[needs-docs] Remove option to show raster preview icons in layer tree

This option is not safe - see #16803, and generally undesirable
due to how slow generating the preview icons are

doc/api_break.dox

@@ -1566,6 +1566,7 @@ QgsLayerTreeModel        {#qgis_api_break_3_0_QgsLayerTreeMode}
 -----------------
 
 - The ShowSymbology flag was removed. Use ShowLegend instead.
+- The ShowRasterPreviewIcon was removed. This is no longer supported.
 - The AllowSymbologyChangeState flag was removed. Use AllowLegendChangeState instead.
 - legendFilterByMap() was renamed to legendFilterMapSettings()
 - isIndexSymbologyNode() was removed. Use index2legendNode() instead.
@@ -1575,6 +1576,7 @@ QgsLayerTreeModel        {#qgis_api_break_3_0_QgsLayerTreeMode}
 - autoCollapseSymbologyNodes() was removed. Use autoCollapseLegendNodes() instead.
 - the constructor takes a `QgsLayerTree*` instead of a `QgsLayerTreeGroup*`
 
+
 QgsLayerTreeModelLegendNode        {#qgis_api_break_3_0_QgsLayerTreeModelLegendNode}
 ---------------------------
 

python/core/layertree/qgslayertreemodel.sip

@@ -77,7 +77,6 @@ class QgsLayerTreeModel : QAbstractItemModel
     {
       // display
       ShowLegend,
-      ShowRasterPreviewIcon,
       ShowLegendAsTree,
       DeferredLegendInvalidation,
       UseEmbeddedWidgets,

src/app/qgisapp.cpp

@@ -3686,8 +3686,6 @@ void QgisApp::setupLayerTreeViewFromSettings()
   QgsSettings s;
 
   QgsLayerTreeModel *model = mLayerTreeView->layerTreeModel();
-  model->setFlag( QgsLayerTreeModel::ShowRasterPreviewIcon, s.value( QStringLiteral( "/qgis/createRasterLegendIcons" ), false ).toBool() );
-
   QFont fontLayer, fontGroup;
   fontLayer.setBold( true );
   fontGroup.setBold( false );

src/app/qgsoptions.cpp

@@ -673,7 +673,6 @@ QgsOptions::QgsOptions( QWidget *parent, Qt::WindowFlags fl, const QList<QgsOpti
   cbxAddPostgisDC->setChecked( mSettings->value( QStringLiteral( "/qgis/addPostgisDC" ), false ).toBool() );
   cbxAddOracleDC->setChecked( mSettings->value( QStringLiteral( "/qgis/addOracleDC" ), false ).toBool() );
   cbxCompileExpressions->setChecked( mSettings->value( QStringLiteral( "/qgis/compileExpressions" ), true ).toBool() );
-  cbxCreateRasterLegendIcons->setChecked( mSettings->value( QStringLiteral( "/qgis/createRasterLegendIcons" ), false ).toBool() );
 
   mComboCopyFeatureFormat->addItem( tr( "Plain text, no geometry" ), QgsClipboard::AttributesOnly );
   mComboCopyFeatureFormat->addItem( tr( "Plain text, WKT geometry" ), QgsClipboard::AttributesWithWKT );
@@ -1283,8 +1282,6 @@ void QgsOptions::saveOptions()
   mSettings->setValue( QStringLiteral( "/qgis/addOracleDC" ), cbxAddOracleDC->isChecked() );
   mSettings->setValue( QStringLiteral( "/qgis/compileExpressions" ), cbxCompileExpressions->isChecked() );
   mSettings->setValue( QStringLiteral( "/qgis/defaultLegendGraphicResolution" ), mLegendGraphicResolutionSpinBox->value() );
-  bool createRasterLegendIcons = mSettings->value( QStringLiteral( "/qgis/createRasterLegendIcons" ), false ).toBool();
-  mSettings->setValue( QStringLiteral( "/qgis/createRasterLegendIcons" ), cbxCreateRasterLegendIcons->isChecked() );
   mSettings->setValue( QStringLiteral( "/qgis/copyFeatureFormat" ), mComboCopyFeatureFormat->currentData().toInt() );
 
   mSettings->setValue( QStringLiteral( "/qgis/new_layers_visible" ), chkAddedVisibility->isChecked() );
@@ -1549,8 +1546,7 @@ void QgsOptions::saveOptions()
     saveGdalDriverList();
 
   // refresh symbology for any legend items, only if needed
-  if ( showLegendClassifiers != cbxLegendClassifiers->isChecked()
+  if ( showLegendClassifiers != cbxLegendClassifiers->isChecked() )
-       || createRasterLegendIcons != cbxCreateRasterLegendIcons->isChecked() )
   {
     // TODO[MD] QgisApp::instance()->legend()->updateLegendItemSymbologies();
   }

src/core/layertree/qgslayertreemodel.cpp

@@ -195,15 +195,7 @@ QVariant QgsLayerTreeModel::data( const QModelIndex &index, int role ) const
       // icons possibly overriding default icon
       if ( layer->type() == QgsMapLayer::RasterLayer )
       {
-        if ( testFlag( ShowRasterPreviewIcon ) )
+        return QgsLayerItem::iconRaster();
-        {
-          QgsRasterLayer *rlayer = qobject_cast<QgsRasterLayer *>( layer );
-          return QIcon( QPixmap::fromImage( rlayer->previewAsImage( QSize( 32, 32 ) ) ) );
-        }
-        else
-        {
-          return QgsLayerItem::iconRaster();
-        }
       }
 
       QgsVectorLayer *vlayer = dynamic_cast<QgsVectorLayer *>( layer );

src/core/layertree/qgslayertreemodel.h

@@ -96,7 +96,6 @@ class CORE_EXPORT QgsLayerTreeModel : public QAbstractItemModel
     {
       // display flags
       ShowLegend                 = 0x0001,  //!< Add legend nodes for layer nodes
-      ShowRasterPreviewIcon      = 0x0002,  //!< Will use real preview of raster layer as icon (may be slow)
       ShowLegendAsTree           = 0x0004,  //!< For legends that support it, will show them in a tree instead of a list (needs also ShowLegend). Added in 2.8
       DeferredLegendInvalidation = 0x0008,  //!< Defer legend model invalidation
       UseEmbeddedWidgets         = 0x0010,  //!< Layer nodes may optionally include extra embedded widgets (if used in QgsLayerTreeView). Added in 2.16

src/ui/qgsoptionsbase.ui

@@ -2681,8 +2681,8 @@
                <rect>
                 <x>0</x>
                 <y>0</y>
-                <width>741</width>
+                <width>269</width>
-                <height>779</height>
+                <height>424</height>
                </rect>
               </property>
               <layout class="QHBoxLayout" name="horizontalLayout_46">
@@ -2991,27 +2991,7 @@
                    </layout>
                   </item>
                   <item>
-                   <layout class="QGridLayout" name="gridLayout_3" columnminimumwidth="0,1,0">
+                   <layout class="QGridLayout" name="gridLayout_3" columnstretch="0,1,0">
-                    <item row="1" column="1" colspan="2">
-                     <widget class="QCheckBox" name="cbxLegendClassifiers">
-                      <property name="text">
-                       <string>Display classification attribute names</string>
-                      </property>
-                     </widget>
-                    </item>
-                    <item row="0" column="0" colspan="3">
-                     <widget class="QLabel" name="label_53">
-                      <property name="sizePolicy">
-                       <sizepolicy hsizetype="Minimum" vsizetype="Preferred">
-                        <horstretch>0</horstretch>
-                        <verstretch>0</verstretch>
-                       </sizepolicy>
-                      </property>
-                      <property name="text">
-                       <string>Legend item styles</string>
-                      </property>
-                     </widget>
-                    </item>
                     <item row="1" column="0">
                      <spacer name="horizontalSpacer_34">
                       <property name="orientation">
@@ -3028,10 +3008,23 @@
                       </property>
                      </spacer>
                     </item>
-                    <item row="2" column="1" colspan="2">
+                    <item row="0" column="0" colspan="3">
-                     <widget class="QCheckBox" name="cbxCreateRasterLegendIcons">
+                     <widget class="QLabel" name="label_53">
+                      <property name="sizePolicy">
+                       <sizepolicy hsizetype="Minimum" vsizetype="Preferred">
+                        <horstretch>0</horstretch>
+                        <verstretch>0</verstretch>
+                       </sizepolicy>
+                      </property>
                       <property name="text">
-                       <string>Create raster icons (may be slow)</string>
+                       <string>Legend item styles</string>
+                      </property>
+                     </widget>
+                    </item>
+                    <item row="1" column="1" colspan="2">
+                     <widget class="QCheckBox" name="cbxLegendClassifiers">
+                      <property name="text">
+                       <string>Display classification attribute names</string>
                       </property>
                      </widget>
                     </item>
@@ -5526,7 +5519,6 @@ The bigger the number, the faster zooming with the mouse wheel will be.</string>
   <tabstop>mLegendGrpBx</tabstop>
   <tabstop>cmbLegendDoubleClickAction</tabstop>
   <tabstop>cbxLegendClassifiers</tabstop>
-  <tabstop>cbxCreateRasterLegendIcons</tabstop>
   <tabstop>mLegendGraphicResolutionSpinBox</tabstop>
   <tabstop>mOptionsScrollArea_05</tabstop>
   <tabstop>mIdentifyGroupBox</tabstop>