Add export layer settings to QgsLayoutContext

python/core/layout/qgslayoutcontext.sip

@@ -176,6 +176,29 @@ class QgsLayoutContext : QObject
  :rtype: bool
 %End
 
+    void setCurrentExportLayer( int layer = -1 );
+%Docstring
+ Sets the current item ``layer`` to draw while exporting. QgsLayoutItem subclasses
+ which support multi-layer SVG exports must check the currentExportLayer()
+ and customise their rendering based on the layer.
+
+ If ``layer`` is -1, all item layers will be rendered.
+
+.. seealso:: currentExportLayer()
+%End
+
+    int currentExportLayer() const;
+%Docstring
+ Returns the current item layer to draw while exporting. QgsLayoutItem subclasses
+ which support multi-layer SVG exports must check this
+ and customise their rendering based on the layer.
+
+ If ``layer`` is -1, all item layers should be rendered.
+
+.. seealso:: setCurrentExportLayer()
+ :rtype: int
+%End
+
   signals:
 
     void flagsChanged( QgsLayoutContext::Flags flags );

src/core/layout/qgslayoutcontext.h

@@ -188,6 +188,28 @@ class CORE_EXPORT QgsLayoutContext : public QObject
      */
     bool pagesVisible() const { return mPagesVisible; }
 
+    /**
+     * Sets the current item \a layer to draw while exporting. QgsLayoutItem subclasses
+     * which support multi-layer SVG exports must check the currentExportLayer()
+     * and customise their rendering based on the layer.
+     *
+     * If \a layer is -1, all item layers will be rendered.
+     *
+     * \see currentExportLayer()
+     */
+    void setCurrentExportLayer( int layer = -1 ) { mCurrentExportLayer = layer; }
+
+    /**
+     * Returns the current item layer to draw while exporting. QgsLayoutItem subclasses
+     * which support multi-layer SVG exports must check this
+     * and customise their rendering based on the layer.
+     *
+     * If \a layer is -1, all item layers should be rendered.
+     *
+     * \see setCurrentExportLayer()
+     */
+    int currentExportLayer() const { return mCurrentExportLayer; }
+
   signals:
 
     /**
@@ -200,6 +222,8 @@ class CORE_EXPORT QgsLayoutContext : public QObject
 
     Flags mFlags = 0;
 
+    int mCurrentExportLayer = -1;
+
     QgsFeature mFeature;
     QPointer< QgsVectorLayer > mLayer;
 

tests/src/core/testqgslayoutcontext.cpp

@@ -39,6 +39,7 @@ class TestQgsLayoutContext: public QObject
     void dpi();
     void renderContextFlags();
     void boundingBoxes();
+    void exportLayer();
 
   private:
     QString mReport;
@@ -180,5 +181,14 @@ void TestQgsLayoutContext::boundingBoxes()
   QVERIFY( context.boundingBoxesVisible() );
 }
 
+void TestQgsLayoutContext::exportLayer()
+{
+  QgsLayoutContext context;
+  // must default to -1
+  QCOMPARE( context.currentExportLayer(), -1 );
+  context.setCurrentExportLayer( 1 );
+  QCOMPARE( context.currentExportLayer(), 1 );
+}
+
 QGSTEST_MAIN( TestQgsLayoutContext )
 #include "testqgslayoutcontext.moc"