When rendering lower zoom level tiles vs actual render zoom level

due to presence of tilemap, ensure that we always use the actual
render zoom level to match styles for the tile instead of the
zoom level corresponding to the tile

Otherwise we'll be rendering different rules depending on the
actual tile source, when we should always use the actual
rules for the current map scale

python/core/auto_generated/vectortile/qgsvectortilerenderer.sip.in

@@ -42,6 +42,30 @@ Sets polygon of the tile
     QPolygon tilePolygon() const;
 %Docstring
 Returns polygon (made out of four corners of the tile) in screen coordinates calculated from render context
+%End
+
+    void setRenderZoomLevel( int level );
+%Docstring
+Sets the zoom level corresponding to the target render.
+
+This may differ from the tile's actual zoom leve when indexed tiles cause replacement of
+higher zoom level tiles with data from lower zoom level tiles.
+
+.. seealso:: :py:func:`renderZoomLevel`
+
+.. versionadded:: 3.32
+%End
+
+    int renderZoomLevel() const;
+%Docstring
+Returns the zoom level corresponding to the target render.
+
+This may differ from the tile's actual zoom leve when indexed tiles cause replacement of
+higher zoom level tiles with data from lower zoom level tiles.
+
+.. seealso:: :py:func:`setRenderZoomLevel`
+
+.. versionadded:: 3.32
 %End
 
     void setFields( const QMap<QString, QgsFields> &fields );

src/core/vectortile/qgsvectortilebasiclabeling.cpp

@@ -200,7 +200,7 @@ bool QgsVectorTileBasicLabelProvider::prepare( QgsRenderContext &context, QSet<Q
 void QgsVectorTileBasicLabelProvider::registerTileFeatures( const QgsVectorTileRendererData &tile, QgsRenderContext &context )
 {
   const QgsVectorTileFeatures tileData = tile.features();
-  int zoomLevel = tile.id().zoomLevel();
+  const int zoomLevel = tile.renderZoomLevel();
 
   for ( int i = 0; i < mStyles.count(); ++i )
   {

src/core/vectortile/qgsvectortilebasicrenderer.cpp

@@ -193,7 +193,7 @@ void QgsVectorTileBasicRenderer::renderBackground( QgsRenderContext &context )
 void QgsVectorTileBasicRenderer::renderTile( const QgsVectorTileRendererData &tile, QgsRenderContext &context )
 {
   const QgsVectorTileFeatures tileData = tile.features();
-  int zoomLevel = tile.id().zoomLevel();
+  const int zoomLevel = tile.renderZoomLevel();
 
   for ( const QgsVectorTileBasicRendererStyle &layerStyle : std::as_const( mStyles ) )
   {

src/core/vectortile/qgsvectortilelayerrenderer.cpp

@@ -229,6 +229,8 @@ void QgsVectorTileLayerRenderer::decodeAndDrawTile( const QgsVectorTileRawData &
   const QgsCoordinateTransform ct = ctx.coordinateTransform();
 
   QgsVectorTileRendererData tile( rawTile.id );
+  tile.setRenderZoomLevel( mTileZoom );
+
   tile.setFields( mPerLayerFields );
   tile.setFeatures( decoder.layerFeatures( mPerLayerFields, ct, &mRequiredLayers ) );
 

src/core/vectortile/qgsvectortilerenderer.h

@@ -42,6 +42,7 @@ class CORE_EXPORT QgsVectorTileRendererData
     //! Constructs the object
     explicit QgsVectorTileRendererData( QgsTileXYZ id )
       : mId( id )
+      , mRenderZoomLevel( id.zoomLevel() )
     {}
 
     //! Returns coordinates of the tile
@@ -52,6 +53,28 @@ class CORE_EXPORT QgsVectorTileRendererData
     //! Returns polygon (made out of four corners of the tile) in screen coordinates calculated from render context
     QPolygon tilePolygon() const { return mTilePolygon; }
 
+    /**
+     * Sets the zoom level corresponding to the target render.
+     *
+     * This may differ from the tile's actual zoom leve when indexed tiles cause replacement of
+     * higher zoom level tiles with data from lower zoom level tiles.
+     *
+     * \see renderZoomLevel()
+     * \since QGIS 3.32
+     */
+    void setRenderZoomLevel( int level ) { mRenderZoomLevel = level; }
+
+    /**
+     * Returns the zoom level corresponding to the target render.
+     *
+     * This may differ from the tile's actual zoom leve when indexed tiles cause replacement of
+     * higher zoom level tiles with data from lower zoom level tiles.
+     *
+     * \see setRenderZoomLevel()
+     * \since QGIS 3.32
+     */
+    int renderZoomLevel() const { return mRenderZoomLevel; }
+
     //! Sets per-layer fields
     void setFields( const QMap<QString, QgsFields> &fields ) { mFields = fields; }
     //! Returns per-layer fields
@@ -69,6 +92,13 @@ class CORE_EXPORT QgsVectorTileRendererData
   private:
     //! Position of the tile in the tile matrix set
     QgsTileXYZ mId;
+
+    /**
+     * Zoom level corresponding to the target render. This may differ from the tile's actual zoom leve when indexed tiles cause replacement of
+     * higher zoom level tiles with data from lower zoom level tiles.
+     */
+    int mRenderZoomLevel = -1;
+
     //! Per-layer fields
     QMap<QString, QgsFields> mFields;
     //! Features of the tile grouped into sub-layers