Add mode to QgsScaleComboBox for non-unit ratios

This allows the widget to be used for other scales (or ratios),
not just map scales.

Eg. it allows it to be used for entry of scale ratios like "2:3",
"16:9" etc.

Author: nyalldawson

python/PyQt6/gui/auto_additions/qgsscalecombobox.py

@@ -1,9 +1,22 @@
 # The following has been generated automatically from src/gui/qgsscalecombobox.h
+# monkey patching scoped based enum
+QgsScaleComboBox.RatioMode.ForceUnitNumerator.__doc__ = "Default mode, forces the scale numerator to be 1, e.g. \"1:1000\""
+QgsScaleComboBox.RatioMode.Flexible.__doc__ = "Allows numerator values other than 1, e.g: \"2:3\"."
+QgsScaleComboBox.RatioMode.__doc__ = """Scale ratio modes.
+
+.. versionadded:: 4.0
+
+* ``ForceUnitNumerator``: Default mode, forces the scale numerator to be 1, e.g. \"1:1000\"
+* ``Flexible``: Allows numerator values other than 1, e.g: \"2:3\".
+
+"""
+# --
+QgsScaleComboBox.RatioMode.baseClass = QgsScaleComboBox
 try:
-    QgsScaleComboBox.__attribute_docs__ = {'scaleChanged': 'Emitted when *user* has finished editing/selecting a new scale. The\n``scale`` value indicates the scale denominator, e.g. 1000.0 for a\n1:1000 map.\n'}
+    QgsScaleComboBox.__attribute_docs__ = {'scaleChanged': 'Emitted when *user* has finished editing/selecting a new scale. The\n``scale`` value indicates the scale denominator, e.g. 1000.0 for a\n1:1000 map.\n', 'ratioModeChanged': 'Emitted when the ratio mode for the widget is changed.\n\n.. versionadded:: 4.0\n'}
     QgsScaleComboBox.toString = staticmethod(QgsScaleComboBox.toString)
     QgsScaleComboBox.toDouble = staticmethod(QgsScaleComboBox.toDouble)
     QgsScaleComboBox.__overridden_methods__ = ['showPopup']
-    QgsScaleComboBox.__signal_arguments__ = {'scaleChanged': ['scale: float']}
+    QgsScaleComboBox.__signal_arguments__ = {'scaleChanged': ['scale: float'], 'ratioModeChanged': ['mode: QgsScaleComboBox.RatioMode']}
 except (NameError, AttributeError):
     pass

python/PyQt6/gui/auto_generated/qgsscalecombobox.sip.in

@@ -20,6 +20,12 @@ highlights nearest to current scale value.
 #include "qgsscalecombobox.h"
 %End
   public:
+    enum class RatioMode /BaseType=IntEnum/
+    {
+      ForceUnitNumerator,
+      Flexible,
+    };
+
     QgsScaleComboBox( QWidget *parent /TransferThis/ = 0 );
 %Docstring
 Constructor for QgsScaleComboBox.
@@ -66,14 +72,16 @@ scale lower than the minimum scale will automatically be converted to
 the minimum scale. Except for 0 which is always allowed.
 %End
 
-    static QString toString( double scale );
+    static QString toString( double scale, QgsScaleComboBox::RatioMode mode = QgsScaleComboBox::RatioMode::ForceUnitNumerator );
 %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.
+Helper function to convert a ``scale`` double to scale string.
 
 The returned string will be rounded (e.g. 1:1000, not 1:1000.345).
 
+:param scale: scale value indicating the scale denominator, e.g. 1000.0
+              for a 1:1000 map.
+:param mode: ratio mode (since QGIS 4.0)
+
 .. seealso:: :py:func:`toDouble`
 %End
 
@@ -123,6 +131,15 @@ If ``scales`` is empty then the default user scale options will be used
 instead.
 
 .. versionadded:: 3.38
+%End
+
+    QgsScaleComboBox::RatioMode ratioMode() const;
+%Docstring
+Returns the ratio mode for the scale.
+
+.. seealso:: :py:func:`setRatioMode`
+
+.. versionadded:: 4.0
 %End
 
   signals:
@@ -132,6 +149,13 @@ instead.
 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
+
+    void ratioModeChanged( QgsScaleComboBox::RatioMode mode );
+%Docstring
+Emitted when the ratio mode for the widget is changed.
+
+.. versionadded:: 4.0
 %End
 
   public slots:
@@ -171,6 +195,15 @@ This only has an effect if :py:func:`~QgsScaleComboBox.allowNull` is
 .. seealso:: :py:func:`isNull`
 
 .. versionadded:: 3.8
+%End
+
+    void setRatioMode( QgsScaleComboBox::RatioMode mode );
+%Docstring
+Sets the ratio ``mode`` for the scale.
+
+.. seealso:: :py:func:`ratioMode`
+
+.. versionadded:: 4.0
 %End
 
   protected:

python/gui/auto_additions/qgsscalecombobox.py

@@ -1,9 +1,22 @@
 # The following has been generated automatically from src/gui/qgsscalecombobox.h
+# monkey patching scoped based enum
+QgsScaleComboBox.RatioMode.ForceUnitNumerator.__doc__ = "Default mode, forces the scale numerator to be 1, e.g. \"1:1000\""
+QgsScaleComboBox.RatioMode.Flexible.__doc__ = "Allows numerator values other than 1, e.g: \"2:3\"."
+QgsScaleComboBox.RatioMode.__doc__ = """Scale ratio modes.
+
+.. versionadded:: 4.0
+
+* ``ForceUnitNumerator``: Default mode, forces the scale numerator to be 1, e.g. \"1:1000\"
+* ``Flexible``: Allows numerator values other than 1, e.g: \"2:3\".
+
+"""
+# --
+QgsScaleComboBox.RatioMode.baseClass = QgsScaleComboBox
 try:
-    QgsScaleComboBox.__attribute_docs__ = {'scaleChanged': 'Emitted when *user* has finished editing/selecting a new scale. The\n``scale`` value indicates the scale denominator, e.g. 1000.0 for a\n1:1000 map.\n'}
+    QgsScaleComboBox.__attribute_docs__ = {'scaleChanged': 'Emitted when *user* has finished editing/selecting a new scale. The\n``scale`` value indicates the scale denominator, e.g. 1000.0 for a\n1:1000 map.\n', 'ratioModeChanged': 'Emitted when the ratio mode for the widget is changed.\n\n.. versionadded:: 4.0\n'}
     QgsScaleComboBox.toString = staticmethod(QgsScaleComboBox.toString)
     QgsScaleComboBox.toDouble = staticmethod(QgsScaleComboBox.toDouble)
     QgsScaleComboBox.__overridden_methods__ = ['showPopup']
-    QgsScaleComboBox.__signal_arguments__ = {'scaleChanged': ['scale: float']}
+    QgsScaleComboBox.__signal_arguments__ = {'scaleChanged': ['scale: float'], 'ratioModeChanged': ['mode: QgsScaleComboBox.RatioMode']}
 except (NameError, AttributeError):
     pass

python/gui/auto_generated/qgsscalecombobox.sip.in

@@ -20,6 +20,12 @@ highlights nearest to current scale value.
 #include "qgsscalecombobox.h"
 %End
   public:
+    enum class RatioMode
+    {
+      ForceUnitNumerator,
+      Flexible,
+    };
+
     QgsScaleComboBox( QWidget *parent /TransferThis/ = 0 );
 %Docstring
 Constructor for QgsScaleComboBox.
@@ -66,14 +72,16 @@ scale lower than the minimum scale will automatically be converted to
 the minimum scale. Except for 0 which is always allowed.
 %End
 
-    static QString toString( double scale );
+    static QString toString( double scale, QgsScaleComboBox::RatioMode mode = QgsScaleComboBox::RatioMode::ForceUnitNumerator );
 %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.
+Helper function to convert a ``scale`` double to scale string.
 
 The returned string will be rounded (e.g. 1:1000, not 1:1000.345).
 
+:param scale: scale value indicating the scale denominator, e.g. 1000.0
+              for a 1:1000 map.
+:param mode: ratio mode (since QGIS 4.0)
+
 .. seealso:: :py:func:`toDouble`
 %End
 
@@ -123,6 +131,15 @@ If ``scales`` is empty then the default user scale options will be used
 instead.
 
 .. versionadded:: 3.38
+%End
+
+    QgsScaleComboBox::RatioMode ratioMode() const;
+%Docstring
+Returns the ratio mode for the scale.
+
+.. seealso:: :py:func:`setRatioMode`
+
+.. versionadded:: 4.0
 %End
 
   signals:
@@ -132,6 +149,13 @@ instead.
 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
+
+    void ratioModeChanged( QgsScaleComboBox::RatioMode mode );
+%Docstring
+Emitted when the ratio mode for the widget is changed.
+
+.. versionadded:: 4.0
 %End
 
   public slots:
@@ -171,6 +195,15 @@ This only has an effect if :py:func:`~QgsScaleComboBox.allowNull` is
 .. seealso:: :py:func:`isNull`
 
 .. versionadded:: 3.8
+%End
+
+    void setRatioMode( QgsScaleComboBox::RatioMode mode );
+%Docstring
+Sets the ratio ``mode`` for the scale.
+
+.. seealso:: :py:func:`ratioMode`
+
+.. versionadded:: 4.0
 %End
 
   protected:

src/gui/qgsscalecombobox.cpp

@@ -20,6 +20,7 @@
 #include "qgsscalecombobox.h"
 #include "moc_qgsscalecombobox.cpp"
 #include "qgssettingsentryimpl.h"
+#include "qgsmathutils.h"
 
 #include <QAbstractItemView>
 #include <QLocale>
@@ -140,7 +141,7 @@ void QgsScaleComboBox::showPopup()
 
 QString QgsScaleComboBox::scaleString() const
 {
-  return toString( mScale );
+  return toString( mScale, mMode );
 }
 
 bool QgsScaleComboBox::setScaleString( const QString &string )
@@ -171,7 +172,7 @@ bool QgsScaleComboBox::setScaleString( const QString &string )
   else
   {
     mScale = newScale;
-    setEditText( toString( mScale ) );
+    setEditText( toString( mScale, mMode ) );
     clearFocus();
     if ( mScale != oldScale )
     {
@@ -193,7 +194,7 @@ bool QgsScaleComboBox::isNull() const
 
 void QgsScaleComboBox::setScale( double scale )
 {
-  setScaleString( toString( scale ) );
+  setScaleString( toString( scale, mMode ) );
 }
 
 void QgsScaleComboBox::fixupScale()
@@ -213,11 +214,21 @@ void QgsScaleComboBox::fixupScale()
   // Valid string representation
   if ( ok )
   {
-    // if a user types scale = 2345, we transform to 1:2345
-    if ( userSetScale && newScale < 1.0 && !qgsDoubleNear( newScale, 0.0 ) )
+    switch ( mMode )
     {
-      newScale = 1 / newScale;
+      case RatioMode::ForceUnitNumerator:
+      {
+        // if a user types scale = 2345, we transform to 1:2345
+        if ( userSetScale && newScale < 1.0 && !qgsDoubleNear( newScale, 0.0 ) )
+        {
+          newScale = 1 / newScale;
+        }
+        break;
+      }
+      case RatioMode::Flexible:
+        break;
     }
+
     setScale( newScale );
   }
   else
@@ -226,7 +237,22 @@ void QgsScaleComboBox::fixupScale()
   }
 }
 
-QString QgsScaleComboBox::toString( double scale )
+QgsScaleComboBox::RatioMode QgsScaleComboBox::ratioMode() const
+{
+  return mMode;
+}
+
+void QgsScaleComboBox::setRatioMode( QgsScaleComboBox::RatioMode mode )
+{
+  if ( mode == mMode )
+    return;
+
+  mMode = mode;
+  setScale( mScale );
+  emit ratioModeChanged( mMode );
+}
+
+QString QgsScaleComboBox::toString( double scale, RatioMode mode )
 {
   if ( std::isnan( scale ) )
   {
@@ -236,14 +262,31 @@ QString QgsScaleComboBox::toString( double scale )
   {
     return QStringLiteral( "0" );
   }
-  else if ( scale <= 1 )
-  {
-    return QStringLiteral( "%1:1" ).arg( QLocale().toString( static_cast<int>( std::round( 1.0 / scale ) ) ) );
-  }
-  else
+
+  switch ( mode )
   {
-    return QStringLiteral( "1:%1" ).arg( QLocale().toString( static_cast<float>( std::round( scale ) ), 'f', 0 ) );
+    case RatioMode::ForceUnitNumerator:
+      if ( scale <= 1 )
+      {
+        return QStringLiteral( "%1:1" ).arg( QLocale().toString( static_cast<int>( std::round( 1.0 / scale ) ) ) );
+      }
+      else
+      {
+        return QStringLiteral( "1:%1" ).arg( QLocale().toString( static_cast<float>( std::round( scale ) ), 'f', 0 ) );
+      }
+
+    case RatioMode::Flexible:
+    {
+      qlonglong numerator = 0;
+      qlonglong denominator = 0;
+      QgsMathUtils::doubleToRational( 1.0 / scale, numerator, denominator, 0.01 );
+      return QStringLiteral( "%1:%2" ).arg(
+        QLocale().toString( numerator ),
+        QLocale().toString( denominator )
+      );
+    }
   }
+  return QString();
 }
 
 double QgsScaleComboBox::toDouble( const QString &scaleString, bool *returnOk )