[layouts] Rework API for item export to multi-layered exports

Reworks the QgsLayoutItem API for handling multi-layered exports to work as an iterator. The advantage with this is that it avoids items needing to calculate in advance how many layers they require in the output file.
qgis · Aug 13, 2019 · 5660912 · 5660912
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diff --git a/python/core/auto_generated/layout/qgslayoutitem.sip.in b/python/core/auto_generated/layout/qgslayoutitem.sip.in
@@ -405,7 +405,7 @@ Returns the behavior of this item during exporting to layered exports (e.g. SVG)
 .. versionadded:: 3.10
 %End
 
-    virtual int numberExportLayers() const;
+ virtual int numberExportLayers() const /Deprecated/;
 %Docstring
 Returns the number of layers that this item requires for exporting during layered exports (e.g. SVG).
 Returns 0 if this item is to be placed on the same layer as the previous item,
@@ -417,6 +417,41 @@ their rendering to determine which layer should be drawn.
 .. seealso:: :py:func:`exportLayerBehavior`
 
 .. seealso:: :py:func:`exportLayerDetails`
+
+.. deprecated:: Use nextExportPart() and exportLayerBehavior() instead.
+%End
+
+    virtual void startLayeredExport();
+%Docstring
+Starts a multi-layer export operation.
+
+.. seealso:: :py:func:`stopLayeredExport`
+
+.. seealso:: :py:func:`nextExportPart`
+
+.. versionadded:: 3.10
+%End
+
+    virtual void stopLayeredExport();
+%Docstring
+Stops a multi-layer export operation.
+
+.. seealso:: :py:func:`startLayeredExport`
+
+.. seealso:: :py:func:`nextExportPart`
+
+.. versionadded:: 3.10
+%End
+
+    virtual bool nextExportPart();
+%Docstring
+Moves to the next export part for a multi-layered export item, during a multi-layered export.
+
+.. seealso:: :py:func:`startLayeredExport`
+
+.. seealso:: :py:func:`stopLayeredExport`
+
+.. versionadded:: 3.10
 %End
 
     struct ExportLayerDetail

diff --git a/python/core/auto_generated/layout/qgslayoutitemmap.sip.in b/python/core/auto_generated/layout/qgslayoutitemmap.sip.in
@@ -89,6 +89,12 @@ The caller takes responsibility for deleting the returned object.
 
     virtual int numberExportLayers() const;
 
+    virtual void startLayeredExport();
+
+    virtual void stopLayeredExport();
+
+    virtual bool nextExportPart();
+
     virtual ExportLayerBehavior exportLayerBehavior() const;
 
     virtual QgsLayoutItem::ExportLayerDetail exportLayerDetails( int layer ) const;

diff --git a/python/core/auto_generated/layout/qgslayoutrendercontext.sip.in b/python/core/auto_generated/layout/qgslayoutrendercontext.sip.in
@@ -183,7 +183,7 @@ whether they will be rendered in layout exports.
 .. seealso:: :py:func:`setPagesVisible`
 %End
 
-    void setCurrentExportLayer( int layer = -1 );
+ void setCurrentExportLayer( int layer = -1 ) /Deprecated/;
 %Docstring
 Sets the current item ``layer`` to draw while exporting. QgsLayoutItem subclasses
 which support multi-layer SVG exports must check the currentExportLayer()
@@ -192,9 +192,12 @@ and customize their rendering based on the layer.
 If ``layer`` is -1, all item layers will be rendered.
 
 .. seealso:: :py:func:`currentExportLayer`
+
+.. deprecated:: Items should now handle this themselves, via QgsLayoutItem.exportLayerBehavior() and
+returning :py:func:`QgsLayoutItem.nextExportPart()`
 %End
 
-    int currentExportLayer() const;
+ int currentExportLayer() const /Deprecated/;
 %Docstring
 Returns the current item layer to draw while exporting. QgsLayoutItem subclasses
 which support multi-layer SVG exports must check this
@@ -203,6 +206,9 @@ and customize their rendering based on the layer.
 If ``layer`` is -1, all item layers should be rendered.
 
 .. seealso:: :py:func:`setCurrentExportLayer`
+
+.. deprecated:: Items should now handle this themselves, via QgsLayoutItem.exportLayerBehavior() and
+returning :py:func:`QgsLayoutItem.nextExportPart()`
 %End
 
     QgsRenderContext::TextRenderFormat textRenderFormat() const;

diff --git a/src/core/layout/qgslayoutexporter.cpp b/src/core/layout/qgslayoutexporter.cpp
@@ -307,6 +307,7 @@ class LayoutContextSettingsRestorer
 {
   public:
 
+    Q_NOWARN_DEPRECATED_PUSH
     LayoutContextSettingsRestorer( QgsLayout *layout )
       : mLayout( layout )
       , mPreviousDpi( layout->renderContext().dpi() )
@@ -316,13 +317,16 @@ class LayoutContextSettingsRestorer
       , mPreviousSimplifyMethod( layout->renderContext().simplifyMethod() )
     {
     }
+    Q_NOWARN_DEPRECATED_POP
 
     ~LayoutContextSettingsRestorer()
     {
       mLayout->renderContext().setDpi( mPreviousDpi );
       mLayout->renderContext().setFlags( mPreviousFlags );
       mLayout->renderContext().setTextRenderFormat( mPreviousTextFormat );
+      Q_NOWARN_DEPRECATED_PUSH
       mLayout->renderContext().setCurrentExportLayer( mPreviousExportLayer );
+      Q_NOWARN_DEPRECATED_POP
       mLayout->renderContext().setSimplifyMethod( mPreviousSimplifyMethod );
     }
 
@@ -1582,16 +1586,29 @@ QgsLayoutExporter::ExportResult QgsLayoutExporter::handleLayeredExport( const QL
 
       if ( layoutItem && layoutItem->exportLayerBehavior() == QgsLayoutItem::ItemContainsSubLayers )
       {
-        for ( int layoutItemLayerIdx = 0; layoutItemLayerIdx < layoutItem->numberExportLayers(); layoutItemLayerIdx++ )
+        int layoutItemLayerIdx = 0;
+        Q_NOWARN_DEPRECATED_PUSH
+        mLayout->renderContext().setCurrentExportLayer( layoutItemLayerIdx );
+        Q_NOWARN_DEPRECATED_POP
+        layoutItem->startLayeredExport();
+        while ( layoutItem->nextExportPart() )
         {
+          Q_NOWARN_DEPRECATED_PUSH
           mLayout->renderContext().setCurrentExportLayer( layoutItemLayerIdx );
+          Q_NOWARN_DEPRECATED_POP
+
           layerDetails = layoutItem->exportLayerDetails( layoutItemLayerIdx );
           ExportResult result = exportFunc( layerId, layerDetails );
           if ( result != Success )
             return result;
           layerId++;
+
+          layoutItemLayerIdx++;
         }
+        Q_NOWARN_DEPRECATED_PUSH
         mLayout->renderContext().setCurrentExportLayer( -1 );
+        Q_NOWARN_DEPRECATED_POP
+        layoutItem->stopLayeredExport();
         currentLayerItems.clear();
       }
       else

diff --git a/src/core/layout/qgslayoutitem.cpp b/src/core/layout/qgslayoutitem.cpp
@@ -249,6 +249,34 @@ QgsLayoutItem::ExportLayerBehavior QgsLayoutItem::exportLayerBehavior() const
   return CanGroupWithAnyOtherItem;
 }
 
+int QgsLayoutItem::numberExportLayers() const
+{
+  return 0;
+}
+
+void QgsLayoutItem::startLayeredExport()
+{
+
+}
+
+void QgsLayoutItem::stopLayeredExport()
+{
+
+}
+
+bool QgsLayoutItem::nextExportPart()
+{
+  Q_NOWARN_DEPRECATED_PUSH
+  if ( !mLayout || mLayout->renderContext().currentExportLayer() == -1 )
+    return false;
+
+  // QGIS 4- return false from base class implementation
+
+  const int layers = numberExportLayers();
+  return mLayout->renderContext().currentExportLayer() < layers;
+  Q_NOWARN_DEPRECATED_POP
+}
+
 QgsLayoutItem::ExportLayerDetail QgsLayoutItem::exportLayerDetails( int ) const
 {
   return QgsLayoutItem::ExportLayerDetail();

diff --git a/src/core/layout/qgslayoutitem.h b/src/core/layout/qgslayoutitem.h
@@ -444,8 +444,37 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
      *
      * \see exportLayerBehavior()
      * \see exportLayerDetails()
+     *
+     * \deprecated Use nextExportPart() and exportLayerBehavior() instead.
+     */
+    Q_DECL_DEPRECATED virtual int numberExportLayers() const SIP_DEPRECATED;
+
+    /**
+     * Starts a multi-layer export operation.
+     *
+     * \see stopLayeredExport()
+     * \see nextExportPart()
+     * \since QGIS 3.10
+     */
+    virtual void startLayeredExport();
+
+    /**
+     * Stops a multi-layer export operation.
+     *
+     * \see startLayeredExport()
+     * \see nextExportPart()
+     * \since QGIS 3.10
+     */
+    virtual void stopLayeredExport();
+
+    /**
+     * Moves to the next export part for a multi-layered export item, during a multi-layered export.
+     *
+     * \see startLayeredExport()
+     * \see stopLayeredExport()
+     * \since QGIS 3.10
      */
-    virtual int numberExportLayers() const { return 0; }
+    virtual bool nextExportPart();
 
     /**
      * Contains details of a particular export layer relating to a layout item.