale_upper;
@@ -721,6 +723,9 @@ gimp_spin_scale_change_value (GtkWidget *widget,
   value = RINT (value);
   value /= power;
 
+  if (private->constrain_drag)
+    value = rint (value);
+
   gtk_adjustment_set_value (adjustment, value);
 }
 
@@ -1338,3 +1343,35 @@ gimp_spin_scale_get_gamma (GimpSpinScale *scale)
 
   return GET_PRIVATE (scale)->gamma;
 }
+
+/**
+ * gimp_spin_scale_set_constrain_drag:
+ * @scale: the #GimpSpinScale.
+ * @constrain: whether constraining to integer values when dragging with
+ *             pointer.
+ *
+ * If @constrain_drag is TRUE, dragging the scale with the pointer will
+ * only result into integer values. It will still possible to set the
+ * scale to fractional values (if the spin scale "digits" is above 0)
+ * for instance with keyboard edit.
+ */
+void
+gimp_spin_scale_set_constrain_drag (GimpSpinScale *scale,
+                                    gboolean       constrain)
+{
+  GimpSpinScalePrivate *private;
+
+  g_return_if_fail (GIMP_IS_SPIN_SCALE (scale));
+
+  private = GET_PRIVATE (scale);
+
+  private->constrain_drag = constrain;
+}
+
+gboolean
+gimp_spin_scale_get_constrain_drag (GimpSpinScale *scale)
+{
+  g_return_val_if_fail (GIMP_IS_SPIN_SCALE (scale), 1.0);
+
+  return GET_PRIVATE (scale)->constrain_drag;
+}
diff --git a/app/widgets/gimpspinscale.h b/app/widgets/gimpspinscale.h
index 4435cf50b0..0693ac2745 100644
--- a/app/widgets/gimpspinscale.h
+++ b/app/widgets/gimpspinscale.h
@@ -66,5 +66,8 @@ void          gimp_spin_scale_set_gamma          (GimpSpinScale *scale,
                                                   gdouble        gamma);
 gdouble       gimp_spin_scale_get_gamma          (GimpSpinScale *scale);
 
+void          gimp_spin_scale_set_constrain_drag (GimpSpinScale *scale,
+                                                  gboolean       constrain);
+gboolean      gimp_spin_scale_get_constrain_drag (GimpSpinScale *scale);
 
 #endif  /*  __GIMP_SPIN_SCALE_H__  */