[vector tile] Add pseudo-unique FIDs where none are given (fixes #36995)

Feature IDs are optional in MVT encoding, and some datasets do not include them. In QGIS we need FIDs for some functionality to work correctly, for example labeling ignores label features with duplicate FIDs.
qgis · Jun 11, 2020 · af2e50c · af2e50c
1 parent b2da49b
commit af2e50c
Showing 1 changed file with 15 additions and 1 deletion.
diff --git a/src/core/vectortile/qgsvectortilemvtdecoder.cpp b/src/core/vectortile/qgsvectortilemvtdecoder.cpp
@@ -111,7 +111,21 @@ QgsVectorTileFeatures QgsVectorTileMVTDecoder::layerFeatures( const QMap<QString
     {
       const ::vector_tile::Tile_Feature &feature = layer.features( featureNum );
 
-      QgsFeature f( layerFields, static_cast<QgsFeatureId>( feature.id() ) );
+      QgsFeatureId fid;
+      if ( feature.has_id() )
+        fid = static_cast<QgsFeatureId>( feature.id() );
+      else
+      {
+        // There is no assigned ID, but some parts of QGIS do not work correctly if all IDs are zero
+        // (e.g. labeling will not register two features with the same FID within a single layer),
+        // so let's generate some pseudo-unique FIDs to keep those bits happy
+        fid = featureNum;
+        fid |= ( layerNum & 0xff ) << 24;
+        fid |= ( static_cast<QgsFeatureId>( mTileID.row() ) & 0xff ) << 32;
+        fid |= ( static_cast<QgsFeatureId>( mTileID.column() ) & 0xff ) << 40;
+      }
+
+      QgsFeature f( layerFields, fid );
 
       //
       // parse attributes