Add api to allow raster layer renderers to create different legend no…

…de types, instead of forcing them to always use the solid color blocks created by QgsRasterSymbolLegendNode
qgis · Dec 7, 2020 · 6932985 · 6932985
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commit 6932985
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diff --git a/python/core/auto_generated/raster/qgsrasterrenderer.sip.in b/python/core/auto_generated/raster/qgsrasterrenderer.sip.in
@@ -108,6 +108,18 @@ nodata values will be used.
     virtual void legendSymbologyItems( QList< QPair< QString, QColor > > &symbolItems /Out/ ) const;
 %Docstring
 Gets symbology items if provided by renderer
+%End
+
+    virtual QList<QgsLayerTreeModelLegendNode *> createLegendNodes( QgsLayerTreeLayer *nodeLayer ) /Factory/;
+%Docstring
+Creates a set of legend nodes representing the renderer.
+
+The default implementation calls :py:func:`~QgsRasterRenderer.legendSymbologyItems` and creates corresponding legend nodes for each returned
+symbology item.
+
+Subclasses can override this to return more legend nodes which better represent the renderer.
+
+.. versionadded:: 3.18
 %End
 
     virtual void readXml( const QDomElement &rendererElem );

diff --git a/src/core/qgsmaplayerlegend.cpp b/src/core/qgsmaplayerlegend.cpp
@@ -27,6 +27,7 @@
 #include "qgsdiagramrenderer.h"
 #include "qgssymbollayerutils.h"
 #include "qgspointcloudrenderer.h"
+#include "qgsrasterrenderer.h"
 
 QgsMapLayerLegend::QgsMapLayerLegend( QObject *parent )
   : QObject( parent )
@@ -426,28 +427,7 @@ QList<QgsLayerTreeModelLegendNode *> QgsDefaultRasterLayerLegend::createLayerTre
     nodes << new QgsWmsLegendNode( nodeLayer );
   }
 
-  QgsLegendColorList rasterItemList = mLayer->legendSymbologyItems();
-  if ( rasterItemList.isEmpty() )
-    return nodes;
-
-  // Paletted raster may have many colors, for example UInt16 may have 65536 colors
-  // and it is very slow, so we limit max count
-  int count = 0;
-  int max_count = 1000;
-
-  for ( QgsLegendColorList::const_iterator itemIt = rasterItemList.constBegin();
-        itemIt != rasterItemList.constEnd(); ++itemIt, ++count )
-  {
-    nodes << new QgsRasterSymbolLegendNode( nodeLayer, itemIt->second, itemIt->first );
-
-    if ( count == max_count )
-    {
-      QString label = tr( "following %1 items\nnot displayed" ).arg( rasterItemList.size() - max_count );
-      nodes << new QgsSimpleLegendNode( nodeLayer, label );
-      break;
-    }
-  }
-
+  nodes.append( mLayer->renderer()->createLegendNodes( nodeLayer ) );
   return nodes;
 }
 

diff --git a/src/core/raster/qgsrasterrenderer.cpp b/src/core/raster/qgsrasterrenderer.cpp
@@ -19,6 +19,7 @@
 #include "qgsrastertransparency.h"
 
 #include "qgssymbollayerutils.h"
+#include "qgslayertreemodellegendnode.h"
 
 #include <QCoreApplication>
 #include <QDomDocument>
@@ -101,6 +102,35 @@ void QgsRasterRenderer::setRasterTransparency( QgsRasterTransparency *t )
   mRasterTransparency = t;
 }
 
+QList<QgsLayerTreeModelLegendNode *> QgsRasterRenderer::createLegendNodes( QgsLayerTreeLayer *nodeLayer )
+{
+  QList<QgsLayerTreeModelLegendNode *> nodes;
+
+  QList< QPair< QString, QColor > > rasterItemList;
+  legendSymbologyItems( rasterItemList );
+  if ( rasterItemList.isEmpty() )
+    return nodes;
+
+  // Paletted raster may have many colors, for example UInt16 may have 65536 colors
+  // and it is very slow, so we limit max count
+  int count = 0;
+  int max_count = 1000;
+
+  for ( auto itemIt = rasterItemList.constBegin(); itemIt != rasterItemList.constEnd(); ++itemIt, ++count )
+  {
+    nodes << new QgsRasterSymbolLegendNode( nodeLayer, itemIt->second, itemIt->first );
+
+    if ( count == max_count )
+    {
+      QString label = tr( "following %1 items\nnot displayed" ).arg( rasterItemList.size() - max_count );
+      nodes << new QgsSimpleLegendNode( nodeLayer, label );
+      break;
+    }
+  }
+
+  return nodes;
+}
+
 void QgsRasterRenderer::_writeXml( QDomDocument &doc, QDomElement &rasterRendererElem ) const
 {
   if ( rasterRendererElem.isNull() )

diff --git a/src/core/raster/qgsrasterrenderer.h b/src/core/raster/qgsrasterrenderer.h
@@ -30,6 +30,8 @@ class QDomElement;
 class QPainter;
 class QgsRasterTransparency;
 class QgsStyleEntityVisitorInterface;
+class QgsLayerTreeModelLegendNode;
+class QgsLayerTreeLayer;
 
 /**
  * \ingroup core
@@ -119,6 +121,18 @@ class CORE_EXPORT QgsRasterRenderer : public QgsRasterInterface
     //! Gets symbology items if provided by renderer
     virtual void legendSymbologyItems( QList< QPair< QString, QColor > > &symbolItems SIP_OUT ) const { Q_UNUSED( symbolItems ) }
 
+    /**
+     * Creates a set of legend nodes representing the renderer.
+     *
+     * The default implementation calls legendSymbologyItems() and creates corresponding legend nodes for each returned
+     * symbology item.
+     *
+     * Subclasses can override this to return more legend nodes which better represent the renderer.
+     *
+     * \since QGIS 3.18
+     */
+    virtual QList<QgsLayerTreeModelLegendNode *> createLegendNodes( QgsLayerTreeLayer *nodeLayer ) SIP_FACTORY;
+
     //! Sets base class members from xml. Usually called from create() methods of subclasses
     void readXml( const QDomElement &rendererElem ) override;