[Backport queued_ltr_backports] Fix bug with inverted polygon renderer vs OTF simplification

python/PyQt6/core/auto_generated/qgsrendercontext.sip.in

@@ -635,7 +635,7 @@ Sets whether the rendering optimization (geometry simplification) should be exec
 .. seealso:: :py:func:`useRenderingOptimization`
 %End
 
-    const QgsVectorSimplifyMethod &vectorSimplifyMethod() const;
+    QgsVectorSimplifyMethod &vectorSimplifyMethod();
 %Docstring
 Returns the simplification settings to use when rendering vector layers.
 
@@ -646,6 +646,7 @@ The default is to use no simplification.
 .. versionadded:: 2.4
 %End
 
+
     void setVectorSimplifyMethod( const QgsVectorSimplifyMethod &simplifyMethod );
 %Docstring
 Sets the simplification setting to use when rendering vector layers.

python/core/auto_generated/qgsrendercontext.sip.in

@@ -635,7 +635,7 @@ Sets whether the rendering optimization (geometry simplification) should be exec
 .. seealso:: :py:func:`useRenderingOptimization`
 %End
 
-    const QgsVectorSimplifyMethod &vectorSimplifyMethod() const;
+    QgsVectorSimplifyMethod &vectorSimplifyMethod();
 %Docstring
 Returns the simplification settings to use when rendering vector layers.
 
@@ -646,6 +646,7 @@ The default is to use no simplification.
 .. versionadded:: 2.4
 %End
 
+
     void setVectorSimplifyMethod( const QgsVectorSimplifyMethod &simplifyMethod );
 %Docstring
 Sets the simplification setting to use when rendering vector layers.

src/core/qgsrendercontext.h

@@ -653,7 +653,16 @@ class CORE_EXPORT QgsRenderContext : public QgsTemporalRangeObject
      * \see setVectorSimplifyMethod()
      * \since QGIS 2.4
      */
-    const QgsVectorSimplifyMethod &vectorSimplifyMethod() const { return mVectorSimplifyMethod; }
+    QgsVectorSimplifyMethod &vectorSimplifyMethod() { return mVectorSimplifyMethod; }
+
+    /**
+     * Returns the simplification settings to use when rendering vector layers.
+     *
+     * The default is to use no simplification.
+     *
+     * \see setVectorSimplifyMethod()
+     */
+    const QgsVectorSimplifyMethod &vectorSimplifyMethod() const SIP_SKIP { return mVectorSimplifyMethod; }
 
     /**
      * Sets the simplification setting to use when rendering vector layers.

src/core/symbology/qgsmergedfeaturerenderer.cpp

@@ -26,6 +26,7 @@
 #include "qgspainteffect.h"
 #include "qgspainteffectregistry.h"
 #include "qgsstyleentityvisitor.h"
+#include "qgsmaptopixelgeometrysimplifier.h"
 
 #include <QDomDocument>
 #include <QDomElement>
@@ -232,6 +233,20 @@ bool QgsMergedFeatureRenderer::renderFeature( const QgsFeature &feature, QgsRend
   }
   QgsGeometry geom = feature.geometry();
 
+  // Simplify the geometry, if needed.
+  if ( context.vectorSimplifyMethod().forceLocalOptimization() )
+  {
+    const int simplifyHints = context.vectorSimplifyMethod().simplifyHints();
+    const QgsMapToPixelSimplifier simplifier( simplifyHints, context.vectorSimplifyMethod().tolerance(),
+        context.vectorSimplifyMethod().simplifyAlgorithm() );
+
+    QgsGeometry simplified( simplifier.simplify( geom ) );
+    if ( !simplified.isEmpty() )
+    {
+      geom = simplified;
+    }
+  }
+
   QgsCoordinateTransform xform = context.coordinateTransform();
   if ( xform.isValid() )
   {
@@ -366,7 +381,11 @@ void QgsMergedFeatureRenderer::stopRender( QgsRenderContext &context )
     if ( feat.hasGeometry() )
     {
       mContext.expressionContext().setFeature( feat );
+      const bool prevSimplify = context.vectorSimplifyMethod().forceLocalOptimization();
+      // we've already simplified, no need to re-do simplification
+      mContext.vectorSimplifyMethod().setForceLocalOptimization( false );
       mSubRenderer->renderFeature( feat, mContext );
+      mContext.vectorSimplifyMethod().setForceLocalOptimization( prevSimplify );
     }
   }
 

tests/src/core/testqgsinvertedpolygonrenderer.cpp

@@ -28,7 +28,9 @@
 #include <qgsproviderregistry.h>
 #include <qgsproject.h>
 #include "qgsrenderer.h"
-
+#include "qgsfillsymbol.h"
+#include "qgsinvertedpolygonrenderer.h"
+#include "qgssinglesymbolrenderer.h"
 //qgis test includes
 #include "qgsmultirenderchecker.h"
 
@@ -41,7 +43,7 @@ class TestQgsInvertedPolygon : public QgsTest
     Q_OBJECT
 
   public:
-    TestQgsInvertedPolygon() : QgsTest( QStringLiteral( "Inverted Polygon Renderer Tests" ) ) {}
+    TestQgsInvertedPolygon() : QgsTest( QStringLiteral( "Inverted Polygon Renderer Tests" ), QStringLiteral( "symbol_invertedpolygon" ) ) {}
 
   private slots:
     void initTestCase();// will be called before the first testfunction is executed.
@@ -52,6 +54,7 @@ class TestQgsInvertedPolygon : public QgsTest
     void checkSymbolItem();
     void preprocess();
     void projectionTest();
+    void projectionWithSimplificationTest();
     void curvedPolygons();
     void rotationTest();
 
@@ -136,6 +139,34 @@ void TestQgsInvertedPolygon::projectionTest()
   mMapSettings.setDestinationCrs( mpPolysLayer->crs() );
 }
 
+void TestQgsInvertedPolygon::projectionWithSimplificationTest()
+{
+  std::unique_ptr< QgsVectorLayer > polyLayer = std::make_unique< QgsVectorLayer >( testDataPath( "polys.shp" ), QStringLiteral( "polys" ) );
+  QVERIFY( polyLayer->isValid() );
+  QgsMapSettings mapSettings;
+  mapSettings.setDestinationCrs( QgsCoordinateReferenceSystem( QStringLiteral( "EPSG:4326" ) ) );
+  mapSettings.setLayers( QList<QgsMapLayer *>() << polyLayer.get() );
+  mapSettings.setOutputDpi( 96 );
+
+  QgsFillSymbol *fill = QgsFillSymbol::createSimple( QVariantMap( {{"color", "#fdbf6f"}, {"outline_color", "black"},
+    { "outline_width", "1"}} ) );
+  QgsInvertedPolygonRenderer *renderer = new QgsInvertedPolygonRenderer();
+  QgsSingleSymbolRenderer *singleSymbolRenderer = new QgsSingleSymbolRenderer( fill );
+  renderer->setEmbeddedRenderer( singleSymbolRenderer );
+  polyLayer->setRenderer( renderer );
+
+  mapSettings.setExtent( QgsRectangle( -119.552, 25.255, -109.393, 32.651 ) );
+
+  QgsVectorSimplifyMethod simplifyMethod;
+  simplifyMethod.setSimplifyHints( QgsVectorSimplifyMethod::GeometrySimplification );
+  simplifyMethod.setForceLocalOptimization( true );
+  simplifyMethod.setSimplifyAlgorithm( QgsVectorSimplifyMethod::SnappedToGridGlobal );
+  simplifyMethod.setThreshold( 0.1f );
+  mapSettings.setSimplifyMethod( simplifyMethod );
+
+  QGSVERIFYRENDERMAPSETTINGSCHECK( QStringLiteral( "inverted_polys_projection_simplification" ), QStringLiteral( "inverted_polys_projection_simplification" ), mapSettings );
+}
+
 void TestQgsInvertedPolygon::curvedPolygons()
 {
   const QString myCurvedPolysFileName = mTestDataDir + "curved_polys.gpkg";