Port bugfix from PR #3906 to service

Author: dmarteau

src/server/services/wms/qgswmsservertransitional.cpp

@@ -1592,26 +1592,32 @@ namespace QgsWms
 
     //Adapt width / height if the aspect ratio does not correspond with the BBOX.
     //Required by WMS spec. 1.3.
-    if ( useBbox )
+    QString version = mParameters.value( QStringLiteral( "VERSION" ), QStringLiteral( "1.3.0" ) );
+    if ( useBbox && version != QLatin1String( "1.1.1" ) )
     {
       bool bboxOk;
       QgsRectangle mapExtent = _parseBBOX( mParameters.value( "BBOX" ), bboxOk );
+      QString crs = mParameters.value( QStringLiteral( "CRS" ), mParameters.value( QStringLiteral( "SRS" ) ) );
+      if ( crs.compare( "CRS:84", Qt::CaseInsensitive ) == 0 )
+      {
+        crs = QString( "EPSG:4326" );
+        mapExtent.invert();
+      }
+      QgsCoordinateReferenceSystem outputCRS = QgsCoordinateReferenceSystem::fromOgcWmsCrs( crs );
+      if ( outputCRS.hasAxisInverted() )
+      {
+        mapExtent.invert();
+      }
       if ( bboxOk )
       {
         double mapWidthHeightRatio = mapExtent.width() / mapExtent.height();
         double imageWidthHeightRatio = ( double )width / ( double )height;
         if ( !qgsDoubleNear( mapWidthHeightRatio, imageWidthHeightRatio, 0.0001 ) )
         {
-          if ( mapWidthHeightRatio >= imageWidthHeightRatio )
-          {
-            //increase image height
-            height = width * mapWidthHeightRatio;
-          }
-          else
-          {
-            //increase image width
-            width = height / mapWidthHeightRatio;
-          }
+          // inspired by MapServer, mapdraw.c L115
+          double cellsize = ( mapExtent.width() / ( double )width ) * 0.5 + ( mapExtent.height() / ( double )height ) * 0.5;
+          width = mapExtent.width() / cellsize;
+          height = mapExtent.height() / cellsize;
         }
       }
     }