add new preference widget for a number with a unit.

change Preferences > Steps to this new widget

(bzr r10177)

18 files changed, 212 insertions, 41 deletions

diff --git a/src/extension/internal/bluredge.cpp b/src/extension/internal/bluredge.cpp
index 8ec09d11e..76582ab05 100644
--- a/src/extension/internal/bluredge.cpp
+++ b/src/extension/internal/bluredge.cpp
@@ -59,7 +59,7 @@ BlurEdge::effect (Inkscape::Extension::Effect *module, Inkscape::UI::View::View
     int   steps = module->get_param_int("num-steps");
 
     Inkscape::Preferences *prefs = Inkscape::Preferences::get();
-    double old_offset = prefs->getDouble("/options/defaultoffsetwidth/value", 1.0);
+    double old_offset = prefs->getDouble("/options/defaultoffsetwidth/value", 1.0, "px");
 
     using Inkscape::Util::GSListConstIterator;
     // TODO need to properly refcount the items, at least
@@ -97,10 +97,10 @@ BlurEdge::effect (Inkscape::Extension::Effect *module, Inkscape::UI::View::View
             if (offset < 0.0) {
                 /* Doing an inset here folks */
                 offset *= -1.0;
-                prefs->setDouble("/options/defaultoffsetwidth/value", offset);
+                prefs->setDoubleUnit("/options/defaultoffsetwidth/value", offset, "px");
                 sp_action_perform(Inkscape::Verb::get(SP_VERB_SELECTION_INSET)->get_action(desktop), NULL);
             } else if (offset > 0.0) {
-                prefs->setDouble("/options/defaultoffsetwidth/value", offset);
+                prefs->setDoubleUnit("/options/defaultoffsetwidth/value", offset, "px");
                 sp_action_perform(Inkscape::Verb::get(SP_VERB_SELECTION_OFFSET)->get_action(desktop), NULL);
             }
 
@@ -110,7 +110,7 @@ BlurEdge::effect (Inkscape::Extension::Effect *module, Inkscape::UI::View::View
         Inkscape::GC::release(new_group);
     }
 
-    prefs->setDouble("/options/defaultoffsetwidth/value", old_offset);
+    prefs->setDoubleUnit("/options/defaultoffsetwidth/value", old_offset, "px");
 
     selection->clear();
     selection->add(items.begin(), items.end());
diff --git a/src/gradient-context.cpp b/src/gradient-context.cpp
index b98ae09fc..007fa549a 100644
--- a/src/gradient-context.cpp
+++ b/src/gradient-context.cpp
@@ -497,7 +497,7 @@ sp_gradient_context_root_handler(SPEventContext *event_context, GdkEvent *event)
     SPGradientContext *rc = SP_GRADIENT_CONTEXT(event_context);
 
     event_context->tolerance = prefs->getIntLimited("/options/dragtolerance/value", 0, 0, 100);
-    double const nudge = prefs->getDoubleLimited("/options/nudgedistance/value", 2, 0, 1000); // in px
+    double const nudge = prefs->getDoubleLimited("/options/nudgedistance/value", 2, 0, 1000, "px"); // in px
 
     GrDrag *drag = event_context->_grdrag;
     g_assert (drag);
diff --git a/src/pen-context.cpp b/src/pen-context.cpp
index 607bdaedc..64137d56f 100644
--- a/src/pen-context.cpp
+++ b/src/pen-context.cpp
@@ -989,7 +989,7 @@ pen_handle_key_press(SPPenContext *const pc, GdkEvent *event)
 
     gint ret = FALSE;
     Inkscape::Preferences *prefs = Inkscape::Preferences::get();
-    gdouble const nudge = prefs->getDoubleLimited("/options/nudgedistance/value", 2, 0, 1000); // in px
+    gdouble const nudge = prefs->getDoubleLimited("/options/nudgedistance/value", 2, 0, 1000, "px"); // in px
 
     switch (get_group0_keyval (&event->key)) {
 
diff --git a/src/preferences-skeleton.h b/src/preferences-skeleton.h
index 124a2ae51..62744bd53 100644
--- a/src/preferences-skeleton.h
+++ b/src/preferences-skeleton.h
@@ -238,7 +238,7 @@ static char const preferences_skeleton[] =
 "    <group id=\"trackalt\" value=\"0\" />"
 "    <group id=\"switchonextinput\" value=\"0\" />"
 "    <group id=\"useextinput\" value=\"1\" />"
-"    <group id=\"nudgedistance\" value=\"2\"/>\n"
+"    <group id=\"nudgedistance\" value=\"2px\"/>\n"
 "    <group id=\"rotationsnapsperpi\" value=\"12\"/>\n"
 "    <group id=\"cursortolerance\" value=\"8.0\"/>\n"
 "    <group id=\"dragtolerance\" value=\"4.0\"/>\n"
@@ -258,8 +258,8 @@ static char const preferences_skeleton[] =
 "       preserveblack=\"0\"\n"
 "       uri=\"\" />\n"
 "    <group id=\"savewindowgeometry\" value=\"1\"/>\n"
-"    <group id=\"defaultoffsetwidth\" value=\"2\"/>\n"
-"    <group id=\"defaultscale\" value=\"2\"/>\n"
+"    <group id=\"defaultoffsetwidth\" value=\"2px\"/>\n"
+"    <group id=\"defaultscale\" value=\"2px\"/>\n"
 "    <group id=\"maxrecentdocuments\" value=\"36\"/>\n"
 "    <group id=\"zoomincrement\" value=\"1.414213562\"/>\n"
 "    <group id=\"zoomcorrection\" value=\"1.0\" unit=\"mm\"/>\n"
diff --git a/src/preferences.cpp b/src/preferences.cpp
index 94fbc7257..444acfcac 100644
--- a/src/preferences.cpp
+++ b/src/preferences.cpp
@@ -23,6 +23,7 @@
 #include "xml/node-observer.h"
 #include "xml/node-iterators.h"
 #include "xml/attribute-record.h"
+#include "util/units.h"
 
 #define PREFERENCES_FILE_NAME "preferences.xml"
 
@@ -452,6 +453,22 @@ void Preferences::setDouble(Glib::ustring const &pref_path, double value)
     _setRawValue(pref_path, buf);
 }
 
+/**
+ * Set a floating point attribute of a preference.
+ *
+ * @param pref_path Path of the preference to modify.
+ * @param value The new value of the pref attribute.
+ * @param unit_abbr The string of the unit (abbreviated).
+ */
+void Preferences::setDoubleUnit(Glib::ustring const &pref_path, double value, Glib::ustring const &unit_abbr)
+{
+    gchar buf[G_ASCII_DTOSTR_BUF_SIZE];
+    g_ascii_dtostr(buf, G_ASCII_DTOSTR_BUF_SIZE, value);
+    Glib::ustring str(buf);
+    str += unit_abbr;
+    _setRawValue(pref_path, str.c_str());
+}
+
 void Preferences::setColor(Glib::ustring const &pref_path, guint32 value)
 {
     gchar buf[16];
@@ -745,11 +762,38 @@ double Preferences::_extractDouble(Entry const &v)
     return g_ascii_strtod(s, NULL);
 }
 
+double Preferences::_extractDouble(Entry const &v, Glib::ustring const &requested_unit)
+{
+    static Inkscape::Util::UnitTable unit_table; // load the unit_table once by making it static
+
+    double val = _extractDouble(v);
+    Glib::ustring unit = _extractUnit(v);
+
+    return val * (unit_table.getUnit(unit).factor / unit_table.getUnit(requested_unit).factor);
+}
+
 Glib::ustring Preferences::_extractString(Entry const &v)
 {
     return Glib::ustring(static_cast<gchar const *>(v._value));
 }
 
+Glib::ustring Preferences::_extractUnit(Entry const &v)
+{
+    gchar const *str = static_cast<gchar const *>(v._value);
+    gchar const *e;
+    g_ascii_strtod(str, (char **) &e);
+    if (e == str) {
+        return "";
+    }
+
+    if (e[0] == 0) {
+        /* Unitless */
+        return "";
+    } else {
+        return Glib::ustring(e);
+    }
+}
+
 guint32 Preferences::_extractColor(Entry const &v)
 {
     gchar const *s = static_cast<gchar const *>(v._value);
diff --git a/src/preferences.h b/src/preferences.h
index c79a7377d..64bb6ac4f 100644
--- a/src/preferences.h
+++ b/src/preferences.h
@@ -159,9 +159,10 @@ public:
         /**
          * Interpret the preference as a floating point value.
          *
-         * @param def Default value if the preference is not set.
+         * @param def  Default value if the preference is not set.
+         * @param unit Specifies the unit of the returned result. Will be ignored when equal to "". If the preference has no unit set, the default unit will be assumed.
          */
-        inline double getDouble(double def=0.0) const;
+        inline double getDouble(double def=0.0, Glib::ustring const &unit = "") const;
 
         /**
          * Interpret the preference as a limited floating point value.
@@ -172,8 +173,9 @@ public:
          * @param def Default value if the preference is not set.
          * @param min Minimum value allowed to return.
          * @param max Maximum value allowed to return.
+         * @param unit Specifies the unit of the returned result. Will be ignored when equal to "". If the preference has no unit set, the default unit will be assumed.
          */
-        inline double getDoubleLimited(double def=0.0, double min=DBL_MIN, double max=DBL_MAX) const;
+        inline double getDoubleLimited(double def=0.0, double min=DBL_MIN, double max=DBL_MAX, Glib::ustring const &unit = "") const;
 
         /**
          * Interpret the preference as an UTF-8 string.
@@ -182,6 +184,11 @@ public:
          */
         inline Glib::ustring getString() const;
 
+       /**
+         * Interpret the preference as a number followed by a unit (without space), and return this unit string.
+         */
+        inline Glib::ustring getUnit() const;
+
         /**
          * Interpret the preference as an RGBA color value.
          */
@@ -316,8 +323,8 @@ public:
         return getEntry(pref_path).getIntLimited(def, min, max);
     }
 
-    double getDouble(Glib::ustring const &pref_path, double def=0.0) {
-        return getEntry(pref_path).getDouble(def);
+    double getDouble(Glib::ustring const &pref_path, double def=0.0, Glib::ustring const &unit = "") {
+        return getEntry(pref_path).getDouble(def, unit);
     }
 
     /**
@@ -330,9 +337,10 @@ public:
      * @param def The default value to return if the preference is not set.
      * @param min Minimum value to return.
      * @param max Maximum value to return.
+     * @param unit Specifies the unit of the returned result. Will be ignored when equal to "". If the preference has no unit set, the default unit will be assumed.
      */
-    double getDoubleLimited(Glib::ustring const &pref_path, double def=0.0, double min=DBL_MIN, double max=DBL_MAX) {
-        return getEntry(pref_path).getDoubleLimited(def, min, max);
+    double getDoubleLimited(Glib::ustring const &pref_path, double def=0.0, double min=DBL_MIN, double max=DBL_MAX, Glib::ustring const &unit = "") {
+        return getEntry(pref_path).getDoubleLimited(def, min, max, unit);
     }
 
     /**
@@ -344,6 +352,15 @@ public:
         return getEntry(pref_path).getString();
     }
 
+    /**
+     * Retrieve the unit string.
+     *
+     * @param pref_path Path to the retrieved preference.
+     */
+    Glib::ustring getUnit(Glib::ustring const &pref_path) {
+        return getEntry(pref_path).getUnit();
+    }
+
     guint32 getColor(Glib::ustring const &pref_path, guint32 def=0x000000ff) {
         return getEntry(pref_path).getColor(def);
     }
@@ -399,6 +416,11 @@ public:
     void setDouble(Glib::ustring const &pref_path, double value);
 
     /**
+     * Set a floating point value with unit.
+     */
+    void setDoubleUnit(Glib::ustring const &pref_path, double value, Glib::ustring const &unit_abbr);
+
+    /**
      * Set an UTF-8 string value.
      */
     void setString(Glib::ustring const &pref_path, Glib::ustring const &value);
@@ -484,7 +506,9 @@ protected:
     bool _extractBool(Entry const &v);
     int _extractInt(Entry const &v);
     double _extractDouble(Entry const &v);
+    double _extractDouble(Entry const &v, Glib::ustring const &requested_unit);
     Glib::ustring _extractString(Entry const &v);
+    Glib::ustring _extractUnit(Entry const &v);
     guint32 _extractColor(Entry const &v);
     SPCSSAttr *_extractStyle(Entry const &v);
     SPCSSAttr *_extractInheritedStyle(Entry const &v);
@@ -566,21 +590,28 @@ inline int Preferences::Entry::getIntLimited(int def, int min, int max) const
     }
 }
 
-inline double Preferences::Entry::getDouble(double def) const
+inline double Preferences::Entry::getDouble(double def, Glib::ustring const &unit) const
 {
     if (!this->isValid()) {
         return def;
-    } else {
+    } else if (unit.length() == 0) {
         return Inkscape::Preferences::get()->_extractDouble(*this);
+    } else {
+        return Inkscape::Preferences::get()->_extractDouble(*this, unit);
     }
 }
 
-inline double Preferences::Entry::getDoubleLimited(double def, double min, double max) const
+inline double Preferences::Entry::getDoubleLimited(double def, double min, double max, Glib::ustring const &unit) const
 {
     if (!this->isValid()) {
         return def;
     } else {
-        double val = Inkscape::Preferences::get()->_extractDouble(*this);
+        double val = def;
+        if (unit.length() == 0) {
+            val = Inkscape::Preferences::get()->_extractDouble(*this);
+        } else {
+            val = Inkscape::Preferences::get()->_extractDouble(*this, unit);
+        }
         return ( val >= min && val <= max ? val : def );
     }
 }
@@ -594,6 +625,15 @@ inline Glib::ustring Preferences::Entry::getString() const
     }
 }
 
+inline Glib::ustring Preferences::Entry::getUnit() const
+{
+    if (!this->isValid()) {
+        return "";
+    } else {
+        return Inkscape::Preferences::get()->_extractUnit(*this);
+    }
+}
+
 inline guint32 Preferences::Entry::getColor(guint32 def) const
 {
     if (!this->isValid()) {
diff --git a/src/select-context.cpp b/src/select-context.cpp
index e6d78975b..640aae9ee 100644
--- a/src/select-context.cpp
+++ b/src/select-context.cpp
@@ -867,8 +867,8 @@ sp_select_context_root_handler(SPEventContext *event_context, GdkEvent *event)
             }
 			}
 
-            gdouble const nudge = prefs->getDoubleLimited("/options/nudgedistance/value", 2, 0, 1000); // in px
-			gdouble const offset = prefs->getDoubleLimited("/options/defaultscale/value", 2, 0, 1000);
+            gdouble const nudge = prefs->getDoubleLimited("/options/nudgedistance/value", 2, 0, 1000, "px"); // in px
+			gdouble const offset = prefs->getDoubleLimited("/options/defaultscale/value", 2, 0, 1000, "px");
 			int const snaps = prefs->getInt("/options/rotationsnapsperpi/value", 12);
 
 			switch (get_group0_keyval (&event->key)) {
diff --git a/src/splivarot.cpp b/src/splivarot.cpp
index 0e27ce26d..ac2acf330 100644
--- a/src/splivarot.cpp
+++ b/src/splivarot.cpp
@@ -1264,7 +1264,7 @@ void
 sp_selected_path_offset(SPDesktop *desktop)
 {
     Inkscape::Preferences *prefs = Inkscape::Preferences::get();
-    double prefOffset = prefs->getDouble("/options/defaultoffsetwidth/value", 1.0);
+    double prefOffset = prefs->getDouble("/options/defaultoffsetwidth/value", 1.0, "px");
 
     sp_selected_path_do_offset(desktop, true, prefOffset);
 }
@@ -1272,7 +1272,7 @@ void
 sp_selected_path_inset(SPDesktop *desktop)
 {
     Inkscape::Preferences *prefs = Inkscape::Preferences::get();
-    double prefOffset = prefs->getDouble("/options/defaultoffsetwidth/value", 1.0);
+    double prefOffset = prefs->getDouble("/options/defaultoffsetwidth/value", 1.0, "px");
 
     sp_selected_path_do_offset(desktop, false, prefOffset);
 }
@@ -1398,7 +1398,7 @@ sp_selected_path_create_offset_object(SPDesktop *desktop, int expand, bool updat
 
         {
             Inkscape::Preferences *prefs = Inkscape::Preferences::get();
-            o_width = prefs->getDouble("/options/defaultoffsetwidth/value", 1.0);
+            o_width = prefs->getDouble("/options/defaultoffsetwidth/value", 1.0, "px");
         }
 
         if (o_width < 0.01)
diff --git a/src/ui/dialog/inkscape-preferences.cpp b/src/ui/dialog/inkscape-preferences.cpp
index 7963dd512..81bd4dba0 100644
--- a/src/ui/dialog/inkscape-preferences.cpp
+++ b/src/ui/dialog/inkscape-preferences.cpp
@@ -249,17 +249,17 @@ void InkscapePreferences::initPageSteps()
 {
     this->AddPage(_page_steps, _("Steps"), PREFS_PAGE_STEPS);
 
-    _steps_arrow.init ( "/options/nudgedistance/value", 0.0, 1000.0, 0.01, 1.0, 2.0, false, false);
+    _steps_arrow.init ( "/options/nudgedistance/value", 0.0, 1000.0, 0.01, 2.0, UNIT_TYPE_LINEAR, "px");
     //nudgedistance is limited to 1000 in select-context.cpp: use the same limit here
-    _page_steps.add_line( false, _("Arrow keys move by:"), _steps_arrow, _("px"),
-                          _("Pressing an arrow key moves selected object(s) or node(s) by this distance (in px units)"), false);
-    _steps_scale.init ( "/options/defaultscale/value", 0.0, 1000.0, 0.01, 1.0, 2.0, false, false);
+    _page_steps.add_line( false, _("Arrow keys move by:"), _steps_arrow, "",
+                          _("Pressing an arrow key moves selected object(s) or node(s) by this distance"), false);
+    _steps_scale.init ( "/options/defaultscale/value", 0.0, 1000.0, 0.01, 2.0, UNIT_TYPE_LINEAR, "px");
     //defaultscale is limited to 1000 in select-context.cpp: use the same limit here
-    _page_steps.add_line( false, _("> and < scale by:"), _steps_scale, _("px"),
-                          _("Pressing > or < scales selection up or down by this increment (in px units)"), false);
-    _steps_inset.init ( "/options/defaultoffsetwidth/value", 0.0, 3000.0, 0.01, 1.0, 2.0, false, false);
-    _page_steps.add_line( false, _("Inset/Outset by:"), _steps_inset, _("px"),
-                          _("Inset and Outset commands displace the path by this distance (in px units)"), false);
+    _page_steps.add_line( false, _("> and < scale by:"), _steps_scale, "",
+                          _("Pressing > or < scales selection up or down by this increment"), false);
+    _steps_inset.init ( "/options/defaultoffsetwidth/value", 0.0, 3000.0, 0.01, 2.0, UNIT_TYPE_LINEAR, "px");
+    _page_steps.add_line( false, _("Inset/Outset by:"), _steps_inset, "",
+                          _("Inset and Outset commands displace the path by this distance"), false);
     _steps_compass.init ( _("Compass-like display of angles"), "/options/compassangledisplay/value", true);
     _page_steps.add_line( false, "", _steps_compass, "",
                             _("When on, angles are displayed with 0 at north, 0 to 360 range, positive clockwise; otherwise with 0 at east, -180 to 180 range, positive counterclockwise"));
diff --git a/src/ui/dialog/inkscape-preferences.h b/src/ui/dialog/inkscape-preferences.h
index a20278551..eede9eafe 100644
--- a/src/ui/dialog/inkscape-preferences.h
+++ b/src/ui/dialog/inkscape-preferences.h
@@ -178,10 +178,10 @@ protected:
 
     UI::Widget::PrefCombo       _steps_rot_snap;
     UI::Widget::PrefCheckButton _steps_compass;
-    UI::Widget::PrefSpinButton _steps_arrow;
-    UI::Widget::PrefSpinButton _steps_scale;
-    UI::Widget::PrefSpinButton _steps_inset;
-    UI::Widget::PrefSpinButton _steps_zoom;
+    UI::Widget::PrefSpinUnit    _steps_arrow;
+    UI::Widget::PrefSpinUnit    _steps_scale;
+    UI::Widget::PrefSpinUnit    _steps_inset;
+    UI::Widget::PrefSpinButton  _steps_zoom;
 
     UI::Widget::PrefRadioButton _t_sel_trans_obj;
     UI::Widget::PrefRadioButton _t_sel_trans_outl;
diff --git a/src/ui/tool/control-point-selection.cpp b/src/ui/tool/control-point-selection.cpp
index 1fb98d78f..13da4a712 100644
--- a/src/ui/tool/control-point-selection.cpp
+++ b/src/ui/tool/control-point-selection.cpp
@@ -432,7 +432,7 @@ bool ControlPointSelection::_keyboardMove(GdkEventKey const &event, Geom::Point
         delta /= _desktop->current_zoom();
     } else {
         Inkscape::Preferences *prefs = Inkscape::Preferences::get();
-        double nudge = prefs->getDoubleLimited("/options/nudgedistance/value", 2, 0, 1000);
+        double nudge = prefs->getDoubleLimited("/options/nudgedistance/value", 2, 0, 1000, "px");
         delta *= nudge;
     }
 
@@ -533,7 +533,7 @@ bool ControlPointSelection::_keyboardScale(GdkEventKey const &event, int dir)
         length_change = 1.0 / _desktop->current_zoom() * dir;
     } else {
         Inkscape::Preferences *prefs = Inkscape::Preferences::get();
-        length_change = prefs->getDoubleLimited("/options/defaultscale/value", 2, 1, 1000);
+        length_change = prefs->getDoubleLimited("/options/defaultscale/value", 2, 1, 1000, "px");
         length_change *= dir;
     }
     double scale = (maxext + length_change) / maxext;
diff --git a/src/ui/tool/path-manipulator.cpp b/src/ui/tool/path-manipulator.cpp
index 7c2013872..52286c6cc 100644
--- a/src/ui/tool/path-manipulator.cpp
+++ b/src/ui/tool/path-manipulator.cpp
@@ -727,7 +727,7 @@ void PathManipulator::scaleHandle(Node *n, int which, int dir, bool pixel)
         length_change = 1.0 / _desktop->current_zoom() * dir;
     } else {
         Inkscape::Preferences *prefs = Inkscape::Preferences::get();
-        length_change = prefs->getDoubleLimited("/options/defaultscale/value", 2, 1, 1000);
+        length_change = prefs->getDoubleLimited("/options/defaultscale/value", 2, 1, 1000, "px");
         length_change *= dir;
     }
 
diff --git a/src/ui/widget/preferences-widget.cpp b/src/ui/widget/preferences-widget.cpp
index f92e2518d..9cf80153a 100644
--- a/src/ui/widget/preferences-widget.cpp
+++ b/src/ui/widget/preferences-widget.cpp
@@ -255,6 +255,45 @@ void PrefSpinButton::on_value_changed()
     }
 }
 
+void PrefSpinUnit::init(Glib::ustring const &prefs_path,
+              double lower, double upper, double step_increment,
+              double default_value, UnitType unit_type, Glib::ustring const &default_unit)
+{
+    _prefs_path = prefs_path;
+    _is_percent = (unit_type == UNIT_TYPE_DIMENSIONLESS);
+
+    setUnitType(unit_type);
+    setUnit(default_unit);
+    setRange (lower, upper); /// @fixme  this disregards changes of units
+    setIncrements (step_increment, 0);
+    if (step_increment < 0.1) {
+        setDigits(4);
+    } else {
+        setDigits(2);
+    }
+
+    Inkscape::Preferences *prefs = Inkscape::Preferences::get();
+    double value = prefs->getDoubleLimited(prefs_path, default_value, lower, upper);
+    Glib::ustring unitstr = prefs->getUnit(prefs_path);
+    if (unitstr.length() == 0) {
+        unitstr = default_unit;
+        // write the assumed unit to preferences:
+        prefs->setDoubleUnit(_prefs_path, value, unitstr);
+    }
+    setValue(value, unitstr);
+
+    signal_value_changed().connect_notify(sigc::mem_fun(*this, &PrefSpinUnit::on_my_value_changed));
+}
+
+void PrefSpinUnit::on_my_value_changed()
+{
+    Inkscape::Preferences *prefs = Inkscape::Preferences::get();
+    if (getWidget()->is_visible()) //only take action if user changed value
+    {
+        prefs->setDoubleUnit(_prefs_path, getValue(getUnit().abbr), getUnit().abbr);
+    }
+}
+
 const double ZoomCorrRuler::textsize = 7;
 const double ZoomCorrRuler::textpadding = 5;
 
diff --git a/src/ui/widget/preferences-widget.h b/src/ui/widget/preferences-widget.h
index 758ab38cd..6caab11ae 100644
--- a/src/ui/widget/preferences-widget.h
+++ b/src/ui/widget/preferences-widget.h
@@ -33,6 +33,7 @@
 #include "ui/widget/color-picker.h"
 #include "ui/widget/unit-menu.h"
 #include "ui/widget/spinbutton.h"
+#include "ui/widget/scalar-unit.h"
 
 namespace Inkscape {
 namespace UI {
@@ -82,6 +83,21 @@ protected:
     void on_value_changed();
 };
 
+class PrefSpinUnit : public ScalarUnit
+{
+public:
+    PrefSpinUnit() : ScalarUnit("", "") {};
+
+    void init(Glib::ustring const &prefs_path,
+              double lower, double upper, double step_increment,
+              double default_value,
+              UnitType unit_type, Glib::ustring const &default_unit);
+protected:
+    Glib::ustring _prefs_path;
+    bool _is_percent;
+    void on_my_value_changed();
+};
+
 class ZoomCorrRuler : public Gtk::DrawingArea {
 public:
     ZoomCorrRuler(int width = 100, int height = 20);
diff --git a/src/ui/widget/scalar-unit.cpp b/src/ui/widget/scalar-unit.cpp
index e713f3e06..1c0fdff68 100644
--- a/src/ui/widget/scalar-unit.cpp
+++ b/src/ui/widget/scalar-unit.cpp
@@ -130,6 +130,22 @@ ScalarUnit::setUnit(Glib::ustring const &unit) {
     return true;
 }
 
+/** Adds the unit type to the ScalarUnit widget */
+void
+ScalarUnit::setUnitType(UnitType unit_type) {
+    g_assert(_unit_menu != NULL);
+    _unit_menu->setUnitType(unit_type);
+    lastUnits = _unit_menu->getUnitAbbr();
+}
+
+/** Resets the unit type for the ScalarUnit widget */
+void
+ScalarUnit::resetUnitType(UnitType unit_type) {
+    g_assert(_unit_menu != NULL);
+    _unit_menu->resetUnitType(unit_type);
+    lastUnits = _unit_menu->getUnitAbbr();
+}
+
 /** Gets the object for the currently selected unit */
 Unit
 ScalarUnit::getUnit() const {
diff --git a/src/ui/widget/scalar-unit.h b/src/ui/widget/scalar-unit.h
index 4e08d63f4..ed3728e69 100644
--- a/src/ui/widget/scalar-unit.h
+++ b/src/ui/widget/scalar-unit.h
@@ -45,6 +45,8 @@ public:
     double    getValue(Glib::ustring const &units) const;
 
     bool      setUnit(Glib::ustring const &units);
+    void      setUnitType(UnitType unit_type);
+    void      resetUnitType(UnitType unit_type);
     void      setValue(double number, Glib::ustring const &units);
     void      setValueKeepUnit(double number, Glib::ustring const &units);
     void      setValue(double number);
diff --git a/src/ui/widget/unit-menu.cpp b/src/ui/widget/unit-menu.cpp
index b4271762c..5c68f7196 100644
--- a/src/ui/widget/unit-menu.cpp
+++ b/src/ui/widget/unit-menu.cpp
@@ -54,6 +54,19 @@ UnitMenu::setUnitType(UnitType unit_type)
     return true;
 }
 
+/** Removes all unit entries, then adds the unit type to the widget.
+    This extracts the corresponding
+    units from the unit map matching the given type, and appends them
+    to the dropdown widget.  It causes the primary unit for the given
+    unit_type to be selected.  */
+bool
+UnitMenu::resetUnitType(UnitType unit_type) 
+{
+    clear_text();
+
+    return setUnitType(unit_type);
+}
+
 /** Returns the Unit object corresponding to the current selection
     in the dropdown widget */
 Unit
diff --git a/src/ui/widget/unit-menu.h b/src/ui/widget/unit-menu.h
index 60a9702b4..efeb10ead 100644
--- a/src/ui/widget/unit-menu.h
+++ b/src/ui/widget/unit-menu.h
@@ -28,6 +28,7 @@ public:
     virtual ~UnitMenu();
 
     bool          setUnitType(UnitType unit_type);
+    bool          resetUnitType(UnitType unit_type);
 
     bool          setUnit(Glib::ustring const &unit);