Correctly handle rendered item results stored when map canvas redraw

partially uses cached layer results

python/core/auto_generated/annotations/qgsrenderedannotationitemdetails.sip.in

@@ -33,14 +33,6 @@ Constructor for QgsRenderedAnnotationItemDetails.
     sipRes = PyUnicode_FromString( str.toUtf8().constData() );
 %End
 
-    virtual QgsRenderedAnnotationItemDetails *clone() const /Factory/;
-
-
-    QString layerId() const;
-%Docstring
-Returns the layer ID of the associated map layer.
-%End
-
     QString itemId() const;
 %Docstring
 Returns the item ID of the associated annotation item.

python/core/auto_generated/maprenderer/qgsmaprendererjob.sip.in

@@ -89,6 +89,16 @@ should be retained.
 .. seealso:: :py:func:`takeLabelingResults`
 
 .. versionadded:: 3.0
+%End
+
+    QStringList layersRedrawnFromCache() const;
+%Docstring
+Returns a list of the layer IDs for all layers which were redrawn from cached
+images.
+
+This method should only be called after the render job is completed.
+
+.. versionadded:: 3.22
 %End
 
     virtual QgsLabelingResults *takeLabelingResults() = 0 /Transfer/;
@@ -205,6 +215,7 @@ emitted when asynchronous rendering is finished (or canceled).
 
 
 
+
 
 
 };

python/core/auto_generated/maprenderer/qgsrendereditemresults.sip.in

@@ -39,6 +39,38 @@ Returns a list with details of the rendered annotation items within the specifie
 .. versionadded:: 3.22
 %End
 
+    void appendResults( const QList< QgsRenderedItemDetails * > &results /Transfer/, const QgsRenderContext &context );
+%Docstring
+Appends rendered item details to the results object.
+
+Ownership of ``results`` is transferred to the this object.
+
+The render ``context`` argument is used to specify the render context used to render the items. It will be used
+to transform the details to the destination map CRS.
+%End
+
+    void transferResults( QgsRenderedItemResults *other, const QStringList &layerIds );
+%Docstring
+Transfers all results from an ``other`` QgsRenderedItemResults object where the items
+have layer IDs matching the specified list.
+
+Items are removed from ``other`` and transferred to this object.
+
+.. warning::
+
+   After calling this method the ``other`` results will be left in an undefined state.
+%End
+
+    void transferResults( QgsRenderedItemResults *other );
+%Docstring
+Transfers all results from an ``other`` QgsRenderedItemResults object to this one.
+
+Items are removed from ``other`` and transferred to this object.
+
+.. warning::
+
+   After calling this method the ``other`` results will be left in an undefined state.
+%End
 
   private:
     QgsRenderedItemResults( const QgsRenderedItemResults & );

python/core/auto_generated/qgsrendereditemdetails.sip.in

@@ -9,6 +9,11 @@
 
 
 
+// this is needed for the "convert to subclass" code below to compile
+%ModuleHeaderCode
+#include "qgsrenderedannotationitemdetails.h"
+%End
+
 class QgsRenderedItemDetails
 {
 %Docstring(signature="appended")
@@ -29,11 +34,16 @@ Base class for detailed information about a rendered item.
       sipType = 0;
 %End
 
+    QgsRenderedItemDetails( const QString &layerId );
+%Docstring
+Constructor for QgsRenderedItemDetails.
+%End
+
     virtual ~QgsRenderedItemDetails();
 
-    virtual QgsRenderedItemDetails *clone() const = 0 /Factory/;
+    QString layerId() const;
 %Docstring
-Clones the details.
+Returns the layer ID of the associated map layer.
 %End
 
     QgsRectangle boundingBox() const;

src/core/annotations/qgsrenderedannotationitemdetails.cpp

@@ -17,13 +17,8 @@
 #include "qgsrenderedannotationitemdetails.h"
 
 QgsRenderedAnnotationItemDetails::QgsRenderedAnnotationItemDetails( const QString &layerId, const QString &itemId )
-  : mLayerId( layerId )
+  : QgsRenderedItemDetails( layerId )
   , mItemId( itemId )
 {
 
 }
-
-QgsRenderedAnnotationItemDetails *QgsRenderedAnnotationItemDetails::clone() const
-{
-  return new QgsRenderedAnnotationItemDetails( *this );
-}

src/core/annotations/qgsrenderedannotationitemdetails.h

@@ -43,21 +43,13 @@ class CORE_EXPORT QgsRenderedAnnotationItemDetails : public QgsRenderedItemDetai
     % End
 #endif
 
-    QgsRenderedAnnotationItemDetails *clone() const override SIP_FACTORY;
-
-    /**
-     * Returns the layer ID of the associated map layer.
-     */
-    QString layerId() const { return mLayerId; }
-
     /**
      * Returns the item ID of the associated annotation item.
      */
     QString itemId() const { return mItemId; }
 
   private:
 
-    QString mLayerId;
     QString mItemId;
 
 };

src/core/maprenderer/qgsmaprendererjob.cpp

@@ -147,6 +147,11 @@ void QgsMapRendererJob::start()
   }
 }
 
+QStringList QgsMapRendererJob::layersRedrawnFromCache() const
+{
+  return mLayersRedrawnFromCache;
+}
+
 QgsRenderedItemResults *QgsMapRendererJob::takeRenderedItemResults()
 {
   return mRenderedItemResults.release();
@@ -513,6 +518,7 @@ std::vector<LayerRenderJob> QgsMapRendererJob::prepareJobs( QPainter *painter, Q
       job.img->setDevicePixelRatio( static_cast<qreal>( mSettings.devicePixelRatio() ) );
       job.renderer = nullptr;
       job.context()->setPainter( nullptr );
+      mLayersRedrawnFromCache.append( ml->id() );
       continue;
     }
 

src/core/maprenderer/qgsmaprendererjob.h

@@ -287,6 +287,16 @@ class CORE_EXPORT QgsMapRendererJob : public QObject SIP_ABSTRACT
      */
     virtual bool usedCachedLabels() const = 0;
 
+    /**
+     * Returns a list of the layer IDs for all layers which were redrawn from cached
+     * images.
+     *
+     * This method should only be called after the render job is completed.
+     *
+     * \since QGIS 3.22
+     */
+    QStringList layersRedrawnFromCache() const;
+
     /**
      * Gets pointer to internal labeling engine (in order to get access to the results).
      * This should not be used if cached labeling was redrawn - see usedCachedLabels().
@@ -437,6 +447,8 @@ class CORE_EXPORT QgsMapRendererJob : public QObject SIP_ABSTRACT
     std::unique_ptr< QgsRenderedItemResults > mRenderedItemResults;
 #endif
 
+    QStringList mLayersRedrawnFromCache;
+
     /**
      * Prepares the cache for storing the result of labeling. Returns FALSE if
      * the render cannot use cached labels and should not cache the result.

src/core/maprenderer/qgsmaprenderersequentialjob.cpp

@@ -138,6 +138,7 @@ void QgsMapRendererSequentialJob::internalFinished()
 
   mLabelingResults.reset( mInternalJob->takeLabelingResults() );
   mUsedCachedLabels = mInternalJob->usedCachedLabels();
+  mLayersRedrawnFromCache = mInternalJob->layersRedrawnFromCache();
 
   mRenderedItemResults.reset( mInternalJob->takeRenderedItemResults() );
 

src/core/maprenderer/qgsrendereditemresults.cpp

@@ -126,4 +126,35 @@ void QgsRenderedItemResults::appendResults( const QList<QgsRenderedItemDetails *
   }
 }
 
+void QgsRenderedItemResults::transferResults( QgsRenderedItemResults *other, const QStringList &layerIds )
+{
+  for ( auto it = other->mDetails.begin(); it != other->mDetails.end(); )
+  {
+    if ( layerIds.contains( ( *it )->layerId() ) )
+    {
+      if ( QgsRenderedAnnotationItemDetails *annotationDetails = dynamic_cast< QgsRenderedAnnotationItemDetails * >( ( *it ).get() ) )
+        mAnnotationItemsIndex->insert( annotationDetails, annotationDetails->boundingBox() );
+
+      mDetails.emplace_back( std::move( *it ) );
+      other->mDetails.erase( it );
+    }
+    else
+    {
+      it++;
+    }
+  }
+}
+
+void QgsRenderedItemResults::transferResults( QgsRenderedItemResults *other )
+{
+  for ( auto it = other->mDetails.begin(); it != other->mDetails.end(); ++it )
+  {
+    if ( QgsRenderedAnnotationItemDetails *annotationDetails = dynamic_cast< QgsRenderedAnnotationItemDetails * >( ( *it ).get() ) )
+      mAnnotationItemsIndex->insert( annotationDetails, annotationDetails->boundingBox() );
+
+    mDetails.emplace_back( std::move( *it ) );
+  }
+  other->mDetails.clear();
+}
+
 

src/core/maprenderer/qgsrendereditemresults.h

@@ -61,20 +61,34 @@ class CORE_EXPORT QgsRenderedItemResults
      */
     QList<const QgsRenderedAnnotationItemDetails *> renderedAnnotationItemsInBounds( const QgsRectangle &bounds ) const;
 
-#ifndef SIP_RUN
-
     /**
      * Appends rendered item details to the results object.
      *
      * Ownership of \a results is transferred to the this object.
      *
      * The render \a context argument is used to specify the render context used to render the items. It will be used
      * to transform the details to the destination map CRS.
+     */
+    void appendResults( const QList< QgsRenderedItemDetails * > &results SIP_TRANSFER, const QgsRenderContext &context );
+
+    /**
+     * Transfers all results from an \a other QgsRenderedItemResults object where the items
+     * have layer IDs matching the specified list.
+     *
+     * Items are removed from \a other and transferred to this object.
      *
-     * \note Not available in Python bindings.
+     * \warning After calling this method the \a other results will be left in an undefined state.
      */
-    void appendResults( const QList< QgsRenderedItemDetails * > &results, const QgsRenderContext &context );
-#endif
+    void transferResults( QgsRenderedItemResults *other, const QStringList &layerIds );
+
+    /**
+     * Transfers all results from an \a other QgsRenderedItemResults object to this one.
+     *
+     * Items are removed from \a other and transferred to this object.
+     *
+     * \warning After calling this method the \a other results will be left in an undefined state.
+     */
+    void transferResults( QgsRenderedItemResults *other );
 
   private:
 #ifdef SIP_RUN

src/core/qgsrendereditemdetails.cpp

@@ -16,4 +16,10 @@
 
 #include "qgsrendereditemdetails.h"
 
+QgsRenderedItemDetails::QgsRenderedItemDetails( const QString &layerId )
+  : mLayerId( layerId )
+{
+
+}
+
 QgsRenderedItemDetails::~QgsRenderedItemDetails() = default;

src/core/qgsrendereditemdetails.h

@@ -21,6 +21,13 @@
 #include "qgis_sip.h"
 #include "qgsrectangle.h"
 
+#ifdef SIP_RUN
+// this is needed for the "convert to subclass" code below to compile
+% ModuleHeaderCode
+#include "qgsrenderedannotationitemdetails.h"
+% End
+#endif
+
 /**
  * \ingroup core
  * \brief Base class for detailed information about a rendered item.
@@ -39,12 +46,17 @@ class CORE_EXPORT QgsRenderedItemDetails
     SIP_END
 #endif
 
+    /**
+     * Constructor for QgsRenderedItemDetails.
+     */
+    QgsRenderedItemDetails( const QString &layerId );
+
     virtual ~QgsRenderedItemDetails();
 
     /**
-     * Clones the details.
+     * Returns the layer ID of the associated map layer.
      */
-    virtual QgsRenderedItemDetails *clone() const = 0 SIP_FACTORY;
+    QString layerId() const { return mLayerId; }
 
     /**
      * Returns the bounding box of the item (in map units).
@@ -62,6 +74,7 @@ class CORE_EXPORT QgsRenderedItemDetails
 
   private:
 
+    QString mLayerId;
     QgsRectangle mBounds;
 };
 

src/gui/qgsmapcanvas.cpp

@@ -495,11 +495,13 @@ void QgsMapCanvas::setCachingEnabled( bool enabled )
   if ( enabled )
   {
     mCache = new QgsMapRendererCache;
+    mPreviousRenderedItemResults = std::make_unique< QgsRenderedItemResults >();
   }
   else
   {
     delete mCache;
     mCache = nullptr;
+    mPreviousRenderedItemResults.reset();
   }
 }
 
@@ -512,6 +514,9 @@ void QgsMapCanvas::clearCache()
 {
   if ( mCache )
     mCache->clear();
+
+  if ( mPreviousRenderedItemResults )
+    mPreviousRenderedItemResults = std::make_unique< QgsRenderedItemResults >();
 }
 
 void QgsMapCanvas::setParallelRenderingEnabled( bool enabled )
@@ -707,7 +712,26 @@ void QgsMapCanvas::rendererJobFinished()
     }
     mLabelingResultsOutdated = false;
 
-    mRenderedItemResults.reset( mJob->takeRenderedItemResults() );
+    std::unique_ptr< QgsRenderedItemResults > renderedItemResults( mJob->takeRenderedItemResults() );
+    // if a layer was redrawn from the cached version, we should copy any existing rendered item results from that layer
+    if ( mRenderedItemResults )
+    {
+      renderedItemResults->transferResults( mRenderedItemResults.get(), mJob->layersRedrawnFromCache() );
+    }
+    if ( mPreviousRenderedItemResults )
+    {
+      // also transfer any results from previous renders which happened before this
+      renderedItemResults->transferResults( mPreviousRenderedItemResults.get(), mJob->layersRedrawnFromCache() );
+    }
+    if ( mRenderedItemResults && mPreviousRenderedItemResults )
+    {
+      // for other layers which ARE present in the most recent rendered item results BUT were not part of this render, we
+      // store the results in a temporary store in case they are later switched back on and the layer's image is taken
+      // from the cache
+      mPreviousRenderedItemResults->transferResults( mRenderedItemResults.get() );
+    }
+
+    mRenderedItemResults = std::move( renderedItemResults );
     mRenderedItemResultsOutdated = false;
 
     QImage img = mJob->renderedImage();

src/gui/qgsmapcanvas.h

@@ -1319,6 +1319,12 @@ class GUI_EXPORT QgsMapCanvas : public QGraphicsView, public QgsExpressionContex
      */
     std::unique_ptr< QgsRenderedItemResults > mRenderedItemResults;
 
+    /**
+     * Rendered results stored from previously rendered maps
+     * \since QGIS 3.22
+     */
+    std::unique_ptr< QgsRenderedItemResults > mPreviousRenderedItemResults;
+
     /**
      * TRUE if the rendered item results stored in mRenderedItemResults are outdated (e.g. as a result of an ongoing canvas render)
      *