Unify scale widgets API

Flip all scale based widgets to use scale denominators instead
of actual scales (ie 100.0 instead of 0.01 for 1:100).

This is done for consistency with the rest of the API, which
predominantly uses scale denominators. It also helps
precision loss as a result of multiple 1.0 / scale conversions
throughout the code.

Refs #15337

doc/api_break.dox

@@ -2010,6 +2010,32 @@ QgsScaleBarStyle        {#qgis_api_break_3_0_QgsScaleBarStyle}
 - The interface for QgsScaleBarStyle has been completely rewritten - any code using QgsScaleBarStyle or subclasses will need to update
 to the new draw() and calculateBoxSize() methods.
 
+
+QgsScaleComboBox        {#qgis_api_break_3_0_QgsScaleComboBox}
+----------------
+
+- All numeric scales reported and used by QgsScaleComboBox now represent the scale denominator (i.e. 2345 for a scale "1:2345"), for consistency with other scale use throughout the API.
+
+
+QgsScaleRangeWidget        {#qgis_api_break_3_0_QgsScaleRangeWidget}
+-------------------
+
+- All numeric scales reported and used by QgsScaleRangeWidget now represent the scale denominator (i.e. 2345 for a scale "1:2345"), for consistency with other scale use throughout the API.
+- minimumScaleDenom() and maximumScaleDenom() were removed. Now minimumScale() and maximumScale() report the scale denominator.
+
+
+QgsScaleVisibilityDialog        {#qgis_api_break_3_0_QgsScaleVisibilityDialog}
+------------------------
+
+- All numeric scales reported and used by QgsScaleVisibilityDialog now represent the scale denominator (i.e. 2345 for a scale "1:2345"), for consistency with other scale use throughout the API.
+
+
+QgsScaleWidget        {#qgis_api_break_3_0_QgsScaleWidget}
+--------------
+
+- All numeric scales reported and used by QgsScaleWidget now represent the scale denominator (i.e. 2345 for a scale "1:2345"), for consistency with other scale use throughout the API.
+
+
 QgsServer       {#qgis_api_break_3_0_QgsServer}
 ----------
 

python/auto_sip.blacklist

@@ -50,8 +50,6 @@ gui/qgsrasterformatsaveoptionswidget.sip
 gui/qgsrasterlayersaveasdialog.sip
 gui/qgsrasterpyramidsoptionswidget.sip
 gui/qgsrubberband.sip
-gui/qgsscalerangewidget.sip
-gui/qgsscalevisibilitydialog.sip
 gui/qgsscrollarea.sip
 gui/qgssearchquerybuilder.sip
 gui/qgsshortcutsmanager.sip

python/gui/qgsscalecombobox.sip

@@ -21,57 +21,90 @@ class QgsScaleComboBox : QComboBox
 #include "qgsscalecombobox.h"
 %End
   public:
-    QgsScaleComboBox( QWidget *parent /TransferThis/ = 0 );
 
-    QString scaleString();
+    QgsScaleComboBox( QWidget *parent /TransferThis/ = 0 );
 %Docstring
-Function to read the selected scale as text
+ Constructor for QgsScaleComboBox.
+%End
+
+    QString scaleString() const;
+%Docstring
+ Returns the selected scale as a string, e.g. "1:150".
+.. seealso:: setScaleString()
  :rtype: str
 %End
-    bool setScaleString( const QString &scaleTxt );
+
+    bool setScaleString( const QString &string );
 %Docstring
-Function to set the selected scale from text
+ Set the selected scale from a ``string``, e.g. "1:150".
+.. seealso:: scaleString()
  :rtype: bool
 %End
+
     double scale() const;
 %Docstring
-Function to read the selected scale as double
+ Returns the selected scale as a double.
+ The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+.. seealso:: setScale()
  :rtype: float
 %End
-    void setScale( double scale );
+
-%Docstring
-Function to set the selected scale from double
-%End
     double minScale() const;
 %Docstring
-Function to read the min scale
+ Returns the minimum scale, or 0 if no minimum scale set.
+ The ``scale`` value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+ Any scale lower than the minimum scale will automatically be converted to the minimum scale.
+ Except for 0 which is always allowed.
  :rtype: float
 %End
 
     static QString toString( double scale );
 %Docstring
+ Helper function to convert a ``scale`` double to scale string.
+ The ``scale`` value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+
+ The returned string will be rounded (e.g. 1:1000, not 1:1000.345).
+.. seealso:: toDouble()
  :rtype: str
 %End
-    static double toDouble( const QString &scaleString, bool *ok = 0 );
+
+    static double toDouble( const QString &string, bool *ok = 0 );
 %Docstring
-Helper function to convert a scale string to double
+ Helper function to convert a scale ``string`` to double.
+ The returned value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+ If specified, ``ok`` will be set to true if the string was successfully interpreted as a scale.
+.. seealso:: toString()
  :rtype: float
 %End
 
   signals:
+
     void scaleChanged( double scale );
 %Docstring
-Signal is emitted when *user* has finished editing/selecting a new scale.
+ Emitted when *user* has finished editing/selecting a new scale.
+ The ``scale`` value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
 %End
 
   public slots:
+
     void updateScales( const QStringList &scales = QStringList() );
+%Docstring
+ Sets the list of predefined ``scales`` to show in the combobox. List elements
+ are expected to be valid scale strings, such as "1:1000000".
+%End
+
+    void setScale( double scale );
+%Docstring
+ Set the selected scale from a double.
+ The ``scale`` value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+.. seealso:: scale()
+%End
 
     void setMinScale( double scale );
 %Docstring
- Set the minimum allowed scale.
+ Set the minimum allowed ``scale``. Set to 0 to disable the minimum scale.
- Anything scale lower than the minimum scale will automatically
+ The ``scale`` value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
- be converted to the minimum scale.
+ Any scale lower than the minimum scale will automatically be converted to the minimum scale.
  Except for 0 which is always allowed.
 %End
 

python/gui/qgsscalerangewidget.sip

@@ -1,49 +1,104 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/gui/qgsscalerangewidget.h                                        *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/
+
+
+
 
 class QgsScaleRangeWidget : QWidget
 {
+%Docstring
+ A widget allowing entry of a range of map scales, e.g. minimum scale and maximum scale.
+%End
+
 %TypeHeaderCode
 #include "qgsscalerangewidget.h"
 %End
-
   public:
+
     explicit QgsScaleRangeWidget( QWidget *parent /TransferThis/ = 0 );
-    ~QgsScaleRangeWidget();
+%Docstring
+ Constructor for QgsScaleRangeWidget.
+%End
 
-    //! set the map canvas which will be used for the current scale buttons
+    void setMapCanvas( QgsMapCanvas *canvas );
-    /**
+%Docstring
-     * @brief setMapCanvas set the map canvas which will be used for the current scale buttons
+ Sets the map ``canvas`` which will be used for the current scale buttons.
-     * if not set, the buttons are hidden.
+ If not set, the buttons are hidden.
-     */
+%End
-    void setMapCanvas( QgsMapCanvas *mapCanvas );
 
-    //! return the minimum scale
+    double minimumScale() const;
-    double minimumScale();
+%Docstring
+ Returns the selected minimum scale, or 0 if minimum scale is not set.
+ The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+.. seealso:: maximumScale()
+.. seealso:: setMinimumScale()
+ :rtype: float
+%End
 
-    //! return the maximum scale
+    double maximumScale() const;
-    double maximumScale();
+%Docstring
+ Returns the selected maximum scale, or 0 if maximum scale is not set.
+ The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+.. seealso:: minimumScale()
+.. seealso:: setMaximumScale()
+ :rtype: float
+%End
 
-    //! return the minimum scale denominator ( = 1 / maximum scale )
-    double minimumScaleDenom();
-
-    //! return the maximum scale denominator ( = 1 / minimum scale )
-    double maximumScaleDenom();
-
-    //! call to reload the project scales and apply them to the 2 scales combo boxes
     void reloadProjectScales();
+%Docstring
+ Call to reload the preset scales from the current project and apply them to the 2 scales combo boxes.
+%End
 
   public slots:
+
     void setMinimumScale( double scale );
+%Docstring
+ Set the minimum ``scale``, or 0 to indicate the minimum is not set.
+ The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+.. seealso:: minimumScale()
+.. seealso:: setMaximumScale()
+.. seealso:: setScaleRange()
+%End
 
     void setMaximumScale( double scale );
+%Docstring
+ Set the maximum ``scale``, or 0 to indicate the minimum is not set.
+ The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+.. seealso:: maximumScale()
+.. seealso:: setMinimumScale()
+.. seealso:: setScaleRange()
+%End
 
     void setScaleRange( double min, double max );
+%Docstring
+ Sets the scale range, from ``min`` scale to ``max`` scale.
+ The scale values indicates the scale denominator, e.g. 1000.0 for a 1:1000 map,
+ or 0 to indicate not set.
+.. seealso:: setMinimumScale()
+.. seealso:: setMaximumScale()
+%End
 
   signals:
 
-    /** Emitted when the scale range set in the widget is changed.
-     * @param min minimum scale
-     * @param max maximum scale
-     * @note added in QGIS 2.16
-     */
     void rangeChanged( double min, double max );
+%Docstring
+ Emitted when the scale range set in the widget is changed.
+ The scale values indicates the scale denominator, e.g. 1000.0 for a 1:1000 map,
+ or 0 to indicate not set.
+.. versionadded:: 2.16
+%End
+
 };
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/gui/qgsscalerangewidget.h                                        *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/

python/gui/qgsscalevisibilitydialog.sip

@@ -1,30 +1,87 @@
-class QgsScaleVisibilityDialog : QObject
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/gui/qgsscalevisibilitydialog.h                                   *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/
+
+
+
+
+class QgsScaleVisibilityDialog : QDialog
 {
-%TypeHeaderCode
+%Docstring
-#include <qgsscalevisibilitydialog.h>
+ A dialog allowing users to enter a scale visibility range.
 %End
 
+%TypeHeaderCode
+#include "qgsscalevisibilitydialog.h"
+%End
   public:
+
     explicit QgsScaleVisibilityDialog( QWidget *parent /TransferThis/ = 0, const QString &title = QString(), QgsMapCanvas *mapCanvas = 0 );
+%Docstring
+ Constructor for QgsScaleVisibilityDialog, with specified dialog ``title``. The ``mapCanvas`` argument
+ can be used to associate the dialog with a map canvas, allowing use of the current map scale
+ within the dialog.
+%End
 
-    //! return if scale visibilty is enabled
+    bool hasScaleVisibility() const;
-    bool hasScaleVisibility();
+%Docstring
+ Return true if scale based visibilty is enabled.
+ :rtype: bool
+%End
 
-    //! return minimum scale (true scale, not scale denominator)
+    double minimumScale() const;
-    double minimumScale();
+%Docstring
-
+ Returns the selected minimum scale, or 0 if minimum scale is not set.
-    //! return maximum scale (true scale, not scale denominator)
+ The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
-    double maximumScale();
+.. seealso:: maximumScale()
+.. seealso:: setMinimumScale()
+ :rtype: float
+%End
 
+    double maximumScale() const;
+%Docstring
+ Returns the selected maximum scale, or 0 if maximum scale is not set.
+ The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+.. seealso:: minimumScale()
+.. seealso:: setMaximumScale())
+ :rtype: float
+%End
 
   public slots:
-    //! set if scale visibility is enabled
+
     void setScaleVisiblity( bool hasScaleVisibility );
+%Docstring
+ Set whether scale based visibility is enabled.
+.. seealso:: hasScaleVisibility()
+%End
 
-    //! set minimum scale (true scale, not scale denominator)
+    void setMinimumScale( double scale );
-    void setMinimumScale( double minScale );
+%Docstring
+ Set the minimum ``scale``, or 0 to indicate the minimum is not set.
+ The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+.. seealso:: minimumScale()
+.. seealso:: setMaximumScale()
+%End
+
+    void setMaximumScale( double scale );
+%Docstring
+ Set the maximum ``scale``, or 0 to indicate the minimum is not set.
+ The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+.. seealso:: maximumScale()
+.. seealso:: setMinimumScale()
+%End
 
-    //! set maximum scale (true scale, not scale denominator)
-    void setMaximumScale( double maxScale );
 
 };
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/gui/qgsscalevisibilitydialog.h                                   *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/

python/gui/qgsscalewidget.sip

@@ -33,76 +33,111 @@ class QgsScaleWidget : QWidget
 
     void setShowCurrentScaleButton( bool showCurrentScaleButton );
 %Docstring
+ Sets whether to show a button to set the scale to the current scale of the map canvas next to the combobox.
 .. note::
 
    the map canvas must be defined to show the button
+.. seealso:: showCurrentScaleButton()
+.. seealso:: setMapCanvas()
 %End
+
     bool showCurrentScaleButton();
 %Docstring
-returns if a button to set the scale from map canvas is shown or not
+ Returns whether a button to set the scale from map canvas is shown or not.
+.. seealso:: setShowCurrentScaleButton()
  :rtype: bool
 %End
 
     void setMapCanvas( QgsMapCanvas *canvas );
 %Docstring
-set the map canvas associated to the current button
+ Set the map ``canvas`` associated to the current button.
 %End
 
-    QString scaleString();
+    QString scaleString() const;
 %Docstring
-Function to read the selected scale as text
+ Returns the selected scale as a string, e.g. "1:150".
+.. seealso:: setScaleString()
  :rtype: str
 %End
-    bool setScaleString( const QString &scaleTxt );
+
+    bool setScaleString( const QString &string );
 %Docstring
-Function to set the selected scale from text
+ Set the selected scale from a ``string``, e.g. "1:150".
+.. seealso:: scaleString()
  :rtype: bool
 %End
+
     double scale() const;
 %Docstring
-Function to read the selected scale as double
+ Returns the selected scale as a double.
+ The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+.. seealso:: setScale()
  :rtype: float
 %End
-    void setScale( double scale );
+
-%Docstring
-Function to set the selected scale from double
-%End
     double minScale() const;
 %Docstring
-Function to read the min scale
+ Returns the minimum scale, or 0 if no minimum scale set.
+ The ``scale`` value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+ Any scale lower than the minimum scale will automatically be converted to the minimum scale.
+ Except for 0 which is always allowed.
  :rtype: float
 %End
 
     static QString toString( double scale );
 %Docstring
+ Helper function to convert a ``scale`` double to scale string.
+ The ``scale`` value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+
+ The returned string will be rounded (e.g. 1:1000, not 1:1000.345).
+.. seealso:: toDouble()
  :rtype: str
 %End
+
     static double toDouble( const QString &scaleString, bool *ok = 0 );
 %Docstring
-Helper function to convert a scale string to double
+ Helper function to convert a scale ``string`` to double.
+ The returned value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+ If specified, ``ok`` will be set to true if the string was successfully interpreted as a scale.
+.. seealso:: toString()
  :rtype: float
 %End
 
   public slots:
+
+    void setScale( double scale );
+%Docstring
+ Set the selected scale from a double.
+ The ``scale`` value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+.. seealso:: scale()
+%End
+
     void updateScales( const QStringList &scales = QStringList() );
 %Docstring
-updates the list of predefined scales
+ Sets the list of predefined ``scales`` to show in the combobox. List elements
+ are expected to be valid scale strings, such as "1:1000000".
 %End
 
     void setScaleFromCanvas();
 %Docstring
-assign the current scale from the map canvas
+ Assigns the current scale from the map canvas, if set.
+.. seealso:: setMapCanvas()
 %End
 
     void setMinScale( double scale );
 %Docstring
-Function to set the min scale
+ Set the minimum allowed ``scale``. Set to 0 to disable the minimum scale.
+ The ``scale`` value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+ Any scale lower than the minimum scale will automatically be converted to the minimum scale.
+ Except for 0 which is always allowed.
 %End
 
   signals:
+
     void scaleChanged( double scale );
 %Docstring
-Signal is emitted when *user* has finished editing/selecting a new scale.
+ Emitted when *user* has finished editing/selecting a new scale.
+ The ``scale`` value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
 %End
 
 };

src/app/qgisapp.cpp

@@ -8979,8 +8979,8 @@ void QgisApp::setLayerScaleVisibility()
   if ( layer )
   {
     dlg->setScaleVisiblity( layer->hasScaleBasedVisibility() );
-    dlg->setMinimumScale( 1.0 / layer->minimumScale() );
+    dlg->setMinimumScale( layer->minimumScale() );
-    dlg->setMaximumScale( 1.0 / layer->maximumScale() );
+    dlg->setMaximumScale( layer->maximumScale() );
   }
   if ( dlg->exec() )
   {
@@ -8988,8 +8988,8 @@ void QgisApp::setLayerScaleVisibility()
     Q_FOREACH ( QgsMapLayer *layer, layers )
     {
       layer->setScaleBasedVisibility( dlg->hasScaleVisibility() );
-      layer->setMaximumScale( 1.0 / dlg->maximumScale() );
+      layer->setMaximumScale( dlg->maximumScale() );
-      layer->setMinimumScale( 1.0 / dlg->minimumScale() );
+      layer->setMinimumScale( dlg->minimumScale() );
     }
     freezeCanvases( false );
     refreshMapCanvas();

src/app/qgsdiagramproperties.cpp

@@ -205,7 +205,7 @@ QgsDiagramProperties::QgsDiagramProperties( QgsVectorLayer *layer, QWidget *pare
     mIncreaseMinimumSizeLabel->setEnabled( false );
     mBarWidthSpinBox->setValue( 5 );
     mScaleVisibilityGroupBox->setChecked( layer->hasScaleBasedVisibility() );
-    mScaleRangeWidget->setScaleRange( 1.0 / layer->minimumScale(), 1.0 / layer->maximumScale() ); // caution: layer uses scale denoms, widget uses true scales
+    mScaleRangeWidget->setScaleRange( layer->minimumScale(), layer->maximumScale() );
     mShowAllCheckBox->setChecked( true );
     mCheckBoxAttributeLegend->setChecked( true );
     mCheckBoxSizeLegend->setChecked( false );
@@ -265,9 +265,8 @@ QgsDiagramProperties::QgsDiagramProperties( QgsVectorLayer *layer, QWidget *pare
       mDiagramPenColorButton->setColor( settingList.at( 0 ).penColor );
       mPenWidthSpinBox->setValue( settingList.at( 0 ).penWidth );
       mDiagramSizeSpinBox->setValue( ( size.width() + size.height() ) / 2.0 );
-      // caution: layer uses scale denoms, widget uses true scales
+      mScaleRangeWidget->setScaleRange( ( settingList.at( 0 ).maxScaleDenominator > 0 ? settingList.at( 0 ).maxScaleDenominator : layer->minimumScale() ),
-      mScaleRangeWidget->setScaleRange( 1.0 / ( settingList.at( 0 ).maxScaleDenominator > 0 ? settingList.at( 0 ).maxScaleDenominator : layer->minimumScale() ),
+                                        ( settingList.at( 0 ).minScaleDenominator > 0 ? settingList.at( 0 ).minScaleDenominator : layer->maximumScale() ) );
-                                        1.0 / ( settingList.at( 0 ).minScaleDenominator > 0 ? settingList.at( 0 ).minScaleDenominator : layer->maximumScale() ) );
       mScaleVisibilityGroupBox->setChecked( settingList.at( 0 ).scaleBasedVisibility );
       mDiagramUnitComboBox->setUnit( settingList.at( 0 ).sizeType );
       mDiagramUnitComboBox->setMapUnitScale( settingList.at( 0 ).sizeScale );
@@ -774,8 +773,8 @@ void QgsDiagramProperties::apply()
   ds.penColor = mDiagramPenColorButton->color();
   ds.penWidth = mPenWidthSpinBox->value();
   // caution: layer uses scale denoms, widget uses true scales
-  ds.maxScaleDenominator = 1.0 / mScaleRangeWidget->minimumScale();
+  ds.maxScaleDenominator = mScaleRangeWidget->minimumScale();
-  ds.minScaleDenominator = 1.0 / mScaleRangeWidget->maximumScale();
+  ds.minScaleDenominator = mScaleRangeWidget->maximumScale();
   ds.scaleBasedVisibility = mScaleVisibilityGroupBox->isChecked();
 
   // Diagram angle offset (pie)

src/app/qgsdxfexportdialog.cpp

@@ -453,7 +453,9 @@ QgsDxfExportDialog::QgsDxfExportDialog( QWidget *parent, Qt::WindowFlags f )
 
   //last symbol scale
   mScaleWidget->setMapCanvas( QgisApp::instance()->mapCanvas() );
-  mScaleWidget->setScale( QgsProject::instance()->readEntry( QStringLiteral( "dxf" ), QStringLiteral( "/lastSymbologyExportScale" ), s.value( QStringLiteral( "qgis/lastSymbologyExportScale" ), "1/50000" ).toString() ).toDouble() );
+  double oldScale = QgsProject::instance()->readEntry( QStringLiteral( "dxf" ), QStringLiteral( "/lastSymbologyExportScale" ), s.value( QStringLiteral( "qgis/lastSymbologyExportScale" ), "1/50000" ).toString() ).toDouble();
+  if ( oldScale != 0.0 )
+    mScaleWidget->setScale( 1.0 / oldScale );
   mLayerTitleAsName->setChecked( QgsProject::instance()->readEntry( QStringLiteral( "dxf" ), QStringLiteral( "/lastDxfLayerTitleAsName" ), s.value( QStringLiteral( "qgis/lastDxfLayerTitleAsName" ), "false" ).toString() ) != QLatin1String( "false" ) );
   mMapExtentCheckBox->setChecked( QgsProject::instance()->readEntry( QStringLiteral( "dxf" ), QStringLiteral( "/lastDxfMapRectangle" ), s.value( QStringLiteral( "qgis/lastDxfMapRectangle" ), "false" ).toString() ) != QLatin1String( "false" ) );
 
@@ -545,10 +547,7 @@ QList< QPair<QgsVectorLayer *, int> > QgsDxfExportDialog::layers() const
 
 double QgsDxfExportDialog::symbologyScale() const
 {
-  if ( qgsDoubleNear( mScaleWidget->scale(), 0.0 ) )
+  double scale = mScaleWidget->scale();
-    return 1.0;
-
-  double scale = 1.0 / mScaleWidget->scale();
   if ( qgsDoubleNear( scale, 0.0 ) )
     return 1.0;
 
@@ -613,14 +612,14 @@ void QgsDxfExportDialog::saveSettings()
   QFileInfo dxfFileInfo( mFileLineEdit->text() );
   s.setValue( QStringLiteral( "qgis/lastDxfDir" ), dxfFileInfo.absolutePath() );
   s.setValue( QStringLiteral( "qgis/lastDxfSymbologyMode" ), mSymbologyModeComboBox->currentIndex() );
-  s.setValue( QStringLiteral( "qgis/lastSymbologyExportScale" ), mScaleWidget->scale() );
+  s.setValue( QStringLiteral( "qgis/lastSymbologyExportScale" ), mScaleWidget->scale() != 0 ? 1.0 / mScaleWidget->scale() : 0 );
   s.setValue( QStringLiteral( "qgis/lastDxfMapRectangle" ), mMapExtentCheckBox->isChecked() );
   s.setValue( QStringLiteral( "qgis/lastDxfLayerTitleAsName" ), mLayerTitleAsName->isChecked() );
   s.setValue( QStringLiteral( "qgis/lastDxfEncoding" ), mEncoding->currentText() );
   s.setValue( QStringLiteral( "qgis/lastDxfCrs" ), QString::number( mCRS.srsid() ) );
 
   QgsProject::instance()->writeEntry( QStringLiteral( "dxf" ), QStringLiteral( "/lastDxfSymbologyMode" ), mSymbologyModeComboBox->currentIndex() );
-  QgsProject::instance()->writeEntry( QStringLiteral( "dxf" ), QStringLiteral( "/lastSymbologyExportScale" ), mScaleWidget->scale() );
+  QgsProject::instance()->writeEntry( QStringLiteral( "dxf" ), QStringLiteral( "/lastSymbologyExportScale" ), mScaleWidget->scale() != 0 ? 1.0 / mScaleWidget->scale() : 0 );
   QgsProject::instance()->writeEntry( QStringLiteral( "dxf" ), QStringLiteral( "/lastDxfLayerTitleAsName" ), mLayerTitleAsName->isChecked() );
   QgsProject::instance()->writeEntry( QStringLiteral( "dxf" ), QStringLiteral( "/lastDxfMapRectangle" ), mMapExtentCheckBox->isChecked() );
   QgsProject::instance()->writeEntry( QStringLiteral( "dxf" ), QStringLiteral( "/lastDxfEncoding" ), mEncoding->currentText() );

src/app/qgsmapcanvasdockwidget.cpp

@@ -133,7 +133,7 @@ QgsMapCanvasDockWidget::QgsMapCanvasDockWidget( const QString &name, QWidget *pa
     if ( !mBlockScaleUpdate )
     {
       mBlockScaleUpdate = true;
-      mMapCanvas->zoomScale( 1.0 / scale );
+      mMapCanvas->zoomScale( scale );
       mBlockScaleUpdate = false;
     }
   } );
@@ -142,7 +142,7 @@ QgsMapCanvasDockWidget::QgsMapCanvasDockWidget( const QString &name, QWidget *pa
     if ( !mBlockScaleUpdate )
     {
       mBlockScaleUpdate = true;
-      mScaleCombo->setScale( 1.0 / scale );
+      mScaleCombo->setScale( scale );
       mBlockScaleUpdate = false;
     }
   } );

src/app/qgsmapsavedialog.cpp

@@ -53,7 +53,7 @@ QgsMapSaveDialog::QgsMapSaveDialog( QWidget *parent, QgsMapCanvas *mapCanvas, co
   mExtentGroupBox->setCurrentExtent( mExtent, ms.destinationCrs() );
   mExtentGroupBox->setOutputExtentFromCurrent();
 
-  mScaleWidget->setScale( 1 / ms.scale() );
+  mScaleWidget->setScale( ms.scale() );
   mScaleWidget->setMapCanvas( mMapCanvas );
   mScaleWidget->setShowCurrentScaleButton( true );
 
@@ -144,7 +144,7 @@ void QgsMapSaveDialog::updateScale( double scale )
   calculator.setDpi( mDpi );
 
   double oldScale = 1 / ( calculator.calculate( mExtent, mSize.width() ) );
-  double scaleRatio = oldScale / scale;
+  double scaleRatio = scale / oldScale;
   mExtent.scale( scaleRatio );
   mExtentGroupBox->setOutputExtentFromUser( mExtent, mExtentGroupBox->currentCrs() );
 }

src/app/qgsoptions.cpp

@@ -602,7 +602,7 @@ QgsOptions::QgsOptions( QWidget *parent, Qt::WindowFlags fl, const QList<QgsOpti
   QStringList myScalesList = PROJECT_SCALES.split( ',' );
   myScalesList.append( QStringLiteral( "1:1" ) );
   mSimplifyMaximumScaleComboBox->updateScales( myScalesList );
-  mSimplifyMaximumScaleComboBox->setScale( 1.0 / mSettings->value( QStringLiteral( "/qgis/simplifyMaxScale" ), 1 ).toFloat() );
+  mSimplifyMaximumScaleComboBox->setScale( mSettings->value( QStringLiteral( "/qgis/simplifyMaxScale" ), 1 ).toFloat() );
 
   // Magnifier
   double magnifierMin = 100 * QgsGuiUtils::CANVAS_MAGNIFICATION_MIN;
@@ -1255,7 +1255,7 @@ void QgsOptions::saveOptions()
   mSettings->setValue( QStringLiteral( "/qgis/simplifyAlgorithm" ), mSimplifyAlgorithmComboBox->currentData().toInt() );
   mSettings->setValue( QStringLiteral( "/qgis/simplifyDrawingTol" ), mSimplifyDrawingSpinBox->value() );
   mSettings->setValue( QStringLiteral( "/qgis/simplifyLocal" ), !mSimplifyDrawingAtProvider->isChecked() );
-  mSettings->setValue( QStringLiteral( "/qgis/simplifyMaxScale" ), 1.0 / mSimplifyMaximumScaleComboBox->scale() );
+  mSettings->setValue( QStringLiteral( "/qgis/simplifyMaxScale" ), mSimplifyMaximumScaleComboBox->scale() );
 
   // magnification
   mSettings->setValue( QStringLiteral( "/qgis/magnifier_factor_default" ), doubleSpinBoxMagnifierDefault->value() / 100 );

src/app/qgsrasterlayerproperties.cpp

@@ -141,7 +141,7 @@ QgsRasterLayerProperties::QgsRasterLayerProperties( QgsMapLayer *lyr, QgsMapCanv
   // set up the scale based layer visibility stuff....
   mScaleRangeWidget->setMapCanvas( mMapCanvas );
   chkUseScaleDependentRendering->setChecked( lyr->hasScaleBasedVisibility() );
-  mScaleRangeWidget->setScaleRange( 1.0 / lyr->minimumScale(), 1.0 / lyr->maximumScale() ); // caution: layer uses scale denoms, widget uses true scales
+  mScaleRangeWidget->setScaleRange( lyr->minimumScale(), lyr->maximumScale() );
 
   leNoDataValue->setValidator( new QDoubleValidator( -std::numeric_limits<double>::max(), std::numeric_limits<double>::max(), 1000, this ) );
 
@@ -910,9 +910,8 @@ void QgsRasterLayerProperties::apply()
 
   // set up the scale based layer visibility stuff....
   mRasterLayer->setScaleBasedVisibility( chkUseScaleDependentRendering->isChecked() );
-  // caution: layer uses scale denoms, widget uses true scales
+  mRasterLayer->setMinimumScale( mScaleRangeWidget->minimumScale() );
-  mRasterLayer->setMinimumScale( 1.0 / mScaleRangeWidget->minimumScale() );
+  mRasterLayer->setMaximumScale( mScaleRangeWidget->maximumScale() );
-  mRasterLayer->setMaximumScale( 1.0 / mScaleRangeWidget->maximumScale() );
 
   mRasterLayer->setAutoRefreshInterval( mRefreshLayerIntervalSpinBox->value() * 1000.0 );
   mRasterLayer->setAutoRefreshEnabled( mRefreshLayerCheckBox->isChecked() );

src/app/qgsrulebasedlabelingwidget.cpp

@@ -602,9 +602,9 @@ QgsLabelingRulePropsWidget::QgsLabelingRulePropsWidget( QgsRuleBasedLabeling::Ru
     groupScale->setChecked( true );
     // caution: rule uses scale denom, scale widget uses true scales
     if ( rule->scaleMinDenom() > 0 )
-      mScaleRangeWidget->setMaximumScale( 1.0 / rule->scaleMinDenom() );
+      mScaleRangeWidget->setMaximumScale( rule->scaleMinDenom() );
     if ( rule->scaleMaxDenom() > 0 )
-      mScaleRangeWidget->setMinimumScale( 1.0 / rule->scaleMaxDenom() );
+      mScaleRangeWidget->setMinimumScale( rule->scaleMaxDenom() );
   }
   mScaleRangeWidget->setMapCanvas( mMapCanvas );
 
@@ -704,7 +704,7 @@ void QgsLabelingRulePropsWidget::apply()
   mRule->setFilterExpression( editFilter->text() );
   mRule->setDescription( editDescription->text() );
   // caution: rule uses scale denom, scale widget uses true scales
-  mRule->setScaleMinDenom( groupScale->isChecked() ? mScaleRangeWidget->minimumScaleDenom() : 0 );
+  mRule->setScaleMinDenom( groupScale->isChecked() ? mScaleRangeWidget->minimumScale() : 0 );
-  mRule->setScaleMaxDenom( groupScale->isChecked() ? mScaleRangeWidget->maximumScaleDenom() : 0 );
+  mRule->setScaleMaxDenom( groupScale->isChecked() ? mScaleRangeWidget->maximumScale() : 0 );
   mRule->setSettings( groupSettings->isChecked() ? new QgsPalLayerSettings( mLabelingGui->layerSettings() ) : nullptr );
 }

src/app/qgsstatusbarscalewidget.cpp

@@ -80,7 +80,7 @@ QgsStatusBarScaleWidget::~QgsStatusBarScaleWidget()
 void QgsStatusBarScaleWidget::setScale( double scale )
 {
   mScale->blockSignals( true );
-  mScale->setScale( scale );
+  mScale->setScale( 1.0 / scale );
   mScale->blockSignals( false );
 }
 
@@ -102,6 +102,5 @@ void QgsStatusBarScaleWidget::updateScales( const QStringList &scales )
 
 void QgsStatusBarScaleWidget::userScale() const
 {
-  // Why has MapCanvas the scale inverted?
+  mMapCanvas->zoomScale( mScale->scale() );
-  mMapCanvas->zoomScale( 1.0 / mScale->scale() );
 }

src/app/qgsvectorlayerproperties.cpp

@@ -411,7 +411,7 @@ void QgsVectorLayerProperties::syncToLayer()
   mDisplayExpressionWidget->setField( mLayer->displayExpression() );
 
   // set up the scale based layer visibility stuff....
-  mScaleRangeWidget->setScaleRange( 1.0 / mLayer->minimumScale(), 1.0 / mLayer->maximumScale() ); // caution: layer uses scale denoms, widget uses true scales
+  mScaleRangeWidget->setScaleRange( mLayer->minimumScale(), mLayer->maximumScale() );
   mScaleVisibilityGroupBox->setChecked( mLayer->hasScaleBasedVisibility() );
   mScaleRangeWidget->setMapCanvas( QgisApp::instance()->mapCanvas() );
 
@@ -456,7 +456,7 @@ void QgsVectorLayerProperties::syncToLayer()
   QStringList myScalesList = PROJECT_SCALES.split( ',' );
   myScalesList.append( QStringLiteral( "1:1" ) );
   mSimplifyMaximumScaleComboBox->updateScales( myScalesList );
-  mSimplifyMaximumScaleComboBox->setScale( 1.0 / simplifyMethod.maximumScale() );
+  mSimplifyMaximumScaleComboBox->setScale( simplifyMethod.maximumScale() );
 
   mForceRasterCheckBox->setChecked( mLayer->renderer() && mLayer->renderer()->forceRasterRender() );
 
@@ -509,9 +509,8 @@ void QgsVectorLayerProperties::apply()
 
   // set up the scale based layer visibility stuff....
   mLayer->setScaleBasedVisibility( mScaleVisibilityGroupBox->isChecked() );
-  // caution: layer uses scale denoms, widget uses true scales
+  mLayer->setMaximumScale( mScaleRangeWidget->maximumScale() );
-  mLayer->setMinimumScale( mScaleRangeWidget->maximumScaleDenom() );
+  mLayer->setMinimumScale( mScaleRangeWidget->minimumScale() );
-  mLayer->setMaximumScale( mScaleRangeWidget->minimumScaleDenom() );
 
   // provider-specific options
   if ( mLayer->dataProvider() )
@@ -634,7 +633,7 @@ void QgsVectorLayerProperties::apply()
   simplifyMethod.setSimplifyAlgorithm( static_cast< QgsVectorSimplifyMethod::SimplifyAlgorithm >( mSimplifyAlgorithmComboBox->currentData().toInt() ) );
   simplifyMethod.setThreshold( mSimplifyDrawingSpinBox->value() );
   simplifyMethod.setForceLocalOptimization( !mSimplifyDrawingAtProvider->isChecked() );
-  simplifyMethod.setMaximumScale( 1.0 / mSimplifyMaximumScaleComboBox->scale() );
+  simplifyMethod.setMaximumScale( mSimplifyMaximumScaleComboBox->scale() );
   mLayer->setSimplifyMethod( simplifyMethod );
 
   if ( mLayer->renderer() )

src/gui/qgsscalecombobox.cpp

@@ -26,8 +26,6 @@
 
 QgsScaleComboBox::QgsScaleComboBox( QWidget *parent )
   : QComboBox( parent )
-  , mScale( 1.0 )
-  , mMinScale( 0.0 )
 {
   updateScales();
 
@@ -71,7 +69,7 @@ void QgsScaleComboBox::updateScales( const QStringList &scales )
     denominator = QLocale::system().toDouble( parts[1], &ok );
     if ( ok )
     {
-      myScalesList[ i ] = toString( 1.0 / denominator );
+      myScalesList[ i ] = toString( denominator );
     }
   }
 
@@ -114,17 +112,17 @@ void QgsScaleComboBox::showPopup()
   view()->setMinimumWidth( view()->sizeHintForColumn( 0 ) );
 }
 
-QString QgsScaleComboBox::scaleString()
+QString QgsScaleComboBox::scaleString() const
 {
   return toString( mScale );
 }
 
-bool QgsScaleComboBox::setScaleString( const QString &scaleTxt )
+bool QgsScaleComboBox::setScaleString( const QString &string )
 {
   bool ok;
-  double newScale = toDouble( scaleTxt, &ok );
+  double newScale = toDouble( string, &ok );
   double oldScale = mScale;
-  if ( newScale < mMinScale && newScale != 0 )
+  if ( newScale > mMinScale && newScale != 0 && mMinScale != 0 )
   {
     newScale = mMinScale;
   }
@@ -167,7 +165,7 @@ void QgsScaleComboBox::fixupScale()
   if ( ok )
   {
     // if a user types scale = 2345, we transform to 1:2345
-    if ( userSetScale && newScale >= 1.0 )
+    if ( userSetScale && newScale < 1.0 && !qgsDoubleNear( newScale, 0.0 ) )
     {
       newScale = 1 / newScale;
     }
@@ -185,13 +183,13 @@ QString QgsScaleComboBox::toString( double scale )
   {
     return QStringLiteral( "0" );
   }
-  else if ( scale > 1 )
+  else if ( scale <= 1 )
   {
-    return QStringLiteral( "%1:1" ).arg( QLocale::system().toString( qRound( scale ) ) );
+    return QStringLiteral( "%1:1" ).arg( QLocale::system().toString( qRound( 1.0 / scale ) ) );
   }
   else
   {
-    return QStringLiteral( "1:%1" ).arg( QLocale::system().toString( qRound( 1.0 / scale ) ) );
+    return QStringLiteral( "1:%1" ).arg( QLocale::system().toString( qRound( scale ) ) );
   }
 }
 
@@ -200,7 +198,8 @@ double QgsScaleComboBox::toDouble( const QString &scaleString, bool *returnOk )
   bool ok = false;
   QString scaleTxt( scaleString );
 
-  double scale = qgsPermissiveToDouble( scaleTxt, ok );
+  double denominator = qgsPermissiveToDouble( scaleTxt, ok );
+  double scale = !qgsDoubleNear( denominator, 0.0 ) ? 1.0 / denominator : 0.0;
   if ( ok )
   {
     // Create a text version and set that text and rescan
@@ -217,10 +216,10 @@ double QgsScaleComboBox::toDouble( const QString &scaleString, bool *returnOk )
       bool okY = false;
       int x = qgsPermissiveToInt( txtList[ 0 ], okX );
       int y = qgsPermissiveToInt( txtList[ 1 ], okY );
-      if ( okX && okY )
+      if ( okX && okY && x != 0 )
       {
         // Scale is fraction of x and y
-        scale = ( double )x / ( double )y;
+        scale = static_cast<  double >( y ) / static_cast< double >( x );
         ok = true;
       }
     }
@@ -237,8 +236,8 @@ double QgsScaleComboBox::toDouble( const QString &scaleString, bool *returnOk )
 void QgsScaleComboBox::setMinScale( double scale )
 {
   mMinScale = scale;
-  if ( mScale < scale && mScale != 0 )
+  if ( mScale > mMinScale && mScale != 0 && mMinScale != 0 )
   {
-    setScale( scale );
+    setScale( mMinScale );
   }
 }

src/gui/qgsscalecombobox.h

@@ -29,38 +29,87 @@
 class GUI_EXPORT QgsScaleComboBox : public QComboBox
 {
     Q_OBJECT
+    Q_PROPERTY( double scale READ scale WRITE setScale NOTIFY scaleChanged )
+    Q_PROPERTY( double minScale READ minScale WRITE setMinScale )
+
   public:
+
+    /**
+     * Constructor for QgsScaleComboBox.
+     */
     QgsScaleComboBox( QWidget *parent SIP_TRANSFERTHIS = nullptr );
 
-    //! Function to read the selected scale as text
+    /**
-    QString scaleString();
+     * Returns the selected scale as a string, e.g. "1:150".
-    //! Function to set the selected scale from text
+     * \see setScaleString()
-    bool setScaleString( const QString &scaleTxt );
+     */
-    //! Function to read the selected scale as double
+    QString scaleString() const;
+
+    /**
+     * Set the selected scale from a \a string, e.g. "1:150".
+     * \see scaleString()
+     */
+    bool setScaleString( const QString &string );
+
+    /**
+     * Returns the selected scale as a double.
+     * The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * \see setScale()
+     */
     double scale() const;
-    //! Function to set the selected scale from double
+
-    void setScale( double scale );
+    /**
-    //! Function to read the min scale
+     * Returns the minimum scale, or 0 if no minimum scale set.
+     * The \a scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * Any scale lower than the minimum scale will automatically be converted to the minimum scale.
+     * Except for 0 which is always allowed.
+     */
     double minScale() const { return mMinScale; }
 
-    //! Helper function to convert a double to scale string
+    /**
-    // Performs rounding, so an exact representation is not to
+     * Helper function to convert a \a scale double to scale string.
-    // be expected.
+     * The \a scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     *
+     * The returned string will be rounded (e.g. 1:1000, not 1:1000.345).
+     * \see toDouble()
+     */
     static QString toString( double scale );
-    //! Helper function to convert a scale string to double
+
-    static double toDouble( const QString &scaleString, bool *ok = nullptr );
+    /**
+     * Helper function to convert a scale \a string to double.
+     * The returned value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * If specified, \a ok will be set to true if the string was successfully interpreted as a scale.
+     * \see toString()
+     */
+    static double toDouble( const QString &string, bool *ok = nullptr );
 
   signals:
-    //! Signal is emitted when *user* has finished editing/selecting a new scale.
+
+    /**
+     * Emitted when *user* has finished editing/selecting a new scale.
+     * The \a scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     */
     void scaleChanged( double scale );
 
   public slots:
+
+    /**
+     * Sets the list of predefined \a scales to show in the combobox. List elements
+     * are expected to be valid scale strings, such as "1:1000000".
+     */
     void updateScales( const QStringList &scales = QStringList() );
 
     /**
-     * Set the minimum allowed scale.
+     * Set the selected scale from a double.
-     * Anything scale lower than the minimum scale will automatically
+     * The \a scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
-     * be converted to the minimum scale.
+     * \see scale()
+     */
+    void setScale( double scale );
+
+    /**
+     * Set the minimum allowed \a scale. Set to 0 to disable the minimum scale.
+     * The \a scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * Any scale lower than the minimum scale will automatically be converted to the minimum scale.
      * Except for 0 which is always allowed.
      */
     void setMinScale( double scale );
@@ -72,8 +121,8 @@ class GUI_EXPORT QgsScaleComboBox : public QComboBox
     void fixupScale();
 
   private:
-    double mScale;
+    double mScale = 1.0;
-    double mMinScale;
+    double mMinScale = 0.0;
 };
 
 #endif // QGSSCALECOMBOBOX_H

src/gui/qgsscalerangewidget.cpp

@@ -48,8 +48,8 @@ QgsScaleRangeWidget::QgsScaleRangeWidget( QWidget *parent )
   mMaximumScaleWidget->setShowCurrentScaleButton( true );
   reloadProjectScales();
   // add start, add comprehension of scales by settings fake ordered values
-  mMinimumScaleWidget->setScale( 1.0 / 100000 );
+  mMinimumScaleWidget->setScale( 100000 );
-  mMaximumScaleWidget->setScale( 1.0 / 1000 );
+  mMaximumScaleWidget->setScale( 1000 );
 
   mLayout->addWidget( minLbl, 0, 0, 1, 2 );
   mLayout->addWidget( mMinimumScaleIconLabel, 1, 0 );
@@ -86,46 +86,24 @@ void QgsScaleRangeWidget::setMapCanvas( QgsMapCanvas *mapCanvas )
 
 void QgsScaleRangeWidget::setMinimumScale( double scale )
 {
-  if ( qIsInf( scale ) )
-    scale = 0;
   mMinimumScaleWidget->setScale( scale );
 }
 
-double QgsScaleRangeWidget::minimumScale()
+double QgsScaleRangeWidget::minimumScale() const
 {
   return mMinimumScaleWidget->scale();
 }
 
 void QgsScaleRangeWidget::setMaximumScale( double scale )
 {
-  if ( qIsInf( scale ) )
-    scale = 0;
   mMaximumScaleWidget->setScale( scale );
 }
 
-double QgsScaleRangeWidget::maximumScale()
+double QgsScaleRangeWidget::maximumScale() const
 {
   return mMaximumScaleWidget->scale();
 }
 
-double QgsScaleRangeWidget::minimumScaleDenom()
-{
-  double scale = maximumScale();
-  if ( scale == 0 )
-    return 0;
-  else
-    return qRound( 1.0 / scale );
-}
-
-double QgsScaleRangeWidget::maximumScaleDenom()
-{
-  double scale = minimumScale();
-  if ( scale == 0 )
-    return 0;
-  else
-    return qRound( 1.0 / scale );
-}
-
 void QgsScaleRangeWidget::setScaleRange( double min, double max )
 {
   setMinimumScale( min );

src/gui/qgsscalerangewidget.h

@@ -24,64 +24,86 @@
 class QgsMapCanvas;
 class QgsScaleWidget;
 
-/** \ingroup gui
+/**
+ * \ingroup gui
  * \class QgsScaleRangeWidget
+ * A widget allowing entry of a range of map scales, e.g. minimum scale and maximum scale.
  */
 class GUI_EXPORT QgsScaleRangeWidget : public QWidget
 {
     Q_OBJECT
+    Q_PROPERTY( double minimumScale READ minimumScale WRITE setMinimumScale )
+    Q_PROPERTY( double maximumScale READ maximumScale WRITE setMaximumScale )
 
   public:
+
+    /**
+     * Constructor for QgsScaleRangeWidget.
+     */
     explicit QgsScaleRangeWidget( QWidget *parent SIP_TRANSFERTHIS = 0 );
 
-    //! set the map canvas which will be used for the current scale buttons
+    /**
+     * Sets the map \a canvas which will be used for the current scale buttons.
+     * If not set, the buttons are hidden.
+     */
+    void setMapCanvas( QgsMapCanvas *canvas );
 
     /**
-     * \brief setMapCanvas set the map canvas which will be used for the current scale buttons
+     * Returns the selected minimum scale, or 0 if minimum scale is not set.
-     * if not set, the buttons are hidden.
+     * The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * \see maximumScale()
+     * \see setMinimumScale()
      */
-    void setMapCanvas( QgsMapCanvas *mapCanvas );
+    double minimumScale() const;
-
-    //! return the minimum scale
-    double minimumScale();
-
-    //! return the maximum scale
-    double maximumScale();
 
     /**
-     * Returns the minimum scale denominator ( = 1 / maximum scale )
+     * Returns the selected maximum scale, or 0 if maximum scale is not set.
-     * In case of maximum scale = 0 it will also return 0
+     * The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * \see minimumScale()
+     * \see setMaximumScale()
      */
-    double minimumScaleDenom();
+    double maximumScale() const;
 
     /**
-     * Returns the maximum scale denominator ( = 1 / minimum scale )
+     * Call to reload the preset scales from the current project and apply them to the 2 scales combo boxes.
-     * In case of minimum scale = 0 it will also return 0
      */
-    double maximumScaleDenom();
-
-    //! call to reload the project scales and apply them to the 2 scales combo boxes
     void reloadProjectScales();
 
   public slots:
 
     /**
-     * Set the minimum scale. Infinite will be handled equally to 0 internally.
+     * Set the minimum \a scale, or 0 to indicate the minimum is not set.
+     * The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * \see minimumScale()
+     * \see setMaximumScale()
+     * \see setScaleRange()
      */
     void setMinimumScale( double scale );
 
     /**
-     * Set the maximum scale. Infinite will be handled equally to 0 internally.
+     * Set the maximum \a scale, or 0 to indicate the minimum is not set.
+     * The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * \see maximumScale()
+     * \see setMinimumScale()
+     * \see setScaleRange()
      */
     void setMaximumScale( double scale );
 
+    /**
+     * Sets the scale range, from \a min scale to \a max scale.
+     * The scale values indicates the scale denominator, e.g. 1000.0 for a 1:1000 map,
+     * or 0 to indicate not set.
+     * \see setMinimumScale()
+     * \see setMaximumScale()
+     */
     void setScaleRange( double min, double max );
 
   signals:
 
-    /** Emitted when the scale range set in the widget is changed.
+    /**
-     * \param min minimum scale
+     * Emitted when the scale range set in the widget is changed.
-     * \param max maximum scale
+     * The scale values indicates the scale denominator, e.g. 1000.0 for a 1:1000 map,
+     * or 0 to indicate not set.
      * \since QGIS 2.16
      */
     void rangeChanged( double min, double max );

src/gui/qgsscalevisibilitydialog.cpp

@@ -59,7 +59,7 @@ void QgsScaleVisibilityDialog::setScaleVisiblity( bool hasScaleVisibility )
   mGroupBox->setChecked( hasScaleVisibility );
 }
 
-bool QgsScaleVisibilityDialog::hasScaleVisibility()
+bool QgsScaleVisibilityDialog::hasScaleVisibility() const
 {
   return mGroupBox->isChecked();
 }
@@ -69,7 +69,7 @@ void QgsScaleVisibilityDialog::setMinimumScale( double minScale )
   mScaleWidget->setMinimumScale( minScale );
 }
 
-double QgsScaleVisibilityDialog::minimumScale()
+double QgsScaleVisibilityDialog::minimumScale() const
 {
   return mScaleWidget->minimumScale();
 }
@@ -79,7 +79,7 @@ void QgsScaleVisibilityDialog::setMaximumScale( double maxScale )
   mScaleWidget->setMaximumScale( maxScale );
 }
 
-double QgsScaleVisibilityDialog::maximumScale()
+double QgsScaleVisibilityDialog::maximumScale() const
 {
   return mScaleWidget->maximumScale();
 }

src/gui/qgsscalevisibilitydialog.h

@@ -26,33 +26,68 @@ class QgsScaleRangeWidget;
 
 /** \ingroup gui
  * \class QgsScaleVisibilityDialog
+ * A dialog allowing users to enter a scale visibility range.
  */
 class GUI_EXPORT QgsScaleVisibilityDialog : public QDialog
 {
     Q_OBJECT
+    Q_PROPERTY( bool hasScaleVisibility READ hasScaleVisibility WRITE setScaleVisiblity )
+    Q_PROPERTY( double minimumScale READ minimumScale WRITE setMinimumScale )
+    Q_PROPERTY( double maximumScale READ maximumScale WRITE setMaximumScale )
 
   public:
+
+    /**
+     * Constructor for QgsScaleVisibilityDialog, with specified dialog \a title. The \a mapCanvas argument
+     * can be used to associate the dialog with a map canvas, allowing use of the current map scale
+     * within the dialog.
+     */
     explicit QgsScaleVisibilityDialog( QWidget *parent SIP_TRANSFERTHIS = 0, const QString &title = QString(), QgsMapCanvas *mapCanvas = nullptr );
 
-    //! return if scale visibilty is enabled
+    /**
-    bool hasScaleVisibility();
+     * Return true if scale based visibilty is enabled.
+     */
+    bool hasScaleVisibility() const;
 
-    //! return minimum scale (true scale, not scale denominator)
+    /**
-    double minimumScale();
+     * Returns the selected minimum scale, or 0 if minimum scale is not set.
-
+     * The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
-    //! return maximum scale (true scale, not scale denominator)
+     * \see maximumScale()
-    double maximumScale();
+     * \see setMinimumScale()
+     */
+    double minimumScale() const;
 
+    /**
+     * Returns the selected maximum scale, or 0 if maximum scale is not set.
+     * The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * \see minimumScale()
+     * \see setMaximumScale())
+     */
+    double maximumScale() const;
 
   public slots:
-    //! set if scale visibility is enabled
+
+    /**
+     * Set whether scale based visibility is enabled.
+     * \see hasScaleVisibility()
+     */
     void setScaleVisiblity( bool hasScaleVisibility );
 
-    //! set minimum scale (true scale, not scale denominator)
+    /**
-    void setMinimumScale( double minScale );
+     * Set the minimum \a scale, or 0 to indicate the minimum is not set.
+     * The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * \see minimumScale()
+     * \see setMaximumScale()
+     */
+    void setMinimumScale( double scale );
 
-    //! set maximum scale (true scale, not scale denominator)
+    /**
-    void setMaximumScale( double maxScale );
+     * Set the maximum \a scale, or 0 to indicate the minimum is not set.
+     * The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * \see maximumScale()
+     * \see setMinimumScale()
+     */
+    void setMaximumScale( double scale );
 
 
   private:

src/gui/qgsscalewidget.cpp

@@ -58,7 +58,7 @@ void QgsScaleWidget::setScaleFromCanvas()
   if ( !mCanvas )
     return;
 
-  setScale( 1 / mCanvas->scale() );
+  setScale( mCanvas->scale() );
 }
 
 void QgsScaleWidget::setScale( double scale )

src/gui/qgsscalewidget.h

@@ -45,45 +45,104 @@ class GUI_EXPORT QgsScaleWidget : public QWidget
      **/
     explicit QgsScaleWidget( QWidget *parent SIP_TRANSFERTHIS = nullptr );
 
-    //! shows a button to set the scale to the current scale of the map canvas next to the combobox
+    /**
-    //! \note the map canvas must be defined to show the button
+     * Sets whether to show a button to set the scale to the current scale of the map canvas next to the combobox.
+     * \note the map canvas must be defined to show the button
+     * \see showCurrentScaleButton()
+     * \see setMapCanvas()
+     */
     void setShowCurrentScaleButton( bool showCurrentScaleButton );
-    //! returns if a button to set the scale from map canvas is shown or not
+
+    /**
+     * Returns whether a button to set the scale from map canvas is shown or not.
+     * \see setShowCurrentScaleButton()
+     */
     bool showCurrentScaleButton() { return mShowCurrentScaleButton;}
 
-    //! set the map canvas associated to the current button
+    /**
+     * Set the map \a canvas associated to the current button.
+     */
     void setMapCanvas( QgsMapCanvas *canvas );
 
-    //! Function to read the selected scale as text
+    /**
-    QString scaleString() { return mScaleComboBox->scaleString(); }
+     * Returns the selected scale as a string, e.g. "1:150".
-    //! Function to set the selected scale from text
+     * \see setScaleString()
-    bool setScaleString( const QString &scaleTxt ) { return mScaleComboBox->setScaleString( scaleTxt ); }
+     */
-    //! Function to read the selected scale as double
+    QString scaleString() const { return mScaleComboBox->scaleString(); }
-    double scale() const { return mScaleComboBox->scale();}
+
-    //! Function to set the selected scale from double
+    /**
-    void setScale( double scale );
+     * Set the selected scale from a \a string, e.g. "1:150".
-    //! Function to read the min scale
+     * \see scaleString()
+     */
+    bool setScaleString( const QString &string ) { return mScaleComboBox->setScaleString( string ); }
+
+    /**
+     * Returns the selected scale as a double.
+     * The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * \see setScale()
+     */
+    double scale() const { return mScaleComboBox->scale(); }
+
+    /**
+     * Returns the minimum scale, or 0 if no minimum scale set.
+     * The \a scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * Any scale lower than the minimum scale will automatically be converted to the minimum scale.
+     * Except for 0 which is always allowed.
+     */
     double minScale() const { return mScaleComboBox->minScale(); }
 
-    //! Helper function to convert a double to scale string
+    /**
-    // Performs rounding, so an exact representation is not to
+     * Helper function to convert a \a scale double to scale string.
-    // be expected.
+     * The \a scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     *
+     * The returned string will be rounded (e.g. 1:1000, not 1:1000.345).
+     * \see toDouble()
+     */
     static QString toString( double scale ) { return QgsScaleComboBox::toString( scale ); }
-    //! Helper function to convert a scale string to double
+
+    /**
+     * Helper function to convert a scale \a string to double.
+     * The returned value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * If specified, \a ok will be set to true if the string was successfully interpreted as a scale.
+     * \see toString()
+     */
     static double toDouble( const QString &scaleString, bool *ok = nullptr ) { return QgsScaleComboBox::toDouble( scaleString, ok ); }
 
   public slots:
-    //! updates the list of predefined scales
+
+    /**
+     * Set the selected scale from a double.
+     * The \a scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * \see scale()
+     */
+    void setScale( double scale );
+
+    /**
+     * Sets the list of predefined \a scales to show in the combobox. List elements
+     * are expected to be valid scale strings, such as "1:1000000".
+     */
     void updateScales( const QStringList &scales = QStringList() ) { return mScaleComboBox->updateScales( scales ); }
 
-    //! assign the current scale from the map canvas
+    /**
+     * Assigns the current scale from the map canvas, if set.
+     * \see setMapCanvas()
+     */
     void setScaleFromCanvas();
 
-    //! Function to set the min scale
+    /**
+     * Set the minimum allowed \a scale. Set to 0 to disable the minimum scale.
+     * The \a scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     * Any scale lower than the minimum scale will automatically be converted to the minimum scale.
+     * Except for 0 which is always allowed.
+     */
     void setMinScale( double scale ) { mScaleComboBox->setMinScale( scale ); }
 
   signals:
-    //! Signal is emitted when *user* has finished editing/selecting a new scale.
+
+    /**
+     * Emitted when *user* has finished editing/selecting a new scale.
+     * The \a scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.
+     */
     void scaleChanged( double scale );
 
   private:

src/gui/qgstextformatwidget.cpp

@@ -482,7 +482,7 @@ void QgsTextFormatWidget::initWidget()
   if ( mMapCanvas )
   {
     lblFontPreview->setMapUnits( mMapCanvas->mapSettings().mapUnits() );
-    mPreviewScaleComboBox->setScale( 1.0 / mMapCanvas->mapSettings().scale() );
+    mPreviewScaleComboBox->setScale( mMapCanvas->mapSettings().scale() );
   }
 }
 
@@ -1227,7 +1227,7 @@ void QgsTextFormatWidget::onSubstitutionsChanged( const QgsStringReplacementColl
 
 void QgsTextFormatWidget::previewScaleChanged( double scale )
 {
-  lblFontPreview->setScale( scale );
+  lblFontPreview->setScale( 1.0 / scale );
 }
 
 void QgsTextFormatWidget::updateSvgWidgets( const QString &svgPath )

src/gui/qgsunitselectionwidget.cpp

@@ -24,7 +24,7 @@ QgsMapUnitScaleWidget::QgsMapUnitScaleWidget( QWidget *parent )
   , mBlockSignals( true )
 {
   setupUi( this );
-  mComboBoxMinScale->setScale( 0.0000001 );
+  mComboBoxMinScale->setScale( 10000000.0 );
   mComboBoxMaxScale->setScale( 1 );
   mSpinBoxMinSize->setShowClearButton( false );
   mSpinBoxMaxSize->setShowClearButton( false );
@@ -54,10 +54,10 @@ void QgsMapUnitScaleWidget::setMapUnitScale( const QgsMapUnitScale &scale )
   // can't block signals on the widgets themselves, some use them to update
   // internal states
   mBlockSignals = true;
-  mComboBoxMinScale->setScale( scale.minScale > 0.0 ? scale.minScale : 0.0000001 );
+  mComboBoxMinScale->setScale( 1.0 / ( scale.minScale > 0.0 ? scale.minScale : 0.0000001 ) );
   mCheckBoxMinScale->setChecked( scale.minScale > 0.0 );
   mComboBoxMinScale->setEnabled( scale.minScale > 0.0 );
-  mComboBoxMaxScale->setScale( scale.maxScale > 0.0 ? scale.maxScale : 1.0 );
+  mComboBoxMaxScale->setScale( 1.0 / ( scale.maxScale > 0.0 ? scale.maxScale : 1.0 ) );
   mCheckBoxMaxScale->setChecked( scale.maxScale > 0.0 );
   mComboBoxMaxScale->setEnabled( scale.maxScale > 0.0 );
 
@@ -84,7 +84,7 @@ void QgsMapUnitScaleWidget::setMapCanvas( QgsMapCanvas *canvas )
 void QgsMapUnitScaleWidget::configureMinComboBox()
 {
   mComboBoxMinScale->setEnabled( mCheckBoxMinScale->isChecked() );
-  if ( mCheckBoxMinScale->isChecked() && mComboBoxMinScale->scale() > mComboBoxMaxScale->scale() )
+  if ( mCheckBoxMinScale->isChecked() && mComboBoxMinScale->scale() < mComboBoxMaxScale->scale() )
   {
     mComboBoxMinScale->setScale( mComboBoxMaxScale->scale() );
   }
@@ -93,7 +93,7 @@ void QgsMapUnitScaleWidget::configureMinComboBox()
 void QgsMapUnitScaleWidget::configureMaxComboBox()
 {
   mComboBoxMaxScale->setEnabled( mCheckBoxMaxScale->isChecked() );
-  if ( mCheckBoxMaxScale->isChecked() && mComboBoxMaxScale->scale() < mComboBoxMinScale->scale() )
+  if ( mCheckBoxMaxScale->isChecked() && mComboBoxMaxScale->scale() > mComboBoxMinScale->scale() )
   {
     mComboBoxMaxScale->setScale( mComboBoxMinScale->scale() );
   }
@@ -110,8 +110,8 @@ void QgsMapUnitScaleWidget::settingsChanged()
 QgsMapUnitScale QgsMapUnitScaleWidget::mapUnitScale() const
 {
   QgsMapUnitScale scale;
-  scale.minScale = mCheckBoxMinScale->isChecked() ? mComboBoxMinScale->scale() : 0;
+  scale.minScale = mCheckBoxMinScale->isChecked() ? 1.0 / mComboBoxMinScale->scale() : 0;
-  scale.maxScale = mCheckBoxMaxScale->isChecked() ? mComboBoxMaxScale->scale() : 0;
+  scale.maxScale = mCheckBoxMaxScale->isChecked() ? 1.0 / mComboBoxMaxScale->scale() : 0;
   scale.minSizeMMEnabled = mCheckBoxMinSize->isChecked();
   scale.minSizeMM = mSpinBoxMinSize->value();
   scale.maxSizeMMEnabled = mCheckBoxMaxSize->isChecked();

src/gui/symbology-ng/qgsrulebasedrendererwidget.cpp

@@ -623,9 +623,9 @@ QgsRendererRulePropsWidget::QgsRendererRulePropsWidget( QgsRuleBasedRenderer::Ru
     groupScale->setChecked( true );
     // caution: rule uses scale denom, scale widget uses true scales
     if ( rule->scaleMinDenom() > 0 )
-      mScaleRangeWidget->setMaximumScale( 1.0 / rule->scaleMinDenom() );
+      mScaleRangeWidget->setMaximumScale( rule->scaleMinDenom() );
     if ( rule->scaleMaxDenom() > 0 )
-      mScaleRangeWidget->setMinimumScale( 1.0 / rule->scaleMaxDenom() );
+      mScaleRangeWidget->setMinimumScale( rule->scaleMaxDenom() );
   }
   mScaleRangeWidget->setMapCanvas( mContext.mapCanvas() );
 
@@ -770,8 +770,8 @@ void QgsRendererRulePropsWidget::apply()
   mRule->setLabel( editLabel->text() );
   mRule->setDescription( editDescription->text() );
   // caution: rule uses scale denom, scale widget uses true scales
-  mRule->setScaleMinDenom( groupScale->isChecked() ? mScaleRangeWidget->minimumScaleDenom() : 0 );
+  mRule->setScaleMinDenom( groupScale->isChecked() ? mScaleRangeWidget->minimumScale() : 0 );
-  mRule->setScaleMaxDenom( groupScale->isChecked() ? mScaleRangeWidget->maximumScaleDenom() : 0 );
+  mRule->setScaleMaxDenom( groupScale->isChecked() ? mScaleRangeWidget->maximumScale() : 0 );
   mRule->setSymbol( groupSymbol->isChecked() ? mSymbol->clone() : nullptr );
 }
 

tests/src/gui/testqgsscalecombobox.cpp

@@ -40,6 +40,9 @@ class TestQgsScaleComboBox : public QObject
     void basic();
     void slot_test();
     void min_test();
+    void toString();
+    void toDouble();
+
   private:
     void enterScale( const QString &scale );
     void enterScale( double scale );
@@ -70,23 +73,23 @@ void TestQgsScaleComboBox::basic()
   // Testing conversion from "1:nnn".
   enterScale( QStringLiteral( "1:2345" ) );
   QCOMPARE( s->scaleString(), QString( "1:%1" ).arg( QLocale::system().toString( 2345 ) ) );
-  QCOMPARE( s->scale(), 1.0 / 2345.0 );
+  QCOMPARE( s->scale(), 2345.0 );
 
   // Testing conversion from number to "1:x"
   enterScale( 0.02 );
   QCOMPARE( s->scaleString(), QString( "1:%1" ).arg( QLocale::system().toString( 50 ) ) );
-  QCOMPARE( s->scale(), 0.02 );
+  QCOMPARE( s->scale(), 1.0 / 0.02 );
 
   // Testing conversion from number to "1:x"
   enterScale( 42 );
   QCOMPARE( s->scaleString(), QString( "1:%1" ).arg( QLocale::system().toString( 42 ) ) );
-  QCOMPARE( s->scale(), 1.0 / 42.0 );
+  QCOMPARE( s->scale(), 42.0 );
 
   // Testing conversion from number to "1:x,000"
   QString str = QStringLiteral( "1%01000%01000" ).arg( QLocale::system().groupSeparator() );
   enterScale( str );
   QCOMPARE( s->scaleString(), QString( "1:%1" ).arg( str ) );
-  QCOMPARE( s->scale(), 1.0 / 1000000.0 );
+  QCOMPARE( s->scale(), 1000000.0 );
 
   // Testing conversion from number to "1:x,000" with wonky separators
   //(e.g., four digits between thousands, which should be fixed automatically)
@@ -94,7 +97,7 @@ void TestQgsScaleComboBox::basic()
   QString fixedStr = QStringLiteral( "10%01000%01000" ).arg( QLocale::system().groupSeparator() );
   enterScale( str );
   QCOMPARE( s->scaleString(), QString( "1:%1" ).arg( fixedStr ) );
-  QCOMPARE( s->scale(), 1.0 / 10000000.0 );
+  QCOMPARE( s->scale(), 10000000.0 );
 
   // Testing rounding and conversion from illegal
 
@@ -102,22 +105,22 @@ void TestQgsScaleComboBox::basic()
 
   enterScale( QStringLiteral( "1:x:2" ) );
   QCOMPARE( s->scaleString(), QString( "1:%1" ).arg( QLocale::system().toString( 4 ) ) );
-  QCOMPARE( s->scale(), 0.25 );
+  QCOMPARE( s->scale(), 4.0 );
 
   // Test setting programmatically
-  s->setScale( 0.19 );
+  s->setScale( 1.0 / 0.19 );
   QCOMPARE( s->scaleString(), QString( "1:%1" ).arg( QLocale::system().toString( 5 ) ) );
-  QCOMPARE( s->scale(), 0.2 );
+  QCOMPARE( s->scale(), 5.0 );
 
   // Test setting programmatically
   s->setScaleString( QStringLiteral( "1:240" ) );
   QCOMPARE( s->scaleString(), QString( "1:%1" ).arg( QLocale::system().toString( 240 ) ) );
-  QCOMPARE( s->scale(), 1.0 / 240.0 );
+  QCOMPARE( s->scale(), 240.0 );
 
   // Test setting programmatically illegal string
   s->setScaleString( QStringLiteral( "1:2" ) + QLocale::system().decimalPoint() + "4" );
   QCOMPARE( s->scaleString(), QString( "1:%1" ).arg( QLocale::system().toString( 240 ) ) );
-  QCOMPARE( s->scale(), 1.0 / 240.0 );
+  QCOMPARE( s->scale(), 240.0 );
 
 }
 
@@ -135,19 +138,54 @@ void TestQgsScaleComboBox::slot_test()
 
 void TestQgsScaleComboBox::min_test()
 {
-  s->setMinScale( 0.01 );
+  s->setMinScale( 100.0 );
 
   enterScale( 0.02 );
-  QCOMPARE( s->scale(), 0.02 );
+  QCOMPARE( s->scale(), 1.0 / 0.02 );
 
   enterScale( 0.002 );
-  QCOMPARE( s->scale(), 0.01 );
+  QCOMPARE( s->scale(), 100.0 );
 
-  s->setMinScale( 0.015 );
+  s->setMinScale( 1.0 / 0.015 );
-  QCOMPARE( s->scale(), 0.015 );
+  QCOMPARE( s->scale(), 1.0 / 0.015 );
 
-  s->setScale( 0.5 );
+  s->setScale( 2.0 );
-  QCOMPARE( s->scale(), 0.5 );
+  QCOMPARE( s->scale(), 2.0 );
+}
+
+void TestQgsScaleComboBox::toString()
+{
+  QCOMPARE( QgsScaleComboBox::toString( 100 ), QStringLiteral( "1:100" ) );
+  QCOMPARE( QgsScaleComboBox::toString( 100.02134234 ), QStringLiteral( "1:100" ) );
+  QCOMPARE( QgsScaleComboBox::toString( 1 ), QStringLiteral( "1:1" ) );
+  QCOMPARE( QgsScaleComboBox::toString( 1.0 / 100 ), QStringLiteral( "100:1" ) );
+}
+
+void TestQgsScaleComboBox::toDouble()
+{
+  bool ok = false;
+  QCOMPARE( QgsScaleComboBox::toDouble( QStringLiteral( "1:100" ), &ok ), 100.0 );
+  QVERIFY( ok );
+  QCOMPARE( QgsScaleComboBox::toDouble( QStringLiteral( "1:1" ), &ok ), 1.0 );
+  QVERIFY( ok );
+  QCOMPARE( QgsScaleComboBox::toDouble( QStringLiteral( "100:1" ), &ok ), 1.0 / 100 );
+  QVERIFY( ok );
+  QCOMPARE( QgsScaleComboBox::toDouble( QStringLiteral( "0.01" ), &ok ), 100.0 );
+  QVERIFY( ok );
+  QCOMPARE( QgsScaleComboBox::toDouble( QStringLiteral( "100" ), &ok ), 1.0 / 100.0 );
+  QVERIFY( ok );
+
+  //bad
+  QgsScaleComboBox::toDouble( QStringLiteral( "abc" ), &ok );
+  QVERIFY( !ok );
+  QgsScaleComboBox::toDouble( QStringLiteral( "" ), &ok );
+  QVERIFY( !ok );
+  QgsScaleComboBox::toDouble( QStringLiteral( "1:" ), &ok );
+  QVERIFY( !ok );
+  QgsScaleComboBox::toDouble( QStringLiteral( "1:a" ), &ok );
+  QVERIFY( !ok );
+  QgsScaleComboBox::toDouble( QStringLiteral( "a:1" ), &ok );
+  QVERIFY( !ok );
 }
 
 void TestQgsScaleComboBox::enterScale( const QString &scale )