Add fixed range width option to QgsElevationControllerWidget

python/PyQt6/gui/auto_generated/elevation/qgselevationcontrollerwidget.sip.in

@@ -59,6 +59,15 @@ Returns a reference to the slider component of the widget.
 %Docstring
 Returns a reference to the widget's configuration menu, which can be used
 to add actions to the menu.
+%End
+
+    double fixedRangeWidth() const;
+%Docstring
+Returns the fixed range width, or -1 if no fixed width is set.
+
+A fixed width forces the selected elevation range to have a matching width.
+
+.. seealso:: :py:func:`setFixedRangeWidth`
 %End
 
   public slots:
@@ -77,6 +86,15 @@ Sets the current visible ``range`` for the widget.
 Sets the limits of the elevation range which can be selected by the widget.
 
 .. seealso:: :py:func:`rangeLimits`
+%End
+
+    void setFixedRangeWidth( double width );
+%Docstring
+Sets the fixed range ``width``. Set to -1 if no fixed width is desired.
+
+A fixed width forces the selected elevation range to have a matching width.
+
+.. seealso:: :py:func:`fixedRangeWidth`
 %End
 
   signals:

python/gui/auto_generated/elevation/qgselevationcontrollerwidget.sip.in

@@ -59,6 +59,15 @@ Returns a reference to the slider component of the widget.
 %Docstring
 Returns a reference to the widget's configuration menu, which can be used
 to add actions to the menu.
+%End
+
+    double fixedRangeWidth() const;
+%Docstring
+Returns the fixed range width, or -1 if no fixed width is set.
+
+A fixed width forces the selected elevation range to have a matching width.
+
+.. seealso:: :py:func:`setFixedRangeWidth`
 %End
 
   public slots:
@@ -77,6 +86,15 @@ Sets the current visible ``range`` for the widget.
 Sets the limits of the elevation range which can be selected by the widget.
 
 .. seealso:: :py:func:`rangeLimits`
+%End
+
+    void setFixedRangeWidth( double width );
+%Docstring
+Sets the fixed range ``width``. Set to -1 if no fixed width is desired.
+
+A fixed width forces the selected elevation range to have a matching width.
+
+.. seealso:: :py:func:`fixedRangeWidth`
 %End
 
   signals:

src/gui/elevation/qgselevationcontrollerwidget.cpp

@@ -102,7 +102,20 @@ QgsDoubleRange QgsElevationControllerWidget::range() const
   if ( snappedLower == mSlider->lowerValue() && snappedUpper == mSlider->upperValue() )
     return mCurrentRange;
 
-  return QgsDoubleRange( mSlider->lowerValue() / mSliderPrecision, mSlider->upperValue() / mSliderPrecision );
+  const QgsDoubleRange sliderRange( mSlider->lowerValue() / mSliderPrecision, mSlider->upperValue() / mSliderPrecision );
+  if ( mFixedRangeWidth >= 0 )
+  {
+    // adjust range so that it has exactly the fixed width (given slider int precision the slider range
+    // will not have the exact fixed width)
+    if ( sliderRange.upper() + mFixedRangeWidth <= mRangeLimits.upper() )
+      return QgsDoubleRange( sliderRange.lower(), sliderRange.lower() + mFixedRangeWidth );
+    else
+      return QgsDoubleRange( sliderRange.upper() - mFixedRangeWidth, sliderRange.upper() );
+  }
+  else
+  {
+    return sliderRange;
+  }
 }
 
 QgsDoubleRange QgsElevationControllerWidget::rangeLimits() const
@@ -180,6 +193,27 @@ void QgsElevationControllerWidget::updateWidgetMask()
   setMask( reg );
 }
 
+double QgsElevationControllerWidget::fixedRangeWidth() const
+{
+  return mFixedRangeWidth;
+}
+
+void QgsElevationControllerWidget::setFixedRangeWidth( double width )
+{
+  if ( width == mFixedRangeWidth )
+    return;
+
+  mFixedRangeWidth = width;
+  if ( mFixedRangeWidth < 0 )
+  {
+    mSlider->setFixedRangeWidth( -1 );
+  }
+  else
+  {
+    mSlider->setFixedRangeWidth( static_cast< int >( std::round( mFixedRangeWidth * mSliderPrecision ) ) );
+  }
+}
+
 //
 // QgsElevationControllerLabels
 //

src/gui/elevation/qgselevationcontrollerwidget.h

@@ -97,6 +97,15 @@ class GUI_EXPORT QgsElevationControllerWidget : public QWidget
      */
     QMenu *menu();
 
+    /**
+     * Returns the fixed range width, or -1 if no fixed width is set.
+     *
+     * A fixed width forces the selected elevation range to have a matching width.
+     *
+     * \see setFixedRangeWidth()
+     */
+    double fixedRangeWidth() const;
+
   public slots:
 
     /**
@@ -114,6 +123,15 @@ class GUI_EXPORT QgsElevationControllerWidget : public QWidget
      */
     void setRangeLimits( const QgsDoubleRange &limits );
 
+    /**
+     * Sets the fixed range \a width. Set to -1 if no fixed width is desired.
+     *
+     * A fixed width forces the selected elevation range to have a matching width.
+     *
+     * \see fixedRangeWidth()
+     */
+    void setFixedRangeWidth( double width );
+
   signals:
 
     /**
@@ -134,6 +152,7 @@ class GUI_EXPORT QgsElevationControllerWidget : public QWidget
     QgsElevationControllerLabels *mSliderLabels = nullptr;
     QgsDoubleRange mRangeLimits;
     QgsDoubleRange mCurrentRange;
+    double mFixedRangeWidth = -1;
     int mBlockSliderChanges = 0;
     double mSliderPrecision = 100;
 

tests/src/python/test_qgselevationcontrollerwidget.py

@@ -108,6 +108,20 @@ class TestQgsElevationControllerWidget(QgisTestCase):
         self.assertAlmostEqual(w.range().lower(), 459.644, 3)
         self.assertAlmostEqual(w.range().upper(), 729.495, 3)
 
+    def testFixedRangeWidth(self):
+        """
+        Test that fixed range width is correctly handled
+        """
+        w = QgsElevationControllerWidget()
+        w.setRangeLimits(QgsDoubleRange(100.5, 1000))
+        w.setFixedRangeWidth(10.0001)
+        self.assertEqual(w.fixedRangeWidth(), 10.0001)
+        w.setRange(QgsDoubleRange(130.3, 920.6))
+        self.assertAlmostEqual(w.range().upper() - w.range().lower(), 10.0001, 6)
+
+        w.slider().setLowerValue(50)
+        self.assertAlmostEqual(w.range().upper() - w.range().lower(), 10.0001, 6)
+
     def test_project_interaction(self):
         """
         Test interaction of widget with project