suggest to fix topological mesh error when starting mesh editing

python/core/auto_generated/mesh/qgsmesheditor.sip.in

@@ -70,7 +70,22 @@ The caller takes ownership.
 
     QgsMeshEditingError initialize();
 %Docstring
-Initialize the mesh editor and return errors if the internal native mesh have topologic errors
+Initializes the mesh editor and returns first error if the internal native mesh has topological errors
+%End
+
+    QgsMeshEditingError initializeWithErrorsFix();
+%Docstring
+Initializes the mesh editor. If topological errors occur,tries to fix these errors
+and returns error if there is one that couldn't be fixed
+
+.. versionadded:: 3.28
+%End
+
+    bool fixError( const QgsMeshEditingError &error );
+%Docstring
+Tries to fix the topological ``error`` in the mesh. Returns ``False`` if the fix fails
+
+.. versionadded:: 3.28
 %End
 
     bool faceCanBeAdded( const QgsMeshFace &face );

python/core/auto_generated/mesh/qgsmeshlayer.sip.in

@@ -760,17 +760,33 @@ Returns the relative time (in milliseconds) of the dataset from the reference ti
 .. versionadded:: 3.16
 %End
 
-    bool startFrameEditing( const QgsCoordinateTransform &transform );
+ bool startFrameEditing( const QgsCoordinateTransform &transform );
 %Docstring
-Starts edition of the mesh frame. Coordinate ``transform`` used to initialize the triangular mesh if needed.
-This operation will disconnect the mesh layer from the data provider anf removes all existing dataset group
+Starts editing of the mesh frame. Coordinate ``transform`` used to initialize the triangular mesh if needed.
+This operation will disconnect the mesh layer from the data provider and removes all existing dataset group
 
 .. versionadded:: 3.22
+
+.. deprecated:: QGIS 3.28
+  use the version with :py:class:`QgsMeshEditingError` instead
+%End
+
+    bool startFrameEditing( const QgsCoordinateTransform &transform, QgsMeshEditingError &error /Out/, bool fixErrors );
+%Docstring
+Starts editing of the mesh frame. Coordinate ``transform`` used to initialize the triangular mesh if needed.
+This operation will disconnect the mesh layer from the data provider and removes all existing dataset group.
+Returns ``False`` if starting fails and the ``error`` that is the reason (No error, if the mesh is not editable or already in edit mode).
+
+If ``fixErrors`` is set to ``True``, errors will be attempted to be fixed.
+In that case returns ``False`` if there is an error that could not be fixed and the remaining ``error``.
+
+.. versionadded:: 3.28
 %End
 
+
     bool commitFrameEditing( const QgsCoordinateTransform &transform, bool continueEditing = true );
 %Docstring
-Commits edition of the mesh frame,
+Commits editing of the mesh frame,
 Rebuilds the triangular mesh and its spatial index with ``transform``,
 Continue editing with the same mesh editor if ``continueEditing`` is True
 
@@ -781,7 +797,7 @@ Continue editing with the same mesh editor if ``continueEditing`` is True
 
     bool rollBackFrameEditing( const QgsCoordinateTransform &transform, bool continueEditing = true );
 %Docstring
-Rolls Back edition of the mesh frame.
+Rolls Back editing of the mesh frame.
 Reload mesh from file, rebuilds the triangular mesh and its spatial index with ``transform``,
 Continue editing with the same mesh editor if ``continueEditing`` is ``True``
 
@@ -792,7 +808,7 @@ Continue editing with the same mesh editor if ``continueEditing`` is ``True``
 
     void stopFrameEditing( const QgsCoordinateTransform &transform );
 %Docstring
-Stops edition of the mesh, re-indexes the faces and vertices,
+Stops editing of the mesh, re-indexes the faces and vertices,
 rebuilds the triangular mesh and its spatial index with ``transform``,
 clean the undostack
 

src/app/qgisapp.cpp

@@ -10750,15 +10750,37 @@ bool QgisApp::toggleEditingMeshLayer( QgsMeshLayer *mlayer, bool allowCancel )
       }
     }
 
-    res = mlayer->startFrameEditing( transform );
-    mActionToggleEditing->setChecked( res );
+    QgsMeshEditingError error;
+    {
+      QgsTemporaryCursorOverride waitCursor( Qt::WaitCursor );
+      res = mlayer->startFrameEditing( transform, error, false );
+    }
 
     if ( !res )
     {
-      visibleMessageBar()->pushWarning(
-        tr( "Mesh editing" ),
-        tr( "Unable to start mesh editing for layer \"%1\"" ).arg( mlayer->name() ) );
+      if ( error.errorType != Qgis::MeshEditingErrorType::NoError )
+      {
+        if ( QMessageBox::question( this, tr( "Mesh Editing" ),
+                                    tr( "At least one topological error in the mesh prevents starting editing.\n"
+                                        "Some errors can be fixed by removing invalid elements.\n\n"
+                                        "Do you want to try to fix errors before starting editing?" ),
+                                    QMessageBox::Yes | QMessageBox::No, QMessageBox::Yes ) == QMessageBox::Yes )
+        {
+          QgsTemporaryCursorOverride waitCursor( Qt::WaitCursor );
+          res = mlayer->startFrameEditing( transform, error, true );
+        }
+      }
+
+      if ( !res )
+      {
+        visibleMessageBar()->pushWarning(
+          tr( "Mesh editing" ),
+          tr( "Unable to start mesh editing for layer \"%1\"" ).arg( mlayer->name() ) );
+      }
+
     }
+
+    mActionToggleEditing->setChecked( res );
   }
   else if ( mlayer->isModified() )
   {

src/core/mesh/qgsmesheditor.cpp

@@ -19,8 +19,6 @@
 #include "qgsmeshdataprovider.h"
 #include "qgstriangularmesh.h"
 #include "qgsmeshlayer.h"
-#include "qgsmeshlayerutils.h"
-#include "qgslogger.h"
 #include "qgsgeometryengine.h"
 #include "qgsmeshadvancedediting.h"
 #include "qgsgeometryutils.h"
@@ -65,11 +63,89 @@ QgsMeshEditingError QgsMeshEditor::initialize()
 {
   QgsMeshEditingError error;
   mTopologicalMesh = QgsTopologicalMesh::createTopologicalMesh( mMesh, mMaximumVerticesPerFace, error );
+
+  if ( error.errorType == Qgis::MeshEditingErrorType::NoError )
+  {
+    // we check for free vertices that could be included in face here
+    // because we need the spatial index of the triangular mesh
+    const QList<int> freeVertices = mTopologicalMesh.freeVerticesIndexes();
+    for ( int vi : freeVertices )
+    {
+      if ( mTriangularMesh->faceIndexForPoint_v2( mTriangularMesh->vertices().at( vi ) ) != -1 )
+      {
+        error = QgsMeshEditingError( Qgis::MeshEditingErrorType::InvalidVertex, vi );
+        break;
+      }
+    }
+  }
+
   mValidFacesCount = mMesh->faceCount();
   mValidVerticesCount = mMesh->vertexCount();
   return error;
 }
 
+QgsMeshEditingError QgsMeshEditor::initializeWithErrorsFix()
+{
+  QgsMeshEditingError lastError;
+
+  while ( true )
+  {
+    lastError = initialize();
+    if ( lastError.errorType == Qgis::MeshEditingErrorType::NoError )
+      break;
+
+    if ( !fixError( lastError ) )
+      break;
+
+    mTriangularMesh->update( mMesh );
+  };
+
+  return lastError;
+}
+
+bool QgsMeshEditor::fixError( const QgsMeshEditingError &error )
+{
+  switch ( error.errorType )
+  {
+    case Qgis::MeshEditingErrorType::NoError:
+      return true;
+      break;
+    case Qgis::MeshEditingErrorType::InvalidFace:
+    case Qgis::MeshEditingErrorType::TooManyVerticesInFace:
+    case Qgis::MeshEditingErrorType::FlatFace:
+    case Qgis::MeshEditingErrorType::ManifoldFace:
+      if ( error.elementIndex != -1 && error.elementIndex < mMesh->faceCount() )
+      {
+        mMesh->faces.removeAt( error.elementIndex );
+        return true;
+      }
+      return false;
+      break;
+    case Qgis::MeshEditingErrorType::InvalidVertex:
+    case Qgis::MeshEditingErrorType::UniqueSharedVertex:
+    {
+      auto faceIt = mMesh->faces.begin();
+      while ( faceIt != mMesh->faces.end() )
+      {
+        if ( faceIt->contains( error.elementIndex ) )
+          faceIt = mMesh->faces.erase( faceIt );
+        else
+          ++faceIt;
+      }
+
+      if ( error.elementIndex >= 0 && error.elementIndex < mMesh->vertexCount() )
+      {
+        mMesh->vertices[error.elementIndex] = QgsMeshVertex();
+        reindex( false );
+      }
+      return true;
+    }
+    break;
+  }
+
+  return false;
+}
+
 void QgsMeshEditor::resetTriangularMesh( QgsTriangularMesh *triangularMesh )
 {
   mTriangularMesh = triangularMesh;
@@ -986,10 +1062,12 @@ bool QgsMeshEditor::reindex( bool renumbering )
     if ( !mTopologicalMesh.renumber() )
       return false;
 
-    QgsMeshEditingError error = initialize();
+    QgsMeshEditingError error;
+    mTopologicalMesh = QgsTopologicalMesh::createTopologicalMesh( mMesh, mMaximumVerticesPerFace, error );
+    mValidFacesCount = mMesh->faceCount();
+    mValidVerticesCount = mMesh->vertexCount();
     return error.errorType == Qgis::MeshEditingErrorType::NoError;
   }
-
   else
     return true;
 }

src/core/mesh/qgsmesheditor.h

@@ -82,9 +82,24 @@ class CORE_EXPORT QgsMeshEditor : public QObject
      */
     QgsMeshDatasetGroup *createZValueDatasetGroup() SIP_TRANSFERBACK;
 
-    //! Initialize the mesh editor and return errors if the internal native mesh have topologic errors
+    //! Initializes the mesh editor and returns first error if the internal native mesh has topological errors
     QgsMeshEditingError initialize();
 
+    /**
+     * Initializes the mesh editor. If topological errors occur,tries to fix these errors
+     * and returns error if there is one that couldn't be fixed
+     *
+     *  \since QGIS 3.28
+     */
+    QgsMeshEditingError initializeWithErrorsFix();
+
+    /**
+     * Tries to fix the topological \a error in the mesh. Returns FALSE if the fix fails
+     *
+     * \since QGIS 3.28
+     */
+    bool fixError( const QgsMeshEditingError &error );
+
     //! Resets the triangular mesh
     void resetTriangularMesh( QgsTriangularMesh *triangularMesh ); SIP_SKIP
 

src/core/mesh/qgsmeshlayer.cpp

@@ -966,6 +966,12 @@ static QString detailsErrorMessage( const QgsMeshEditingError &error )
 }
 
 bool QgsMeshLayer::startFrameEditing( const QgsCoordinateTransform &transform )
+{
+  QgsMeshEditingError error;
+  return startFrameEditing( transform, error, false );
+}
+
+bool QgsMeshLayer::startFrameEditing( const QgsCoordinateTransform &transform, QgsMeshEditingError &error, bool fixErrors )
 {
   if ( !supportsEditing() )
   {
@@ -985,7 +991,13 @@ bool QgsMeshLayer::startFrameEditing( const QgsCoordinateTransform &transform )
 
   mMeshEditor = new QgsMeshEditor( this );
 
-  const QgsMeshEditingError error = mMeshEditor->initialize();
+  if ( fixErrors )
+  {
+    mRendererCache.reset(); // fixing errors could lead to remove faces/vertices
+    error = mMeshEditor->initializeWithErrorsFix();
+  }
+  else
+    error = mMeshEditor->initialize();
 
   if ( error.errorType != Qgis::MeshEditingErrorType::NoError )
   {

src/core/mesh/qgsmeshlayer.h

@@ -40,6 +40,7 @@ class QgsMesh3dAveragingMethod;
 class QgsMeshLayerTemporalProperties;
 class QgsMeshDatasetGroupStore;
 class QgsMeshEditor;
+class QgsMeshEditingError;
 class QgsMeshLayerElevationProperties;
 
 /**
@@ -774,15 +775,29 @@ class CORE_EXPORT QgsMeshLayer : public QgsMapLayer, public QgsAbstractProfileSo
     qint64 datasetRelativeTimeInMilliseconds( const QgsMeshDatasetIndex &index );
 
     /**
-    * Starts edition of the mesh frame. Coordinate \a transform used to initialize the triangular mesh if needed.
-    * This operation will disconnect the mesh layer from the data provider anf removes all existing dataset group
+    * Starts editing of the mesh frame. Coordinate \a transform used to initialize the triangular mesh if needed.
+    * This operation will disconnect the mesh layer from the data provider and removes all existing dataset group
     *
     * \since QGIS 3.22
+    * \deprecated since QGIS 3.28, use the version with QgsMeshEditingError instead
     */
-    bool startFrameEditing( const QgsCoordinateTransform &transform );
+    Q_DECL_DEPRECATED bool startFrameEditing( const QgsCoordinateTransform &transform );
 
     /**
-    * Commits edition of the mesh frame,
+    * Starts editing of the mesh frame. Coordinate \a transform used to initialize the triangular mesh if needed.
+    * This operation will disconnect the mesh layer from the data provider and removes all existing dataset group.
+    * Returns FALSE if starting fails and the \a error that is the reason (No error, if the mesh is not editable or already in edit mode).
+    *
+    * If \a fixErrors is set to TRUE, errors will be attempted to be fixed.
+    * In that case returns FALSE if there is an error that could not be fixed and the remaining \a error.
+    *
+    * \since QGIS 3.28
+    */
+    bool startFrameEditing( const QgsCoordinateTransform &transform, QgsMeshEditingError &error SIP_OUT, bool fixErrors );
+
+
+    /**
+    * Commits editing of the mesh frame,
     * Rebuilds the triangular mesh and its spatial index with \a transform,
     * Continue editing with the same mesh editor if \a continueEditing is True
     *
@@ -792,7 +807,7 @@ class CORE_EXPORT QgsMeshLayer : public QgsMapLayer, public QgsAbstractProfileSo
     bool commitFrameEditing( const QgsCoordinateTransform &transform, bool continueEditing = true );
 
     /**
-    * Rolls Back edition of the mesh frame.
+    * Rolls Back editing of the mesh frame.
     * Reload mesh from file, rebuilds the triangular mesh and its spatial index with \a transform,
     * Continue editing with the same mesh editor if \a continueEditing is TRUE
     *
@@ -802,7 +817,7 @@ class CORE_EXPORT QgsMeshLayer : public QgsMapLayer, public QgsAbstractProfileSo
     bool rollBackFrameEditing( const QgsCoordinateTransform &transform, bool continueEditing = true );
 
     /**
-    * Stops edition of the mesh, re-indexes the faces and vertices,
+    * Stops editing of the mesh, re-indexes the faces and vertices,
     * rebuilds the triangular mesh and its spatial index with \a transform,
     * clean the undostack
     *

src/core/mesh/qgstriangularmesh.cpp

@@ -254,6 +254,11 @@ bool QgsTriangularMesh::update( QgsMesh *nativeMesh, const QgsCoordinateTransfor
   return true;
 }
 
+bool QgsTriangularMesh::update( QgsMesh *nativeMesh )
+{
+  return update( nativeMesh, mCoordinateTransform );
+}
+
 void QgsTriangularMesh::finalizeTriangles()
 {
   mAverageTriangleSize = 0;

src/core/mesh/qgstriangularmesh.h

@@ -62,7 +62,19 @@ class CORE_EXPORT QgsTriangularMesh // TODO rename to QgsRendererMesh in QGIS 4
      * \param transform Transformation from layer CRS to destination (e.g. map) CRS. With invalid transform, it keeps the native mesh CRS
      * \returns TRUE if the mesh is effectivly updated, and FALSE if not
     */
-    bool update( QgsMesh *nativeMesh, const QgsCoordinateTransform &transform = QgsCoordinateTransform() );
+    bool update( QgsMesh *nativeMesh, const QgsCoordinateTransform &transform );
+
+    /**
+     * Constructs triangular mesh from layer's native mesh using the coordinate transform already set. Populates spatial index.
+     * \param nativeMesh QgsMesh to access native vertices and faces
+     *
+     * \returns TRUE if the mesh is effectivly updated, and FALSE if not
+     *
+     * \note if the coordinate transform is not already set, it uses the native mesh CRS
+     *
+     * \since QGIS 3.28
+    */
+    bool update( QgsMesh *nativeMesh );
 
     /**
      * Returns vertices in map coordinate system

tests/src/app/testqgsmaptooleditmesh.cpp

@@ -79,7 +79,9 @@ void TestQgsMapToolEditMesh::hoverElements()
   mCanvas->setDestinationCrs( wgs84Crs );
 
   QgsCoordinateTransform transform( meshLayerSimpleBox->crs(), mCanvas->mapSettings().destinationCrs(), QgsProject::instance() );
-  QVERIFY( meshLayerSimpleBox->startFrameEditing( transform ) );
+  QgsMeshEditingError error;
+  QVERIFY( meshLayerSimpleBox->startFrameEditing( transform, error, false ) );
+  QVERIFY( error.errorType == Qgis::MeshEditingErrorType::NoError );
 
   QgsRectangle extent( 3.31351393, 47.97489613, 3.31351792, 47.97508220 );
   mCanvas->setExtent( extent );
@@ -110,7 +112,9 @@ void TestQgsMapToolEditMesh::editMesh()
   QCOMPARE( meshLayerQuadFlower->datasetGroupCount(), 1 );
 
   const QgsCoordinateTransform transform;
-  meshLayerQuadFlower->startFrameEditing( transform );
+  QgsMeshEditingError error;
+  meshLayerQuadFlower->startFrameEditing( transform, error, false );
+  QVERIFY( error == QgsMeshEditingError() );
 
   mCanvas->setLayers( QList<QgsMapLayer *>() << meshLayerQuadFlower.get() );
   const double offsetInMapUnits = 15 * mCanvas->mapSettings().mapUnitsPerPixel();
@@ -138,7 +142,8 @@ void TestQgsMapToolEditMesh::editMesh()
 
   QVERIFY( !meshLayerQuadFlower->meshEditor() );
 
-  meshLayerQuadFlower->startFrameEditing( transform );
+  meshLayerQuadFlower->startFrameEditing( transform, error, false );
+  QVERIFY( error == QgsMeshEditingError() );
 
   QVERIFY( meshLayerQuadFlower->meshEditor() );
 

tests/src/core/testqgsmesheditor.cpp

@@ -48,6 +48,7 @@ class TestQgsMeshEditor : public QObject
     void cleanup() {} // will be called after every testfunction.
 
     void startStopEditing();
+    void startEditingWithErrors();
     void createTopologicMesh();
     void editTopologicMesh();
     void badTopologicMesh();
@@ -114,9 +115,10 @@ void TestQgsMeshEditor::startStopEditing()
   QCOMPARE( meta.name(), QStringLiteral( "Bed Elevation" ) );
 
   const QgsCoordinateTransform transform;
+  QgsMeshEditingError error;
 
-  QVERIFY( meshLayerQuadTriangle->startFrameEditing( transform ) );
-  QVERIFY( !meshLayerQuadTriangle->startFrameEditing( transform ) ); //mesh editing is already started
+  QVERIFY( meshLayerQuadTriangle->startFrameEditing( transform, error, false ) );
+  QVERIFY( !meshLayerQuadTriangle->startFrameEditing( transform, error, false ) ); //mesh editing is already started
 
   // Edition has started, dataset groups are removed ans replace by a virtual one that represent the Z value of vertices
   QCOMPARE( meshLayerQuadTriangle->datasetGroupCount(), 1 );
@@ -185,6 +187,72 @@ void TestQgsMeshEditor::startStopEditing()
   QCOMPARE( meshLayerQuadTriangle->meshFaceCount(), 2 );
 }
 
+void TestQgsMeshEditor::startEditingWithErrors()
+{
+  const QgsCoordinateTransform transform;
+
+  QString uri( mDataDir + QStringLiteral( "/with_flat_face.2dm" ) );
+  std::unique_ptr<QgsMeshLayer> mesh = std::make_unique<QgsMeshLayer>( uri, QStringLiteral( "With flat face" ), QStringLiteral( "mdal" ) );
+  QVERIFY( mesh->isValid() );
+  QCOMPARE( mesh->meshFaceCount(), 3 );
+  QCOMPARE( mesh->meshVertexCount(), 5 );
+
+  QgsMeshEditingError error;
+  QVERIFY( !mesh->startFrameEditing( transform, error, false ) );
+  QCOMPARE( error, QgsMeshEditingError( Qgis::MeshEditingErrorType::FlatFace, 2 ) );
+
+  QVERIFY( mesh->startFrameEditing( transform, error, true ) );
+  QCOMPARE( error, QgsMeshEditingError() );
+
+  QCOMPARE( mesh->meshFaceCount(), 2 );
+  QCOMPARE( mesh->meshVertexCount(), 5 );
+
+  uri = mDataDir + QStringLiteral( "/with_manifold_face.2dm" );
+  mesh = std::make_unique<QgsMeshLayer>( uri, QStringLiteral( "With manifold face" ), QStringLiteral( "mdal" ) );
+  QVERIFY( mesh->isValid() );
+  QCOMPARE( mesh->meshFaceCount(), 3 );
+  QCOMPARE( mesh->meshVertexCount(), 5 );
+
+  QVERIFY( !mesh->startFrameEditing( transform, error, false ) );
+  QCOMPARE( error, QgsMeshEditingError( Qgis::MeshEditingErrorType::ManifoldFace, 1 ) );
+
+  QVERIFY( mesh->startFrameEditing( transform, error, true ) );
+  QCOMPARE( error, QgsMeshEditingError() );
+
+  QCOMPARE( mesh->meshFaceCount(), 2 );
+  QCOMPARE( mesh->meshVertexCount(), 5 );
+
+  uri = mDataDir + QStringLiteral( "/with_free_vertex_in_mesh.2dm" );
+  mesh = std::make_unique<QgsMeshLayer>( uri, QStringLiteral( "With free vertex in mesh" ), QStringLiteral( "mdal" ) );
+  QVERIFY( mesh->isValid() );
+  QCOMPARE( mesh->meshFaceCount(), 2 );
+  QCOMPARE( mesh->meshVertexCount(), 6 );
+
+  QVERIFY( !mesh->startFrameEditing( transform, error, false ) );
+  QCOMPARE( error, QgsMeshEditingError( Qgis::MeshEditingErrorType::InvalidVertex, 5 ) );
+
+  QVERIFY( mesh->startFrameEditing( transform, error, true ) );
+  QCOMPARE( error, QgsMeshEditingError() );
+
+  QCOMPARE( mesh->meshFaceCount(), 2 );
+  QCOMPARE( mesh->meshVertexCount(), 5 );
+
+  uri = mDataDir + QStringLiteral( "/with_unique_shared_vertex.2dm" );
+  mesh = std::make_unique<QgsMeshLayer>( uri, QStringLiteral( "With unique shared vertex" ), QStringLiteral( "mdal" ) );
+  QVERIFY( mesh->isValid() );
+  QCOMPARE( mesh->meshFaceCount(), 3 );
+  QCOMPARE( mesh->meshVertexCount(), 7 );
+
+  QVERIFY( !mesh->startFrameEditing( transform, error, false ) );
+  QCOMPARE( error, QgsMeshEditingError( Qgis::MeshEditingErrorType::UniqueSharedVertex, 2 ) );
+
+  QVERIFY( mesh->startFrameEditing( transform, error, true ) );
+  QCOMPARE( error, QgsMeshEditingError() );
+
+  QCOMPARE( mesh->meshFaceCount(), 1 );
+  QCOMPARE( mesh->meshVertexCount(), 6 );
+}
+
 static bool checkNeighbors( const QgsTopologicalMesh &mesh, int faceIndex, const QList<int> &expectedNeighbors )
 {
   const QVector<int> neighbors = mesh.neighborsOfFace( faceIndex );
@@ -736,7 +804,8 @@ void TestQgsMeshEditor::meshEditorSimpleEdition()
   const QUndoStack undoStack;
 
   const QgsCoordinateTransform transform;
-  QVERIFY( meshLayerQuadTriangle->startFrameEditing( transform ) );
+  QgsMeshEditingError error;
+  QVERIFY( meshLayerQuadTriangle->startFrameEditing( transform, error, false ) );
 
   QgsMesh mesh;
   QgsTriangularMesh triangularMesh;
@@ -751,8 +820,6 @@ void TestQgsMeshEditor::meshEditorSimpleEdition()
                                           QgsPoint( 1.0, 0.0, 0.0 ), // 3
                                           QgsPoint( )} );            // 4
 
-  QgsMeshEditingError error;
-
   meshEditor.addVertices( vertices, 0.01 );
 
   for ( int i = 0; i < 5; ++i )
@@ -809,7 +876,8 @@ void TestQgsMeshEditor::meshEditorSimpleEdition()
 void TestQgsMeshEditor::faceIntersection()
 {
   const QgsCoordinateTransform transform;
-  QVERIFY( meshLayerQuadFlower->startFrameEditing( transform ) );
+  QgsMeshEditingError error;
+  QVERIFY( meshLayerQuadFlower->startFrameEditing( transform, error, false ) );
 
   QgsMeshEditor *editor = meshLayerQuadFlower->meshEditor();
   QVERIFY( editor );
@@ -1352,7 +1420,8 @@ void TestQgsMeshEditor::meshEditorFromMeshLayer_quadTriangle()
   QCOMPARE( meshLayerQuadTriangle->meshFaceCount(), 2 );
 
   const QgsCoordinateTransform transform;
-  QVERIFY( meshLayerQuadTriangle->startFrameEditing( transform ) );
+  QgsMeshEditingError error;
+  QVERIFY( meshLayerQuadTriangle->startFrameEditing( transform, error, false ) );
 
   QgsMeshEditor *editor = meshLayerQuadTriangle->meshEditor();
 
@@ -1402,7 +1471,7 @@ void TestQgsMeshEditor::meshEditorFromMeshLayer_quadTriangle()
   meshLayerQuadTriangle->undoStack()->undo();
 
   // try to add a face that shares only one vertex
-  QgsMeshEditingError error = editor->addFaces( {{2, 5, 6}} );
+  error = editor->addFaces( {{2, 5, 6}} );
   QVERIFY( error == QgsMeshEditingError( Qgis::MeshEditingErrorType::UniqueSharedVertex, 2 ) );
   QCOMPARE( meshLayerQuadTriangle->meshVertexCount(), 7 );
   QCOMPARE( meshLayerQuadTriangle->meshFaceCount(), 2 );
@@ -1685,15 +1754,14 @@ void TestQgsMeshEditor::meshEditorFromMeshLayer_quadFlower()
   QCOMPARE( meshLayerQuadFlower->meshFaceCount(), 5 );
 
   const QgsCoordinateTransform transform;
-  QVERIFY( meshLayerQuadFlower->startFrameEditing( transform ) );
+  QgsMeshEditingError error;
+  QVERIFY( meshLayerQuadFlower->startFrameEditing( transform, error, false ) );
 
   QgsMeshEditor *editor = meshLayerQuadFlower->meshEditor();
   QVERIFY( editor );
   editor->mMaximumVerticesPerFace = 5; //for testing
 
-  QgsMeshEditingError error;
-
-  meshLayerQuadFlower->startFrameEditing( transform );
+  meshLayerQuadFlower->startFrameEditing( transform, error, false );
   editor = meshLayerQuadFlower->meshEditor();
   QCOMPARE( editor->addPointsAsVertices( {QgsPoint( 1500, 2800, -10 )}, 10 ), 1 ); // 8
   QCOMPARE( meshLayerQuadFlower->meshFaceCount(), 8 );
@@ -2095,7 +2163,8 @@ void TestQgsMeshEditor::transformByExpression()
   std::unique_ptr<QgsMeshLayer> layer = std::make_unique<QgsMeshLayer>( mDataDir + "/quad_flower_to_edit.2dm", "mesh", "mdal" );
 
   const QgsCoordinateTransform transform;
-  layer->startFrameEditing( transform );
+  QgsMeshEditingError error;
+  layer->startFrameEditing( transform, error, false );
 
   QgsMeshTransformVerticesByExpression transformVertex;
 
@@ -2249,7 +2318,7 @@ void TestQgsMeshEditor::forceByLine()
 
   QVERIFY( meshLayer->isValid() );
   QgsCoordinateTransform transform;
-  QVERIFY( meshLayer->startFrameEditing( transform ) );
+  QVERIFY( meshLayer->startFrameEditing( transform, error, false ) );
 
   QVERIFY( meshLayer->meshEditor() );
 

tests/testdata/mesh/with_flat_face.2dm

@@ -0,0 +1,9 @@
+MESH2D      1000.000      2000.000    0.000000     200     300  1.000  1.000
+ND         1      1000.000      2000.000      20.000
+ND         2      2000.000      2000.000      30.000
+ND         3      3000.000      2000.000      40.000
+ND         4      2000.000      3000.000      50.000
+ND         5      1000.000      3000.000      10.000
+E4Q        1    1    2    4    5   1
+E3T        2    2    3    4    1
+E3T        3    1    2    3    1

tests/testdata/mesh/with_free_vertex_in_mesh.2dm

@@ -0,0 +1,10 @@
+MESH2D      1000.000      2000.000    0.000000     200     300  1.000  1.000
+ND         1      1000.000      2000.000      20.000
+ND         2      2000.000      2000.000      30.000
+ND         3      3000.000      2000.000      40.000
+ND         4      2000.000      3000.000      50.000
+ND         5      1000.000      3000.000      10.000
+ND         6      1500.000      2500.000      10.000
+E4Q        1    1    2    4    5   1
+E3T        3    2    3    4    1
+

tests/testdata/mesh/with_manifold_face.2dm

@@ -0,0 +1,10 @@
+MESH2D      1000.000      2000.000    0.000000     200     300  1.000  1.000
+ND         1      1000.000      2000.000      20.000
+ND         2      2000.000      2000.000      30.000
+ND         3      3000.000      2000.000      40.000
+ND         4      2000.000      3000.000      50.000
+ND         5      1000.000      3000.000      10.000
+E4Q        1    1    2    4    5   1
+E3T        2    2    4    5    1
+E3T        3    2    3    4    1
+

tests/testdata/mesh/with_unique_shared_vertex.2dm

@@ -0,0 +1,12 @@
+MESH2D      1000.000      2000.000    0.000000     200     300  1.000  1.000
+ND         1      1000.000      2000.000      20.000
+ND         2      2000.000      2000.000      30.000
+ND         3      3000.000      2000.000      40.000
+ND         4      2000.000      3000.000      50.000
+ND         5      1000.000      3000.000      10.000
+ND         6      4000.000      3000.000      10.000
+ND         7      4000.000      2000.000      10.000
+E4Q        1    1    2    4    5   1
+E3T        2    2    3    4    1
+E3T        3    3    6    7    1
+