[FEATURE] Add numeric formatter "fraction" style

This style represents decimal numbers as vulgar fractions, e.g. "3/4" instead of 0.75. Options include using Unicode superscript and subscript characters for nicer typography, e.g. ¹⁷/₂₃ (this is the default mode, disabling this option uses the "17/23" format). An option also exists for using dedicated unicode characters for specific fractions (where a unicode character exists), e.g. ½ or ¾ Ultimately this allows for creation of scalebars with fractional representations of distances, e.g. 0 ----- ½ ----- 1 km (instead of 0 ------ 0.5 ------ 1km) Fixes #21289 Sponsored by SLYR
qgis · Mar 23, 2020 · 78d445e · 78d445e
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diff --git a/python/core/auto_generated/numericformats/qgsfractionnumericformat.sip.in b/python/core/auto_generated/numericformats/qgsfractionnumericformat.sip.in
@@ -0,0 +1,172 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/numericformats/qgsfractionnumericformat.h                   *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/
+
+
+class QgsFractionNumericFormat : QgsNumericFormat
+{
+%Docstring
+A numeric formatter which returns a vulgar fractional representation of a decimal value (e.g. "1/2" instead of 0.5).
+
+.. versionadded:: 3.14
+%End
+
+%TypeHeaderCode
+#include "qgsfractionnumericformat.h"
+%End
+  public:
+
+    QgsFractionNumericFormat();
+%Docstring
+Default constructor
+%End
+
+    virtual QString id() const;
+
+    virtual QString visibleName() const;
+
+    virtual int sortKey();
+
+    virtual QString formatDouble( double value, const QgsNumericFormatContext &context ) const;
+
+    virtual QgsNumericFormat *clone() const /Factory/;
+
+    virtual QgsNumericFormat *create( const QVariantMap &configuration, const QgsReadWriteContext &context ) const /Factory/;
+
+    virtual QVariantMap configuration( const QgsReadWriteContext &context ) const;
+
+    virtual double suggestSampleValue() const;
+
+
+    bool useDedicatedUnicodeCharacters() const;
+%Docstring
+Returns ``True`` if dedicated unicode characters should be used, when the are available for the
+particular fraction (e.g. ½, ¼).
+
+.. seealso:: :py:func:`setUseDedicatedUnicodeCharacters`
+
+.. seealso:: :py:func:`useUnicodeSuperSubscript`
+%End
+
+    void setUseDedicatedUnicodeCharacters( bool enabled );
+%Docstring
+Sets whether dedicated unicode characters should be used, when the are available for the
+particular fraction (e.g. ½, ¼).
+
+.. seealso:: :py:func:`useDedicatedUnicodeCharacters`
+
+.. seealso:: :py:func:`setUseUnicodeSuperSubscript`
+%End
+
+    bool useUnicodeSuperSubscript() const;
+%Docstring
+Returns ``True`` if unicode superscript and subscript characters should be used, (e.g. "⁶/₇").
+
+.. seealso:: :py:func:`setUseUnicodeSuperSubscript`
+
+.. seealso:: :py:func:`useDedicatedUnicodeCharacters`
+%End
+
+    void setUseUnicodeSuperSubscript( bool enabled );
+%Docstring
+Sets whether unicode superscript and subscript characters should be used, (e.g. "⁶/₇").
+
+.. seealso:: :py:func:`useUnicodeSuperSubscript`
+
+.. seealso:: :py:func:`setUseDedicatedUnicodeCharacters`
+%End
+
+    bool showThousandsSeparator() const;
+%Docstring
+Returns ``True`` if the thousands grouping separator will be shown.
+
+.. seealso:: :py:func:`setShowThousandsSeparator`
+%End
+
+    void setShowThousandsSeparator( bool show );
+%Docstring
+Sets whether the thousands grouping separator will be shown.
+
+.. seealso:: :py:func:`showThousandsSeparator`
+%End
+
+    bool showPlusSign() const;
+%Docstring
+Returns ``True`` if a leading plus sign will be shown for positive values.
+
+.. seealso:: :py:func:`setShowPlusSign`
+%End
+
+    void setShowPlusSign( bool show );
+%Docstring
+Sets whether a leading plus sign will be shown for positive values.
+
+.. seealso:: :py:func:`showPlusSign`
+%End
+
+    QChar thousandsSeparator() const;
+%Docstring
+Returns any override for the thousands separator character. If an invalid QChar is returned,
+then the QGIS locale separator is used instead.
+
+.. seealso:: :py:func:`setThousandsSeparator`
+%End
+
+    void setThousandsSeparator( QChar character );
+%Docstring
+Sets an override ``character`` for the thousands separator character. If an invalid QChar is set,
+then the QGIS locale separator is used instead.
+
+.. seealso:: :py:func:`thousandsSeparator`
+%End
+
+    static bool doubleToVulgarFraction( const double value, unsigned long long &numerator /Out/, unsigned long long &denominator /Out/, int &sign /Out/, const double tolerance = 1e-10 );
+%Docstring
+Converts a double ``value`` to a vulgar fraction (e.g. ⅓, ¼, etc) by attempting to calculate
+the corresponding ``numerator`` and ``denominator``, within the specified ``tolerance``.
+
+This method is based of Richard's algorithm (1981) from "Continued Fractions without Tears" (University of Minnesota).
+
+:param value: input value to convert
+:param denominator: will be set to the calculated fraction denominator
+:param sign: will be set to the sign of the result (as -1 or +1 values)
+:param tolerance: acceptable tolerance. Larger values will give "nicer" fractions.
+
+:return: - ``True`` if ``value`` was successfully converted to a fraction
+         - numerator: will be set to calculated fraction numerator
+%End
+
+    static QString toUnicodeSuperscript( const QString &input );
+%Docstring
+Converts numbers in an ``input`` string to unicode superscript equivalents.
+
+.. seealso:: :py:func:`toUnicodeSubscript`
+%End
+
+    static QString toUnicodeSubscript( const QString &input );
+%Docstring
+Converts numbers in an ``input`` string to unicode subscript equivalents.
+
+.. seealso:: :py:func:`toUnicodeSuperscript`
+%End
+
+  protected:
+
+    virtual void setConfiguration( const QVariantMap &configuration, const QgsReadWriteContext &context );
+%Docstring
+Sets the format's ``configuration``.
+%End
+
+};
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/numericformats/qgsfractionnumericformat.h                   *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/
diff --git a/python/core/auto_generated/numericformats/qgsnumericformat.sip.in b/python/core/auto_generated/numericformats/qgsnumericformat.sip.in
@@ -168,6 +168,8 @@ This is an abstract base class and will always need to be subclassed.
       sipType = sipType_QgsCurrencyNumericFormat;
     else if ( dynamic_cast< QgsBasicNumericFormat * >( sipCpp ) )
       sipType = sipType_QgsBasicNumericFormat;
+    else if ( dynamic_cast< QgsFractionNumericFormat * >( sipCpp ) )
+      sipType = sipType_QgsFractionNumericFormat;
     else
       sipType = NULL;
 %End

diff --git a/python/core/core_auto.sip b/python/core/core_auto.sip
@@ -418,6 +418,7 @@
 %Include auto_generated/numericformats/qgsbearingnumericformat.sip
 %Include auto_generated/numericformats/qgscurrencynumericformat.sip
 %Include auto_generated/numericformats/qgsfallbacknumericformat.sip
+%Include auto_generated/numericformats/qgsfractionnumericformat.sip
 %Include auto_generated/numericformats/qgsnumericformat.sip
 %Include auto_generated/numericformats/qgsnumericformatregistry.sip
 %Include auto_generated/numericformats/qgspercentagenumericformat.sip

diff --git a/python/gui/auto_generated/numericformats/qgsnumericformatwidget.sip.in b/python/gui/auto_generated/numericformats/qgsnumericformatwidget.sip.in
@@ -7,6 +7,7 @@
  ************************************************************************/
 
 
+
 class QgsNumericFormatWidget : QgsPanelWidget
 {
 %Docstring
@@ -231,6 +232,33 @@ Constructor for QgsScientificNumericFormatWidget, initially showing the specifie
 };
 
 
+
+class QgsFractionNumericFormatWidget : QgsNumericFormatWidget
+{
+%Docstring
+A widget which allow control over the properties of a :py:class:`QgsFractionNumericFormat`.
+
+.. versionadded:: 3.14
+%End
+
+%TypeHeaderCode
+#include "qgsnumericformatwidget.h"
+%End
+  public:
+
+    QgsFractionNumericFormatWidget( const QgsNumericFormat *format, QWidget *parent /TransferThis/ = 0 );
+%Docstring
+Constructor for QgsFractionNumericFormatWidget, initially showing the specified ``format``.
+%End
+    ~QgsFractionNumericFormatWidget();
+
+    virtual void setFormat( QgsNumericFormat *format );
+
+
+    virtual QgsNumericFormat *format() /Factory/;
+
+
+};
 /************************************************************************
  * This file has been generated automatically from                      *
  *                                                                      *

diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
@@ -108,6 +108,7 @@ SET(QGIS_CORE_SRCS
   numericformats/qgsbearingnumericformat.cpp
   numericformats/qgscurrencynumericformat.cpp
   numericformats/qgsfallbacknumericformat.cpp
+  numericformats/qgsfractionnumericformat.cpp
   numericformats/qgsnumericformat.cpp
   numericformats/qgsnumericformatregistry.cpp
   numericformats/qgspercentagenumericformat.cpp
@@ -1184,6 +1185,7 @@ SET(QGIS_CORE_HDRS
   numericformats/qgsbearingnumericformat.h
   numericformats/qgscurrencynumericformat.h
   numericformats/qgsfallbacknumericformat.h
+  numericformats/qgsfractionnumericformat.h
   numericformats/qgsnumericformat.h
   numericformats/qgsnumericformatregistry.h
   numericformats/qgspercentagenumericformat.h