Gracefully handle transform errors in snap to grid

Author: m-kuhn

src/gui/qgsmapmouseevent.cpp

@@ -76,16 +76,23 @@ void QgsMapMouseEvent::snapToGrid( double precision, const QgsCoordinateReferenc
   if ( precision <= 0 )
     return;
 
-  QgsCoordinateTransform ct( mMapCanvas->mapSettings().destinationCrs(), crs, mMapCanvas->mapSettings().transformContext() );
+  try
+  {
+    QgsCoordinateTransform ct( mMapCanvas->mapSettings().destinationCrs(), crs, mMapCanvas->mapSettings().transformContext() );
 
-  QgsPointXY pt = ct.transform( mMapPoint );
+    QgsPointXY pt = ct.transform( mMapPoint );
 
-  pt.setX( std::round( pt.x() / precision ) * precision );
-  pt.setY( std::round( pt.y() / precision ) * precision );
+    pt.setX( std::round( pt.x() / precision ) * precision );
+    pt.setY( std::round( pt.y() / precision ) * precision );
 
-  pt = ct.transform( pt, QgsCoordinateTransform::ReverseTransform );
+    pt = ct.transform( pt, QgsCoordinateTransform::ReverseTransform );
 
-  setMapPoint( pt );
+    setMapPoint( pt );
+  }
+  catch ( QgsCsException &e )
+  {
+    Q_UNUSED( e )
+  }
 }
 
 QPoint QgsMapMouseEvent::mapToPixelCoordinates( const QgsPointXY &point )

src/gui/qgssnaptogridcanvasitem.cpp

@@ -38,33 +38,42 @@ void QgsSnapToGridCanvasItem::paint( QPainter *painter )
 
   if ( mEnabled && mAvailableByZoomFactor )
   {
-    const QgsRectangle layerExtent = mTransform.transformBoundingBox( mapRect, QgsCoordinateTransform::ReverseTransform );
-    const QgsPointXY layerPt = mTransform.transform( mPoint, QgsCoordinateTransform::ReverseTransform );
+    try
+    {
+      const QgsRectangle layerExtent = mTransform.transformBoundingBox( mapRect, QgsCoordinateTransform::ReverseTransform );
+      const QgsPointXY layerPt = mTransform.transform( mPoint, QgsCoordinateTransform::ReverseTransform );
 
-    const double gridXMin = std::ceil( layerExtent.xMinimum() / mPrecision ) * mPrecision;
-    const double gridXMax = std::ceil( layerExtent.xMaximum() / mPrecision ) * mPrecision;
-    const double gridYMin = std::ceil( layerExtent.yMinimum() / mPrecision ) * mPrecision;
-    const double gridYMax = std::ceil( layerExtent.yMaximum() / mPrecision ) * mPrecision;
+      const double gridXMin = std::ceil( layerExtent.xMinimum() / mPrecision ) * mPrecision;
+      const double gridXMax = std::ceil( layerExtent.xMaximum() / mPrecision ) * mPrecision;
+      const double gridYMin = std::ceil( layerExtent.yMinimum() / mPrecision ) * mPrecision;
+      const double gridYMax = std::ceil( layerExtent.yMaximum() / mPrecision ) * mPrecision;
 
-    for ( int x = gridXMin ; x < gridXMax; x += mPrecision )
-    {
-      for ( int y = gridYMin ; y < gridYMax; y += mPrecision )
+      for ( int x = gridXMin ; x < gridXMax; x += mPrecision )
       {
-        const QgsPointXY pt = mTransform.transform( x, y );
-        const QPointF canvasPt = toCanvasCoordinates( pt );
-
-        if ( qgsDoubleNear( layerPt.x(), x, mPrecision / 3 ) && qgsDoubleNear( layerPt.y(), y, mPrecision / 3 ) )
-        {
-          painter->setPen( mCurrentPointPen );
-        }
-        else
+        for ( int y = gridYMin ; y < gridYMax; y += mPrecision )
         {
-          painter->setPen( mGridPen );
+          const QgsPointXY pt = mTransform.transform( x, y );
+          const QPointF canvasPt = toCanvasCoordinates( pt );
+
+          if ( qgsDoubleNear( layerPt.x(), x, mPrecision / 3 ) && qgsDoubleNear( layerPt.y(), y, mPrecision / 3 ) )
+          {
+            painter->setPen( mCurrentPointPen );
+          }
+          else
+          {
+            painter->setPen( mGridPen );
+          }
+          painter->drawLine( canvasPt.x() - 3, canvasPt.y(), canvasPt.x() + 3, canvasPt.y() );
+          painter->drawLine( canvasPt.x(), canvasPt.y() - 3, canvasPt.x(), canvasPt.y() + 3 );
+
         }
-        painter->drawLine( canvasPt.x() - 3, canvasPt.y(), canvasPt.x() + 3, canvasPt.y() );
-        painter->drawLine( canvasPt.x(), canvasPt.y() - 3, canvasPt.x(), canvasPt.y() + 3 );
       }
     }
+    catch ( QgsCsException &e )
+    {
+      Q_UNUSED( e )
+      mAvailableByZoomFactor = false;
+    }
   }
 
   painter->restore();