Refactor QgsTessellator so that errors are stored

Instead of writing errors to QgsMessageLog and discarding, instead
make the QgsTessellator class store errors and make the callers
responsible for pushing to QgsMessageLog when appropriate.

Gives us more flexibility to show user facing tesselation errors,
eg in the processing log.

python/PyQt6/core/auto_generated/qgstessellator.sip.in

@@ -80,6 +80,13 @@ Returns minimal Z value of the data (in world coordinates)
 Returns maximal Z value of the data (in world coordinates)
 
 .. versionadded:: 3.12
+%End
+
+    QString error() const;
+%Docstring
+Returns a descriptive error string if the tessellation failed.
+
+.. versionadded:: 3.34
 %End
 
 };

python/core/auto_generated/qgstessellator.sip.in

@@ -80,6 +80,13 @@ Returns minimal Z value of the data (in world coordinates)
 Returns maximal Z value of the data (in world coordinates)
 
 .. versionadded:: 3.12
+%End
+
+    QString error() const;
+%Docstring
+Returns a descriptive error string if the tessellation failed.
+
+.. versionadded:: 3.34
 %End
 
 };

src/3d/qgstessellatedpolygongeometry.cpp

@@ -15,6 +15,8 @@
 
 #include "qgstessellatedpolygongeometry.h"
 #include "qgsraycastingutils_p.h"
+#include "qgsmessagelog.h"
+
 #include <QMatrix4x4>
 
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
@@ -98,6 +100,10 @@ void QgsTessellatedPolygonGeometry::setPolygons( const QList<QgsPolygon *> &poly
     const float extr = extrusionHeightPerPolygon.isEmpty() ? extrusionHeight : extrusionHeightPerPolygon.at( i );
     tessellator.addPolygon( *polygon, extr );
   }
+  if ( !tessellator.error().isEmpty() )
+  {
+    QgsMessageLog::logMessage( tessellator.error(), QObject::tr( "3D" ) );
+  }
 
   qDeleteAll( polygons );
 

src/3d/symbols/qgsline3dsymbol_p.cpp

@@ -31,6 +31,7 @@
 #include "qgssimplelinematerialsettings.h"
 #include "qgspolygon.h"
 #include "qgsphongtexturedmaterialsettings.h"
+#include "qgsmessagelog.h"
 
 #include <Qt3DExtras/QPhongMaterial>
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
@@ -174,6 +175,11 @@ void QgsBufferedLine3DSymbolHandler::processPolygon( QgsPolygon *polyBuffered, Q
   out.triangleIndexStartingIndices.append( startingTriangleIndex );
   out.triangleIndexFids.append( fid );
   out.tessellator->addPolygon( *polyBuffered, extrusionHeight );
+  if ( !out.tessellator->error().isEmpty() )
+  {
+    QgsMessageLog::logMessage( out.tessellator->error(), QObject::tr( "3D" ) );
+  }
+
   delete polyBuffered;
 }
 

src/3d/symbols/qgspolygon3dsymbol_p.cpp

@@ -39,6 +39,7 @@
 #include "qgslinestring.h"
 #include "qgsmultipolygon.h"
 #include "qgspolygon.h"
+#include "qgsmessagelog.h"
 
 #include "qgslinevertexdata_p.h"
 #include "qgslinematerial_p.h"
@@ -144,6 +145,10 @@ void QgsPolygon3DSymbolHandler::processPolygon( const QgsPolygon *poly, QgsFeatu
   out.triangleIndexStartingIndices.append( startingTriangleIndex );
   out.triangleIndexFids.append( fid );
   out.tessellator->addPolygon( *polyClone, extrusionHeight );
+  if ( !out.tessellator->error().isEmpty() )
+  {
+    QgsMessageLog::logMessage( out.tessellator->error(), QObject::tr( "3D" ) );
+  }
 
   if ( mSymbol->materialSettings()->dataDefinedProperties().hasActiveProperties() )
     processMaterialDatadefined( out.tessellator->dataVerticesCount() - oldVerticesCount, context.expressionContext(), out );

src/core/qgstessellator.cpp

@@ -18,7 +18,6 @@
 #include "qgscurve.h"
 #include "qgsgeometryutils_base.h"
 #include "qgsgeometry.h"
-#include "qgsmessagelog.h"
 #include "qgsmultipolygon.h"
 #include "qgspoint.h"
 #include "qgspolygon.h"
@@ -615,7 +614,7 @@ void QgsTessellator::addPolygon( const QgsPolygon &polygon, float extrusionHeigh
       const QgsGeometry polygonSimplified = QgsGeometry( polygonNew->clone() ).simplify( 0.001 );
       if ( polygonSimplified.isNull() )
       {
-        QgsMessageLog::logMessage( QObject::tr( "geometry simplification failed - skipping" ), QObject::tr( "3D" ) );
+        mError = QObject::tr( "geometry simplification failed - skipping" );
         return;
       }
       const QgsPolygon *polygonSimplifiedData = qgsgeometry_cast<const QgsPolygon *>( polygonSimplified.constGet() );
@@ -623,7 +622,7 @@ void QgsTessellator::addPolygon( const QgsPolygon &polygon, float extrusionHeigh
       {
         // Failed to fix that. It could be a really tiny geometry... or maybe they gave us
         // geometry in unprojected lat/lon coordinates
-        QgsMessageLog::logMessage( QObject::tr( "geometry's coordinates are too close to each other and simplification failed - skipping" ), QObject::tr( "3D" ) );
+        mError = QObject::tr( "geometry's coordinates are too close to each other and simplification failed - skipping" );
         return;
       }
       else
@@ -716,9 +715,13 @@ void QgsTessellator::addPolygon( const QgsPolygon &polygon, float extrusionHeigh
         }
       }
     }
+    catch ( std::runtime_error &err )
+    {
+      mError = err.what();
+    }
     catch ( ... )
     {
-      QgsMessageLog::logMessage( QObject::tr( "Triangulation failed. Skipping polygon…" ), QObject::tr( "3D" ) );
+      mError = QObject::tr( "An unknown error occurred" );
     }
 
     for ( int i = 0; i < polylinesToDelete.count(); ++i )

src/core/qgstessellator.h

@@ -89,6 +89,13 @@ class CORE_EXPORT QgsTessellator
      */
     float zMaximum() const { return mZMax; }
 
+    /**
+     * Returns a descriptive error string if the tessellation failed.
+     *
+     * \since QGIS 3.34
+     */
+    QString error() const { return mError; }
+
   private:
     void init();
 
@@ -103,6 +110,7 @@ class CORE_EXPORT QgsTessellator
     bool mNoZ = false;
     int mTessellatedFacade = 3;
     float mTextureRotation = 0.0f;
+    QString mError;
 
     float mZMin = std::numeric_limits<float>::max();
     float mZMax = -std::numeric_limits<float>::max();