Add QgsSymbol::canCauseArtifactsBetweenAdjacentTiles()

Returns True if ANY of the symbol layers contained in the symbol can cause tile rendering artifacts
qgis · Feb 12, 2021 · f75c53b · f75c53b
1 parent bdf5e4f
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Showing 4 changed files with 48 additions and 2 deletions.
diff --git a/python/core/auto_generated/symbology/qgssymbol.sip.in b/python/core/auto_generated/symbology/qgssymbol.sip.in
@@ -556,6 +556,17 @@ Sets the symbol's property collection, used for data defined overrides.
 Returns whether the symbol utilizes any data defined properties.
 
 .. versionadded:: 2.12
+%End
+
+    bool canCauseArtifactsBetweenAdjacentTiles() const;
+%Docstring
+Returns ``True`` if the symbol rendering can cause visible artifacts across a single feature
+when the feature is rendered as a series of adjacent map tiles each containing a portion of the feature's geometry.
+
+Internally this calls :py:func:`QgsSymbolLayer.canCauseArtifactsBetweenAdjacentTiles()` for all symbol layers in the symbol
+and returns ``True`` if any of the layers returned ``True``.
+
+.. versionadded:: 3.18
 %End
 
  void setLayer( const QgsVectorLayer *layer ) /Deprecated/;

diff --git a/src/core/symbology/qgssymbol.cpp b/src/core/symbology/qgssymbol.cpp
@@ -813,15 +813,24 @@ bool QgsSymbol::hasDataDefinedProperties() const
   if ( mDataDefinedProperties.hasActiveProperties() )
     return true;
 
-  const auto constMLayers = mLayers;
-  for ( QgsSymbolLayer *layer : constMLayers )
+  for ( QgsSymbolLayer *layer : mLayers )
   {
     if ( layer->hasDataDefinedProperties() )
       return true;
   }
   return false;
 }
 
+bool QgsSymbol::canCauseArtifactsBetweenAdjacentTiles() const
+{
+  for ( QgsSymbolLayer *layer : mLayers )
+  {
+    if ( layer->canCauseArtifactsBetweenAdjacentTiles() )
+      return true;
+  }
+  return false;
+}
+
 void QgsSymbol::setLayer( const QgsVectorLayer *layer )
 {
   Q_NOWARN_DEPRECATED_PUSH

diff --git a/src/core/symbology/qgssymbol.h b/src/core/symbology/qgssymbol.h
@@ -588,6 +588,17 @@ class CORE_EXPORT QgsSymbol
      */
     bool hasDataDefinedProperties() const;
 
+    /**
+     * Returns TRUE if the symbol rendering can cause visible artifacts across a single feature
+     * when the feature is rendered as a series of adjacent map tiles each containing a portion of the feature's geometry.
+     *
+     * Internally this calls QgsSymbolLayer::canCauseArtifactsBetweenAdjacentTiles() for all symbol layers in the symbol
+     * and returns TRUE if any of the layers returned TRUE.
+     *
+     * \since QGIS 3.18
+     */
+    bool canCauseArtifactsBetweenAdjacentTiles() const;
+
     /**
      * \note the layer will be NULLPTR after stopRender
      * \deprecated Will be removed in QGIS 4.0

diff --git a/tests/src/python/test_qgssymbol.py b/tests/src/python/test_qgssymbol.py
@@ -54,6 +54,7 @@
                        QgsReadWriteContext,
                        QgsSymbolLayerUtils,
                        QgsMarkerLineSymbolLayer,
+                       QgsArrowSymbolLayer,
                        QgsSymbol
                        )
 
@@ -148,6 +149,20 @@ def testPythonAdditions(self):
         layers = [l.color().name() for l in markerSymbol]
         self.assertEqual(layers, ['#ff0000'])
 
+    def testCanCauseArtifactsBetweenAdjacentTiles(self):
+        """
+        Test canCauseArtifactsBetweenAdjacentTiles()
+        """
+
+        # start with a symbol which won't cause artifacts -- a simple line symbol
+        symbol = QgsLineSymbol.createSimple({})
+        self.assertFalse(symbol.canCauseArtifactsBetweenAdjacentTiles())
+        # add a second layer which CAN cause artifacts
+        symbol.appendSymbolLayer(QgsArrowSymbolLayer())
+        self.assertTrue(symbol.canCauseArtifactsBetweenAdjacentTiles())
+        symbol.deleteSymbolLayer(0)
+        self.assertTrue(symbol.canCauseArtifactsBetweenAdjacentTiles())
+
     def testGeometryRendering(self):
         '''Tests rendering a bunch of different geometries, including bad/odd geometries.'''