[labeling] Fix SLD export of negative offset

Fix #58862

src/core/labeling/qgsvectorlayerlabeling.cpp

@@ -348,7 +348,7 @@ void QgsAbstractVectorLayerLabeling::writeTextSymbolizer( QDomNode &parent, QgsP
       const QPointF anchor = quadOffsetToSldAnchor( settings.pointSettings().quadrant() );
       QgsSymbolLayerUtils::createAnchorPointElement( doc, pointPlacement, anchor );
       // displacement
-      if ( settings.xOffset > 0 || settings.yOffset > 0 )
+      if ( settings.xOffset != 0 || settings.yOffset != 0 )
       {
         const Qgis::RenderUnit offsetUnit =  settings.offsetUnits;
         const double dx = QgsSymbolLayerUtils::rescaleUom( settings.xOffset, offsetUnit, props );

tests/src/python/test_qgsserver_wms.py

@@ -27,9 +27,22 @@
 import osgeo.gdal  # NOQA
 
 from owslib.wms import WebMapService
-from qgis.core import QgsProject
-from qgis.PyQt.QtCore import QUrl
-from qgis.server import QgsBufferServerResponse, QgsServer, QgsServerRequest
+from qgis.core import (
+    QgsProject,
+    QgsMemoryProviderUtils,
+    QgsWkbTypes,
+    QgsCoordinateReferenceSystem,
+    QgsFields,
+    QgsField,
+    QgsPalLayerSettings,
+    QgsVectorLayerSimpleLabeling,
+)
+from qgis.PyQt.QtCore import QUrl, QUrlQuery, QVariant
+from qgis.server import (
+    QgsBufferServerResponse,
+    QgsServer,
+    QgsServerRequest,
+)
 from qgis.testing import unittest
 from test_qgsserver import QgsServerTestBase
 
@@ -420,6 +433,37 @@ def test_getcapabilities_owslib(self):
         rootLayerName = 'QGIS Test Project'
         self.assertIn(rootLayerName, w.contents.keys())
 
+    def test_get_styles_sld_label_negative_offset(self):
+        """Test issue GH #458862"""
+
+        # Create a point layer with a negative offset for the label
+        project = QgsProject()
+        fields = QgsFields()
+        fields.append(QgsField('int', QVariant.Int))
+        layer = QgsMemoryProviderUtils.createMemoryLayer('pointlabel', fields, QgsWkbTypes.Point, QgsCoordinateReferenceSystem(4326))
+        layer.setLabelsEnabled(True)
+        settings = QgsPalLayerSettings()
+        settings.xOffset = -10
+        settings.yOffset = -5
+        settings.fieldName = 'int'
+        settings.enabled = True
+        settings.placement = QgsPalLayerSettings.Placement.OverPoint
+
+        labeling = QgsVectorLayerSimpleLabeling(settings)
+        layer.setLabeling(labeling)
+
+        project.addMapLayer(layer)
+
+        # Test GetStyles with labeling
+        server = QgsServer()
+        request = QgsServerRequest()
+        request.setUrl(QUrl('?SERVICE=WMS&REQUEST=GetStyles&LAYERS=pointlabel'))
+        response = QgsBufferServerResponse()
+        server.handleRequest(request, response, project)
+        body = response.body().data().decode('utf8').replace('\n', '')
+        self.assertIn('<se:DisplacementX>-36</se:DisplacementX>', body)
+        self.assertIn('<se:DisplacementY>-18</se:DisplacementY>', body)
+
 
 if __name__ == '__main__':
     unittest.main()

tests/src/python/test_qgssymbollayer_createsld.py

@@ -98,6 +98,12 @@ def testSimpleMarkerUnitDefault(self):
         self.assertStrokeWidth(root, 2, 11)
         self.assertStaticDisplacement(root, 18, 36)
 
+        # Check negative offset
+        symbol.setOffset(QPointF(-5, -10))
+        dom, root = self.symbolToSld(symbol)
+        # print("Simple marker unit mm: " + root.ownerDocument().toString())
+        self.assertStaticDisplacement(root, -18, -36)
+
     def testSimpleMarkerUnitPixels(self):
         symbol = QgsSimpleMarkerSymbolLayer(
             QgsSimpleMarkerSymbolLayerBase.Shape.Star, color=QColor(255, 0, 0), strokeColor=QColor(0, 255, 0), size=10)