Inverted polygon renderer: add an option to preprocess polygons using an union

Author: Hugo Mercier

src/core/symbology-ng/qgsinvertedpolygonrenderer.cpp

@@ -28,7 +28,7 @@
 #include <QDomElement>
 
 QgsInvertedPolygonRenderer::QgsInvertedPolygonRenderer( const QgsFeatureRendererV2* subRenderer )
-  : QgsFeatureRendererV2( "invertedPolygonRenderer" )
+  : QgsFeatureRendererV2( "invertedPolygonRenderer" ), mPreprocessingEnabled( false )
 {
   if ( subRenderer ) {
     setEmbeddedRenderer( subRenderer );
@@ -154,15 +154,6 @@ bool QgsInvertedPolygonRenderer::renderFeature( QgsFeature& feature, QgsRenderCo
     return false;
   }
 
-  // We build here a "reversed" geometry of all the polygons
-  //
-  // The final geometry is a multipolygon F, with :
-  // * the first polygon of F having the current extent as its exterior ring
-  // * each polygon's exterior ring is added as interior ring of the first polygon of F
-  // * each polygon's interior ring is added as new polygons in F
-  //
-  // No validity check is done, on purpose, it will be very slow and painting
-  // operations do not need geometries to be valid
   if ( ! mFeaturesCategoryMap.contains(catId) )
   {
     // the exterior ring must be a square in the destination CRS
@@ -173,7 +164,7 @@ bool QgsInvertedPolygonRenderer::renderFeature( QgsFeature& feature, QgsRenderCo
     mFeaturesCategoryMap.insert( catId, cFeat );
   }
 
-  // update the gometry
+  // update the geometry
   CombinedFeature& cFeat = mFeaturesCategoryMap[catId];
   QgsMultiPolygon multi;
   QgsGeometry* geom = feature.geometry();
@@ -190,37 +181,69 @@ bool QgsInvertedPolygonRenderer::renderFeature( QgsFeature& feature, QgsRenderCo
     multi = geom->asMultiPolygon();
   }
 
-  for ( int i = 0; i < multi.size(); i++ ) {
-    // add the exterior ring as interior ring to the first polygon
-    if ( mTransform ) {
-      QgsPolyline new_ls;
-      QgsPolyline& old_ls = multi[i][0];
-      for ( int k = 0; k < old_ls.size(); k++ ) {
-        new_ls.append( mTransform->transform( old_ls[k] ) );
-      }
-      cFeat.multiPolygon[0].append( new_ls );
+  if ( mPreprocessingEnabled )
+  {
+    // preprocessing
+    if ( ! cFeat.feature.geometry() )
+    {
+      // first feature: add the current geometry
+      cFeat.feature.setGeometry( new QgsGeometry(*geom) );
     }
     else
     {
-      cFeat.multiPolygon[0].append( multi[i][0] );
+      // other features: combine them (union)
+      QgsGeometry* combined = cFeat.feature.geometry()->combine( geom );
+      if ( combined && combined->isGeosValid() )
+      {
+        cFeat.feature.setGeometry( combined );
+      }
     }
-    // add interior rings as new polygons
-    for ( int j = 1; j < multi[i].size(); j++ ) {
-      QgsPolygon new_poly;
+  }
+  else
+  {
+    // No preprocessing involved.
+    // We build here a "reversed" geometry of all the polygons
+    //
+    // The final geometry is a multipolygon F, with :
+    // * the first polygon of F having the current extent as its exterior ring
+    // * each polygon's exterior ring is added as interior ring of the first polygon of F
+    // * each polygon's interior ring is added as new polygons in F
+    //
+    // No validity check is done, on purpose, it will be very slow and painting
+    // operations do not need geometries to be valid
+
+    for ( int i = 0; i < multi.size(); i++ ) {
+      // add the exterior ring as interior ring to the first polygon
       if ( mTransform ) {
         QgsPolyline new_ls;
-        QgsPolyline& old_ls = multi[i][j];
+        QgsPolyline& old_ls = multi[i][0];
         for ( int k = 0; k < old_ls.size(); k++ ) {
           new_ls.append( mTransform->transform( old_ls[k] ) );
         }
-        new_poly.append( new_ls );
+        cFeat.multiPolygon[0].append( new_ls );
       }
       else
       {
-        new_poly.append( multi[i][j] );
+        cFeat.multiPolygon[0].append( multi[i][0] );
       }
+      // add interior rings as new polygons
+      for ( int j = 1; j < multi[i].size(); j++ ) {
+        QgsPolygon new_poly;
+        if ( mTransform ) {
+          QgsPolyline new_ls;
+          QgsPolyline& old_ls = multi[i][j];
+          for ( int k = 0; k < old_ls.size(); k++ ) {
+            new_ls.append( mTransform->transform( old_ls[k] ) );
+          }
+          new_poly.append( new_ls );
+        }
+        else
+        {
+          new_poly.append( multi[i][j] );
+        }
 
-      cFeat.multiPolygon.append( new_poly );
+        cFeat.multiPolygon.append( new_poly );
+      }
     }
   }
   return true;
@@ -239,7 +262,24 @@ void QgsInvertedPolygonRenderer::stopRender( QgsRenderContext& context )
   for ( FeatureCategoryMap::iterator cit = mFeaturesCategoryMap.begin(); cit != mFeaturesCategoryMap.end(); ++cit)
   {
     QgsFeature feat( cit.value().feature );
-    feat.setGeometry( QgsGeometry::fromMultiPolygon( cit.value().multiPolygon ) );
+    if ( !mPreprocessingEnabled )
+    {
+      // no preprocessing - the final polygon has already been prepared
+      feat.setGeometry( QgsGeometry::fromMultiPolygon( cit.value().multiPolygon ) );
+    }
+    else
+    {
+      // preprocessing mode - we still have to invert (using difference)
+      if ( feat.geometry() )
+      {
+        QScopedPointer<QgsGeometry> rect( QgsGeometry::fromPolygon( mExtentPolygon ) );
+        QgsGeometry *final = rect->difference( feat.geometry() );
+        if ( final )
+        {
+          feat.setGeometry( final );
+        }
+      }
+    }
     mSubRenderer->renderFeature( feat, context );
   }
 
@@ -280,12 +320,17 @@ QString QgsInvertedPolygonRenderer::dump() const
 
 QgsFeatureRendererV2* QgsInvertedPolygonRenderer::clone()
 {
+  QgsInvertedPolygonRenderer* newRenderer;
   if ( mSubRenderer.isNull() )
   {
-    return new QgsInvertedPolygonRenderer( 0 );
+    newRenderer = new QgsInvertedPolygonRenderer( 0 );
+  }
+  else
+  {
+    newRenderer = new QgsInvertedPolygonRenderer( mSubRenderer->clone() );
   }
-  // else
-  return new QgsInvertedPolygonRenderer( mSubRenderer->clone() );
+  newRenderer->setPreprocessingEnabled( preprocessingEnabled() );
+  return newRenderer;
 }
 
 QgsFeatureRendererV2* QgsInvertedPolygonRenderer::create( QDomElement& element )
@@ -297,13 +342,15 @@ QgsFeatureRendererV2* QgsInvertedPolygonRenderer::create( QDomElement& element )
   {
     r->setEmbeddedRenderer( QgsFeatureRendererV2::load( embeddedRendererElem ) );
   }
+  r->setPreprocessingEnabled( element.attribute( "preprocessing", "0" ).toInt() == 1 );
   return r;
 }
 
 QDomElement QgsInvertedPolygonRenderer::save( QDomDocument& doc )
 {
   QDomElement rendererElem = doc.createElement( RENDERER_TAG_NAME );
   rendererElem.setAttribute( "type", "invertedPolygonRenderer" );
+  rendererElem.setAttribute( "preprocessing", preprocessingEnabled() ? "1" : "0" );
 
   if ( mSubRenderer )
   {

src/core/symbology-ng/qgsinvertedpolygonrenderer.h

@@ -104,6 +104,16 @@ class CORE_EXPORT QgsInvertedPolygonRenderer : public QgsFeatureRendererV2
    */
   const QgsFeatureRendererV2* embeddedRenderer() const;
 
+  /** @returns true if the geometries are to be preprocessed (merged with an union) before rendering.*/
+  bool preprocessingEnabled() const { return mPreprocessingEnabled; }
+  /** 
+      @param enabled enables or disables the preprocessing.
+      When enabled, geometries will be merged with an union before being rendered.
+      It allows to fix some rendering artefacts (when rendering overlapping polygons for instance).
+      This will involve some CPU-demanding computations and is thus disabled by default.
+  */
+  void setPreprocessingEnabled( bool enabled ) { mPreprocessingEnabled = enabled; }
+
  private:
   /** Private copy constructor. @see clone() */
   QgsInvertedPolygonRenderer( const QgsInvertedPolygonRenderer& );
@@ -145,6 +155,9 @@ class CORE_EXPORT QgsInvertedPolygonRenderer : public QgsFeatureRendererV2
     feature(a_feature),selected(a_selected), drawMarkers(a_drawMarkers), layer(a_layer) {}
   };
   QList<FeatureDecoration> mFeatureDecorations;
+
+  /** whether to preprocess (merge) geometries before rendering*/
+  bool mPreprocessingEnabled;
 };
 
 

src/gui/symbology-ng/qgsinvertedpolygonrendererwidget.cpp

@@ -67,6 +67,9 @@ QgsInvertedPolygonRendererWidget::QgsInvertedPolygonRendererWidget( QgsVectorLay
   {
     // an existing inverted renderer
     mRenderer.reset( static_cast<QgsInvertedPolygonRenderer*>(renderer) );
+    mMergePolygonsCheckBox->blockSignals( true );
+    mMergePolygonsCheckBox->setCheckState( mRenderer->preprocessingEnabled() ? Qt::Checked : Qt::Unchecked );
+    mMergePolygonsCheckBox->blockSignals( false );
   }
 
   int currentEmbeddedIdx = 0;
@@ -122,11 +125,15 @@ void QgsInvertedPolygonRendererWidget::on_mRendererComboBox_currentIndexChanged(
   {
     mEmbeddedRendererWidget.reset( m->createRendererWidget( mLayer, mStyle, const_cast<QgsFeatureRendererV2*>(mRenderer->embeddedRenderer())->clone() ) );
 
-    if ( mLayout->count() > 1 ) {
+    if ( mLayout->count() > 2 ) {
       // remove the current renderer widget
-      mLayout->takeAt( 1 );
+      mLayout->takeAt( 2 );
     }
     mLayout->addWidget( mEmbeddedRendererWidget.data() );
   }
 }
 
+void QgsInvertedPolygonRendererWidget::on_mMergePolygonsCheckBox_stateChanged( int state )
+{
+  mRenderer->setPreprocessingEnabled( state == Qt::Checked );
+}

src/gui/symbology-ng/qgsinvertedpolygonrendererwidget.h

@@ -54,6 +54,7 @@ class GUI_EXPORT QgsInvertedPolygonRendererWidget : public QgsRendererV2Widget,
 
  private slots:
   void on_mRendererComboBox_currentIndexChanged( int index );
+  void on_mMergePolygonsCheckBox_stateChanged( int state );
 };
 
 

src/ui/qgsinvertedpolygonrendererwidgetbase.ui

@@ -6,8 +6,8 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>390</width>
-    <height>79</height>
+    <width>316</width>
+    <height>75</height>
    </rect>
   </property>
   <property name="windowTitle">
@@ -28,6 +28,16 @@
      </item>
     </layout>
    </item>
+   <item>
+    <widget class="QCheckBox" name="mMergePolygonsCheckBox">
+     <property name="toolTip">
+      <string/>
+     </property>
+     <property name="text">
+      <string>Merge polygons before rendering (slow)</string>
+     </property>
+    </widget>
+   </item>
   </layout>
  </widget>
  <resources/>

tests/src/core/testqgsinvertedpolygonrenderer.cpp

@@ -47,6 +47,7 @@ class TestQgsInvertedPolygon: public QObject
 
     void singleSubRenderer();
     void graduatedSubRenderer();
+    void preprocess();
 
   private:
     bool mTestHasError;
@@ -73,7 +74,7 @@ void TestQgsInvertedPolygon::initTestCase()
   //
   //create a poly layer that will be used in all tests...
   //
-  QString myPolysFileName = mTestDataDir + "polys.shp";
+  QString myPolysFileName = mTestDataDir + "polys_overlapping.shp";
   QFileInfo myPolyFileInfo( myPolysFileName );
   mpPolysLayer = new QgsVectorLayer( myPolyFileInfo.filePath(),
                                      myPolyFileInfo.completeBaseName(), "ogr" );
@@ -115,6 +116,14 @@ void TestQgsInvertedPolygon::graduatedSubRenderer()
   QVERIFY( imageCheck( "inverted_polys_graduated" ) );
 }
 
+void TestQgsInvertedPolygon::preprocess()
+{
+  // FIXME will have to find some overlapping polygons
+  mReport += "<h2>Inverted polygon renderer, preprocessing test</h2>\n";  
+  QVERIFY( setQml( "inverted_polys_preprocess.qml" ) );
+  QVERIFY( imageCheck( "inverted_polys_preprocess" ) );
+}
+
 //
 // Private helper functions not called directly by CTest
 //

tests/testdata/control_images/expected_inverted_polys_graduated/expected_inverted_polys_graduated.png

@@ -1,7 +1,7 @@
 <!DOCTYPE qgis PUBLIC 'http://mrcc.com/qgis.dtd' 'SYSTEM'>
 <qgis version="2.3.0-Master" minimumScale="1" maximumScale="1e+08" simplifyDrawingHints="1" minLabelScale="1" maxLabelScale="1e+08" simplifyDrawingTol="1" simplifyMaxScale="1" hasScaleBasedVisibilityFlag="0" simplifyLocal="1" scaleBasedLabelVisibilityFlag="0">
-  <renderer-v2 type="invertedPolygonRenderer">
-    <renderer-v2 attr="Name" symbollevels="0" type="categorizedSymbol">
+  <renderer-v2 preprocessing="0" type="invertedPolygonRenderer">
+    <renderer-v2 attr="Name" symbollevels="1" type="categorizedSymbol">
       <categories>
         <category symbol="0" value="Dam" label="Dam"/>
         <category symbol="1" value="Lake" label="Lake"/>
@@ -27,7 +27,7 @@
           </layer>
         </symbol>
         <symbol alpha="1" type="fill" name="1">
-          <layer pass="0" class="ShapeburstFill" locked="0">
+          <layer pass="1" class="ShapeburstFill" locked="0">
             <prop k="blur_radius" v="0"/>
             <prop k="color1" v="0,0,255,255"/>
             <prop k="color2" v="0,255,0,255"/>