Fixes 16707, export of hairline results in a different visual thickness

Author: aaime

src/core/symbology-ng/qgssymbollayerutils.cpp

@@ -1845,7 +1845,14 @@ void QgsSymbolLayerUtils::lineToSld( QDomDocument &doc, QDomElement &element,
       element.appendChild( createSvgParameterElement( doc, QStringLiteral( "stroke-opacity" ), encodeSldAlpha( color.alpha() ) ) );
   }
   if ( width > 0 )
+  {
     element.appendChild( createSvgParameterElement( doc, QStringLiteral( "stroke-width" ), qgsDoubleToString( width ) ) );
+  }
+  else if ( width == 0 )
+  {
+    // hairline, yet not zero. it's actually painted in qgis
+    element.appendChild( createSvgParameterElement( doc, QStringLiteral( "stroke-width" ), QStringLiteral( "0.5" ) ) );
+  }
   if ( penJoinStyle )
     element.appendChild( createSvgParameterElement( doc, QStringLiteral( "stroke-linejoin" ), encodeSldLineJoinStyle( *penJoinStyle ) ) );
   if ( penCapStyle )

tests/src/python/test_qgssymbollayer_createsld.py

@@ -231,6 +231,15 @@ def testEllipseMarkerUnitPixel(self):
         self.assertStrokeWidth(root, 2, 1)
         self.assertStaticDisplacement(root, 5, 10)
 
+    def testSimpleLineHairline(self):
+        symbol = QgsSimpleLineSymbolLayer(QColor("black"), 0)
+        dom, root = self.symbolToSld(symbol)
+
+        # print ("Simple line px: \n" + dom.toString())
+
+        # Hairline is turned into 0.5px
+        self.assertStrokeWidth(root, 1, 0.5)
+
     def testSimpleLineUnitDefault(self):
         symbol = QgsSimpleLineSymbolLayer(QColor("black"), 1)
         symbol.setCustomDashVector([10, 10])

tests/testdata/qgis_server/getstyles.txt

@@ -19,6 +19,7 @@ Content-Type: text/xml; charset=utf-8
         </se:Fill>
         <se:Stroke>
          <se:SvgParameter name="stroke">#000000</se:SvgParameter>
+         <se:SvgParameter name="stroke-width">0.5</se:SvgParameter>
         </se:Stroke>
        </se:Mark>
        <se:Size>7</se:Size>