[feature] Add support for rounded corners for balloon callout styles

Allows for visually please rounded corners by exposing a "corner radius"
setting for balloon callouts.

python/core/auto_generated/callouts/qgscallout.sip.in

@@ -65,6 +65,7 @@ relevant symbology elements to render them.
       Orientation,
       Margins,
       WedgeWidth,
+      CornerRadius,
     };
 
     enum DrawOrder
@@ -987,7 +988,6 @@ Returns the units for the margins between the outside of the callout frame and t
 .. seealso:: :py:func:`margins`
 %End
 
-
     double wedgeWidth() const;
 %Docstring
 Returns the width of the wedge shape at the side it connects with the label.
@@ -1001,7 +1001,7 @@ Units are specified through :py:func:`~QgsBalloonCallout.wedgeWidthUnit`.
 
     void setWedgeWidth( double width );
 %Docstring
-Returns the ``width`` of the wedge shape at the side it connects with the label.
+Sets the ``width`` of the wedge shape at the side it connects with the label.
 
 Units are specified through :py:func:`~QgsBalloonCallout.setWedgeWidthUnit`.
 
@@ -1050,6 +1050,69 @@ Returns the map unit scale for the wedge width.
 .. seealso:: :py:func:`wedgeWidth`
 %End
 
+    double cornerRadius() const;
+%Docstring
+Returns the corner radius of the balloon shapes.
+
+Units are specified through :py:func:`~QgsBalloonCallout.wedgeWidthUnit`.
+
+.. seealso:: :py:func:`setCornerRadius`
+
+.. seealso:: :py:func:`cornerRadiusUnit`
+%End
+
+    void setCornerRadius( double radius );
+%Docstring
+Sets the ``radius`` of the corners for the balloon shapes.
+
+Units are specified through :py:func:`~QgsBalloonCallout.setCornerRadiusUnit`.
+
+.. seealso:: :py:func:`cornerRadius`
+
+.. seealso:: :py:func:`setCornerRadiusUnit`
+%End
+
+    void setCornerRadiusUnit( QgsUnitTypes::RenderUnit unit );
+%Docstring
+Sets the ``unit`` for the corner radius.
+
+.. seealso:: :py:func:`cornerRadiusUnit`
+
+.. seealso:: :py:func:`setCornerRadius`
+%End
+
+    QgsUnitTypes::RenderUnit cornerRadiusUnit() const;
+%Docstring
+Returns the units for the corner radius.
+
+.. seealso:: :py:func:`setCornerRadiusUnit`
+
+.. seealso:: :py:func:`cornerRadius`
+%End
+
+    void setCornerRadiusMapUnitScale( const QgsMapUnitScale &scale );
+%Docstring
+Sets the map unit ``scale`` for the corner radius.
+
+.. seealso:: :py:func:`cornerRadiusMapUnitScale`
+
+.. seealso:: :py:func:`setCornerRadiusUnit`
+
+.. seealso:: :py:func:`setCornerRadius`
+%End
+
+    const QgsMapUnitScale &cornerRadiusMapUnitScale() const;
+%Docstring
+Returns the map unit scale for the corner radius.
+
+.. seealso:: :py:func:`setCornerRadiusMapUnitScale`
+
+.. seealso:: :py:func:`cornerRadiusUnit`
+
+.. seealso:: :py:func:`cornerRadius`
+%End
+
+
   protected:
     virtual void draw( QgsRenderContext &context, const QRectF &bodyBoundingBox, const double angle, const QgsGeometry &anchor, QgsCallout::QgsCalloutContext &calloutContext );
 

src/core/callouts/qgscallout.cpp

@@ -63,6 +63,7 @@ void QgsCallout::initPropertyDefinitions()
       QgsCallout::Margins, QgsPropertyDefinition( "Margins", QgsPropertyDefinition::DataTypeString, QObject::tr( "Margins" ), QObject::tr( "string of four doubles '<b>top,right,bottom,left</b>' or array of doubles <b>[top, right, bottom, left]</b>" ) )
     },
     { QgsCallout::WedgeWidth, QgsPropertyDefinition( "WedgeWidth", QObject::tr( "Wedge width" ), QgsPropertyDefinition::DoublePositive, origin ) },
+    { QgsCallout::CornerRadius, QgsPropertyDefinition( "CornerRadius", QObject::tr( "Corner radius" ), QgsPropertyDefinition::DoublePositive, origin ) },
   };
 }
 
@@ -1021,6 +1022,9 @@ QgsBalloonCallout::QgsBalloonCallout( const QgsBalloonCallout &other )
   , mWedgeWidth( other.mWedgeWidth )
   , mWedgeWidthUnit( other.mWedgeWidthUnit )
   , mWedgeWidthScale( other.mWedgeWidthScale )
+  , mCornerRadius( other.mCornerRadius )
+  , mCornerRadiusUnit( other.mCornerRadiusUnit )
+  , mCornerRadiusScale( other.mCornerRadiusScale )
 {
 
 }
@@ -1062,6 +1066,10 @@ QVariantMap QgsBalloonCallout::properties( const QgsReadWriteContext &context )
   props[ QStringLiteral( "wedgeWidthUnit" ) ] = QgsUnitTypes::encodeUnit( mWedgeWidthUnit );
   props[ QStringLiteral( "wedgeWidthMapUnitScale" ) ] = QgsSymbolLayerUtils::encodeMapUnitScale( mWedgeWidthScale );
 
+  props[ QStringLiteral( "cornerRadius" ) ] = mCornerRadius;
+  props[ QStringLiteral( "cornerRadiusUnit" ) ] = QgsUnitTypes::encodeUnit( mCornerRadiusUnit );
+  props[ QStringLiteral( "cornerRadiusMapUnitScale" ) ] = QgsSymbolLayerUtils::encodeMapUnitScale( mCornerRadiusScale );
+
   return props;
 }
 
@@ -1087,6 +1095,10 @@ void QgsBalloonCallout::readProperties( const QVariantMap &props, const QgsReadW
   mWedgeWidth = props.value( QStringLiteral( "wedgeWidth" ), 2.64 ).toDouble();
   mWedgeWidthUnit = QgsUnitTypes::decodeRenderUnit( props.value( QStringLiteral( "wedgeWidthUnit" ) ).toString() );
   mWedgeWidthScale = QgsSymbolLayerUtils::decodeMapUnitScale( props.value( QStringLiteral( "wedgeWidthMapUnitScale" ) ).toString() );
+
+  mCornerRadius = props.value( QStringLiteral( "cornerRadius" ), 0 ).toDouble();
+  mCornerRadiusUnit = QgsUnitTypes::decodeRenderUnit( props.value( QStringLiteral( "cornerRadiusUnit" ) ).toString() );
+  mCornerRadiusScale = QgsSymbolLayerUtils::decodeMapUnitScale( props.value( QStringLiteral( "cornerRadiusMapUnitScale" ) ).toString() );
 }
 
 void QgsBalloonCallout::startRender( QgsRenderContext &context )
@@ -1181,6 +1193,14 @@ QPolygonF QgsBalloonCallout::getPoints( QgsRenderContext &context, QgsPointXY or
   }
   segmentPointWidth = context.convertToPainterUnits( segmentPointWidth, mWedgeWidthUnit, mWedgeWidthScale );
 
+  double cornerRadius = mCornerRadius;
+  if ( dataDefinedProperties().isActive( QgsCallout::CornerRadius ) )
+  {
+    context.expressionContext().setOriginalValueVariable( cornerRadius );
+    cornerRadius = dataDefinedProperties().valueAsDouble( QgsCallout::CornerRadius, context.expressionContext(), cornerRadius );
+  }
+  cornerRadius = context.convertToPainterUnits( cornerRadius, mCornerRadiusUnit, mCornerRadiusScale );
+
   double left = mMargins.left();
   double right = mMargins.right();
   double top = mMargins.top();
@@ -1247,10 +1267,14 @@ QPolygonF QgsBalloonCallout::getPoints( QgsRenderContext &context, QgsPointXY or
                              rect.width() + marginLeft + marginRight,
                              rect.height() - marginTop - marginBottom );
 
-  // IMPORTANT -- check for degenerate height is >=0, because QRectF are not normalized and we are using painter
+  // IMPORTANT -- check for degenerate height is sometimes >=0, because QRectF are not normalized and we are using painter
   // coordinates with descending vertical axis!
-  if ( expandedRect.width() <= 0 || expandedRect.height() >= 0 )
+  if ( expandedRect.width() <= 0 || ( rect.height() < 0 && expandedRect.height() >= 0 ) || ( rect.height() > 0 && expandedRect.height() <= 0 ) )
     return QPolygonF();
 
-  return QgsShapeGenerator::createBalloon( origin, expandedRect, segmentPointWidth );
+  const QPainterPath path = QgsShapeGenerator::createBalloon( origin, expandedRect, segmentPointWidth, cornerRadius );
+  QTransform t = QTransform::fromScale( 100, 100 );
+  QTransform ti = t.inverted();
+  QPolygonF poly = path.toFillPolygon( t );
+  return ti.map( poly );
 }

src/core/callouts/qgscallout.h

@@ -93,6 +93,7 @@ class CORE_EXPORT QgsCallout
       Orientation, //!< Orientation of curved line callouts (since QGIS 3.20)
       Margins, //!< Margin from text (since QGIS 3.20)
       WedgeWidth, //!< Balloon callout wedge width (since QGIS 3.20)
+      CornerRadius, //!< Balloon callout corner radius (since QGIS 3.20)
     };
 
     //! Options for draw order (stacking) of callouts
@@ -991,7 +992,6 @@ class CORE_EXPORT QgsBalloonCallout : public QgsCallout
     */
     QgsUnitTypes::RenderUnit marginsUnit() const { return mMarginUnit; }
 
-
     /**
      * Returns the width of the wedge shape at the side it connects with the label.
      *
@@ -1003,7 +1003,7 @@ class CORE_EXPORT QgsBalloonCallout : public QgsCallout
     double wedgeWidth() const { return mWedgeWidth; }
 
     /**
-     * Returns the \a width of the wedge shape at the side it connects with the label.
+     * Sets the \a width of the wedge shape at the side it connects with the label.
      *
      * Units are specified through setWedgeWidthUnit().
      *
@@ -1046,6 +1046,61 @@ class CORE_EXPORT QgsBalloonCallout : public QgsCallout
      */
     const QgsMapUnitScale &wedgeWidthMapUnitScale() const { return mWedgeWidthScale; }
 
+    /**
+     * Returns the corner radius of the balloon shapes.
+     *
+     * Units are specified through wedgeWidthUnit().
+     *
+     * \see setCornerRadius()
+     * \see cornerRadiusUnit()
+     */
+    double cornerRadius() const { return mCornerRadius; }
+
+    /**
+     * Sets the \a radius of the corners for the balloon shapes.
+     *
+     * Units are specified through setCornerRadiusUnit().
+     *
+     * \see cornerRadius()
+     * \see setCornerRadiusUnit()
+     */
+    void setCornerRadius( double radius ) { mCornerRadius = radius; }
+
+    /**
+     * Sets the \a unit for the corner radius.
+     *
+     * \see cornerRadiusUnit()
+     * \see setCornerRadius()
+    */
+    void setCornerRadiusUnit( QgsUnitTypes::RenderUnit unit ) { mCornerRadiusUnit = unit; }
+
+    /**
+     * Returns the units for the corner radius.
+     *
+     * \see setCornerRadiusUnit()
+     * \see cornerRadius()
+    */
+    QgsUnitTypes::RenderUnit cornerRadiusUnit() const { return mCornerRadiusUnit; }
+
+    /**
+     * Sets the map unit \a scale for the corner radius.
+     *
+     * \see cornerRadiusMapUnitScale()
+     * \see setCornerRadiusUnit()
+     * \see setCornerRadius()
+     */
+    void setCornerRadiusMapUnitScale( const QgsMapUnitScale &scale ) { mCornerRadiusScale = scale; }
+
+    /**
+     * Returns the map unit scale for the corner radius.
+     *
+     * \see setCornerRadiusMapUnitScale()
+     * \see cornerRadiusUnit()
+     * \see cornerRadius()
+     */
+    const QgsMapUnitScale &cornerRadiusMapUnitScale() const { return mCornerRadiusScale; }
+
+
   protected:
     void draw( QgsRenderContext &context, const QRectF &bodyBoundingBox, const double angle, const QgsGeometry &anchor, QgsCallout::QgsCalloutContext &calloutContext ) override;
 
@@ -1071,6 +1126,10 @@ class CORE_EXPORT QgsBalloonCallout : public QgsCallout
     QgsUnitTypes::RenderUnit mWedgeWidthUnit = QgsUnitTypes::RenderMillimeters;
     QgsMapUnitScale mWedgeWidthScale;
 
+    double mCornerRadius = 0.0;
+    QgsUnitTypes::RenderUnit mCornerRadiusUnit = QgsUnitTypes::RenderMillimeters;
+    QgsMapUnitScale mCornerRadiusScale;
+
 };