Add a fixed range width option to QgsRangeSlider

Allows forcing the widget to have a specific fixed range width,
so that interactions with the lower or upper slider automatically
force the other slider to move to keep a constant width

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

@@ -168,6 +168,32 @@ This corresponds to the larger increment or decrement applied when the user pres
 .. seealso:: :py:func:`setPageStep`
 
 .. seealso:: :py:func:`singleStep`
+%End
+
+    int fixedRangeWidth() const;
+%Docstring
+Returns the slider's fixed range width, or -1 if not set.
+
+If a fixed range width is set then moving either the lower or upper slider will automatically
+move the other slider accordingly, in order to keep the selected range at the specified
+fixed width.
+
+.. seealso:: :py:func:`setFixedRangeWidth`
+
+.. versionadded:: 3.38
+%End
+
+    void setFixedRangeWidth( int width );
+%Docstring
+Sets the slider's fixed range ``width``. Set to -1 if no fixed width is desired.
+
+If a fixed range width is set then moving either the lower or upper slider will automatically
+move the other slider accordingly, in order to keep the selected range at the specified
+fixed width.
+
+.. seealso:: :py:func:`fixedRangeWidth`
+
+.. versionadded:: 3.38
 %End
 
   public slots:
@@ -265,6 +291,17 @@ Emitted when the range selected in the widget is changed.
     void rangeLimitsChanged( int minimum, int maximum );
 %Docstring
 Emitted when the limits of values allowed in the widget is changed.
+%End
+
+    void fixedRangeWidthChanged( int width );
+%Docstring
+Emitted when the widget's fixed range width is changed.
+
+.. seealso:: :py:func:`fixedRangeWidth`
+
+.. seealso:: :py:func:`setFixedRangeWidth`
+
+.. versionadded:: 3.38
 %End
 
 };

python/gui/auto_generated/qgsrangeslider.sip.in

@@ -168,6 +168,32 @@ This corresponds to the larger increment or decrement applied when the user pres
 .. seealso:: :py:func:`setPageStep`
 
 .. seealso:: :py:func:`singleStep`
+%End
+
+    int fixedRangeWidth() const;
+%Docstring
+Returns the slider's fixed range width, or -1 if not set.
+
+If a fixed range width is set then moving either the lower or upper slider will automatically
+move the other slider accordingly, in order to keep the selected range at the specified
+fixed width.
+
+.. seealso:: :py:func:`setFixedRangeWidth`
+
+.. versionadded:: 3.38
+%End
+
+    void setFixedRangeWidth( int width );
+%Docstring
+Sets the slider's fixed range ``width``. Set to -1 if no fixed width is desired.
+
+If a fixed range width is set then moving either the lower or upper slider will automatically
+move the other slider accordingly, in order to keep the selected range at the specified
+fixed width.
+
+.. seealso:: :py:func:`fixedRangeWidth`
+
+.. versionadded:: 3.38
 %End
 
   public slots:
@@ -265,6 +291,17 @@ Emitted when the range selected in the widget is changed.
     void rangeLimitsChanged( int minimum, int maximum );
 %Docstring
 Emitted when the limits of values allowed in the widget is changed.
+%End
+
+    void fixedRangeWidthChanged( int width );
+%Docstring
+Emitted when the widget's fixed range width is changed.
+
+.. seealso:: :py:func:`fixedRangeWidth`
+
+.. seealso:: :py:func:`setFixedRangeWidth`
+
+.. versionadded:: 3.38
 %End
 
 };

src/gui/qgsrangeslider.cpp

@@ -120,7 +120,15 @@ void QgsRangeSlider::setLowerValue( int lowerValue )
     return;
 
   mLowerValue = std::min( mStyleOption.maximum, std::max( mStyleOption.minimum, lowerValue ) );
-  mUpperValue = std::max( mLowerValue, mUpperValue );
+  if ( mFixedRangeWidth >= 0 )
+  {
+    mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+    mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+  }
+  else
+  {
+    mUpperValue = std::max( mLowerValue, mUpperValue );
+  }
   emit rangeChanged( mLowerValue, mUpperValue );
   update();
 }
@@ -137,7 +145,16 @@ void QgsRangeSlider::setUpperValue( int upperValue )
     return;
 
   mUpperValue = std::max( mStyleOption.minimum, std::min( mStyleOption.maximum, upperValue ) );
-  mLowerValue = std::min( mLowerValue, mUpperValue );
+  if ( mFixedRangeWidth >= 0 )
+  {
+    mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+    mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+  }
+  else
+  {
+    mLowerValue = std::min( mLowerValue, mUpperValue );
+  }
+
   emit rangeChanged( mLowerValue, mUpperValue );
   update();
 }
@@ -152,6 +169,15 @@ void QgsRangeSlider::setRange( int lower, int upper )
 
   mLowerValue = std::min( mStyleOption.maximum, std::max( mStyleOption.minimum, lower ) );
   mUpperValue = std::min( mStyleOption.maximum, std::max( mStyleOption.minimum, upper ) );
+  if ( mFixedRangeWidth >= 0 )
+  {
+    mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+    mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+  }
+  else
+  {
+    mUpperValue = std::min( mStyleOption.maximum, std::max( mStyleOption.minimum, upper ) );
+  }
   emit rangeChanged( mLowerValue, mUpperValue );
   update();
 }
@@ -317,6 +343,24 @@ QRect QgsRangeSlider::selectedRangeRect()
   return selectionRect.adjusted( -1, 1, 1, -1 );
 }
 
+int QgsRangeSlider::fixedRangeWidth() const
+{
+  return mFixedRangeWidth;
+}
+
+void QgsRangeSlider::setFixedRangeWidth( int width )
+{
+  if ( width == mFixedRangeWidth )
+    return;
+
+  mFixedRangeWidth = width;
+
+  if ( mFixedRangeWidth >= 0 )
+    setUpperValue( mLowerValue + mFixedRangeWidth );
+
+  emit fixedRangeWidthChanged( mFixedRangeWidth );
+}
+
 void QgsRangeSlider::applyStep( int step )
 {
   switch ( mFocusControl )
@@ -327,6 +371,11 @@ void QgsRangeSlider::applyStep( int step )
       if ( newLowerValue != mLowerValue )
       {
         mLowerValue = newLowerValue;
+        if ( mFixedRangeWidth >= 0 )
+        {
+          mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+          mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+        }
         emit rangeChanged( mLowerValue, mUpperValue );
         update();
       }
@@ -339,6 +388,11 @@ void QgsRangeSlider::applyStep( int step )
       if ( newUpperValue != mUpperValue )
       {
         mUpperValue = newUpperValue;
+        if ( mFixedRangeWidth >= 0 )
+        {
+          mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+          mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+        }
         emit rangeChanged( mLowerValue, mUpperValue );
         update();
       }
@@ -354,7 +408,15 @@ void QgsRangeSlider::applyStep( int step )
         if ( newLowerValue != mLowerValue )
         {
           mLowerValue = newLowerValue;
-          mUpperValue = std::min( mStyleOption.maximum, mLowerValue + previousWidth );
+          if ( mFixedRangeWidth >= 0 )
+          {
+            mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+            mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+          }
+          else
+          {
+            mUpperValue = std::min( mStyleOption.maximum, mLowerValue + previousWidth );
+          }
           emit rangeChanged( mLowerValue, mUpperValue );
           update();
         }
@@ -366,7 +428,15 @@ void QgsRangeSlider::applyStep( int step )
         if ( newUpperValue != mUpperValue )
         {
           mUpperValue = newUpperValue;
-          mLowerValue = std::max( mStyleOption.minimum, mUpperValue - previousWidth );
+          if ( mFixedRangeWidth >= 0 )
+          {
+            mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+            mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+          }
+          else
+          {
+            mLowerValue = std::max( mStyleOption.minimum, mUpperValue - previousWidth );
+          }
           emit rangeChanged( mLowerValue, mUpperValue );
           update();
         }
@@ -604,6 +674,12 @@ void QgsRangeSlider::mouseMoveEvent( QMouseEvent *event )
       {
         changed = true;
         mUpperValue = mPreDragUpperValue;
+        if ( mFixedRangeWidth >= 0 )
+        {
+          // don't permit fixed width drags if it pushes the other value out of range
+          mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+          mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+        }
       }
     }
     else if ( newPosition > mStartDragPos )
@@ -614,6 +690,12 @@ void QgsRangeSlider::mouseMoveEvent( QMouseEvent *event )
       {
         changed = true;
         mLowerValue = mPreDragLowerValue;
+        if ( mFixedRangeWidth >= 0 )
+        {
+          // don't permit fixed width drags if it pushes the other value out of range
+          mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+          mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+        }
       }
     }
     else
@@ -623,11 +705,23 @@ void QgsRangeSlider::mouseMoveEvent( QMouseEvent *event )
       {
         changed = true;
         mUpperValue = mPreDragUpperValue;
+        if ( mFixedRangeWidth >= 0 )
+        {
+          // don't permit fixed width drags if it pushes the other value out of range
+          mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+          mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+        }
       }
       if ( mLowerValue != mPreDragLowerValue )
       {
         changed = true;
         mLowerValue = mPreDragLowerValue;
+        if ( mFixedRangeWidth >= 0 )
+        {
+          // don't permit fixed width drags if it pushes the other value out of range
+          mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+          mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+        }
       }
     }
   }
@@ -645,6 +739,13 @@ void QgsRangeSlider::mouseMoveEvent( QMouseEvent *event )
       if ( mLowerValue != newPosition )
       {
         mLowerValue = newPosition;
+        if ( mFixedRangeWidth >= 0 )
+        {
+          // don't permit fixed width drags if it pushes the other value out of range
+          mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+          mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+        }
+
         changed = true;
       }
       break;
@@ -657,6 +758,13 @@ void QgsRangeSlider::mouseMoveEvent( QMouseEvent *event )
       if ( mUpperValue != newPosition )
       {
         mUpperValue = newPosition;
+        if ( mFixedRangeWidth >= 0 )
+        {
+          // don't permit fixed width drags if it pushes the other value out of range
+          mLowerValue = std::max( mStyleOption.minimum, mUpperValue - mFixedRangeWidth );
+          mUpperValue = std::min( mLowerValue + mFixedRangeWidth, mStyleOption.maximum );
+        }
+
         changed = true;
       }
       break;

src/gui/qgsrangeslider.h

@@ -169,6 +169,30 @@ class GUI_EXPORT QgsRangeSlider : public QWidget
      */
     int pageStep() const;
 
+    /**
+     * Returns the slider's fixed range width, or -1 if not set.
+     *
+     * If a fixed range width is set then moving either the lower or upper slider will automatically
+     * move the other slider accordingly, in order to keep the selected range at the specified
+     * fixed width.
+     *
+     * \see setFixedRangeWidth()
+     * \since QGIS 3.38
+     */
+    int fixedRangeWidth() const;
+
+    /**
+     * Sets the slider's fixed range \a width. Set to -1 if no fixed width is desired.
+     *
+     * If a fixed range width is set then moving either the lower or upper slider will automatically
+     * move the other slider accordingly, in order to keep the selected range at the specified
+     * fixed width.
+     *
+     * \see fixedRangeWidth()
+     * \since QGIS 3.38
+     */
+    void setFixedRangeWidth( int width );
+
   public slots:
 
     /**
@@ -255,6 +279,16 @@ class GUI_EXPORT QgsRangeSlider : public QWidget
      */
     void rangeLimitsChanged( int minimum, int maximum );
 
+    /**
+     * Emitted when the widget's fixed range width is changed.
+     *
+     * \see fixedRangeWidth()
+     * \see setFixedRangeWidth()
+     *
+     * \since QGIS 3.38
+     */
+    void fixedRangeWidthChanged( int width );
+
   private:
 
     int pick( const QPoint &pt ) const;
@@ -270,6 +304,8 @@ class GUI_EXPORT QgsRangeSlider : public QWidget
     int mSingleStep = 1;
     int mPageStep = 10;
 
+    int mFixedRangeWidth = -1;
+
     QStyleOptionSlider mStyleOption;
     enum Control
     {

tests/src/python/test_qgsrangeslider.py

@@ -41,6 +41,10 @@ class TestQgsRangeSlider(QgisTestCase):
         w.setPageStep(5)
         self.assertEqual(w.pageStep(), 5)
 
+        self.assertEqual(w.fixedRangeWidth(), -1)
+        w.setFixedRangeWidth(5)
+        self.assertEqual(w.fixedRangeWidth(), 5)
+
     def testLimits(self):
         w = QgsRangeSlider()
         spy = QSignalSpy(w.rangeLimitsChanged)
@@ -268,6 +272,56 @@ class TestQgsRangeSlider(QgisTestCase):
         self.assertEqual(len(spy), 6)
         self.assertEqual(spy[-1], [3, 7])
 
+    def test_fixed_range_width(self):
+        """
+        Test interactions with fixed range widths
+        """
+        w = QgsRangeSlider()
+        w.setRangeLimits(0, 100)
+        w.setFixedRangeWidth(10)
+        self.assertEqual(w.upperValue() - w.lowerValue(), 10)
+
+        w.setUpperValue(70)
+        self.assertEqual(w.upperValue(), 70)
+        self.assertEqual(w.lowerValue(), 60)
+
+        w.setLowerValue(5)
+        self.assertEqual(w.upperValue(), 15)
+        self.assertEqual(w.lowerValue(), 5)
+
+        # try to force value outside range
+        w.setUpperValue(5)
+        self.assertEqual(w.upperValue(), 10)
+        self.assertEqual(w.lowerValue(), 0)
+
+        w.setLowerValue(95)
+        self.assertEqual(w.upperValue(), 100)
+        self.assertEqual(w.lowerValue(), 90)
+
+        w.setRange(0, 5)
+        self.assertEqual(w.upperValue(), 10)
+        self.assertEqual(w.lowerValue(), 0)
+
+        w.setRange(95, 100)
+        self.assertEqual(w.upperValue(), 100)
+        self.assertEqual(w.lowerValue(), 90)
+
+        # with zero width fixed range
+        w.setFixedRangeWidth(0)
+        self.assertEqual(w.upperValue() - w.lowerValue(), 0)
+
+        w.setUpperValue(70)
+        self.assertEqual(w.upperValue(), 70)
+        self.assertEqual(w.lowerValue(), 70)
+
+        w.setLowerValue(5)
+        self.assertEqual(w.upperValue(), 5)
+        self.assertEqual(w.lowerValue(), 5)
+
+        w.setRange(0, 5)
+        self.assertEqual(w.upperValue(), 0)
+        self.assertEqual(w.lowerValue(), 0)
+
 
 if __name__ == '__main__':
     unittest.main()