fix issues with align dash pattern (fix qgis#45432)

src/core/symbology/qgslinesymbollayer.cpp

@@ -777,15 +777,17 @@ void QgsSimpleLineSymbolLayer::drawPathWithDashPatternTweaks( QPainter *painter,
   if ( pen.dashPattern().empty() || points.size() < 2 )
     return;
 
+  if ( pen.widthF() <= 1.0 )
+  {
+    pen.setWidthF( 1.0001 );
+  }
+
   QVector< qreal > sourcePattern = pen.dashPattern();
-  const double dashWidthDiv = std::max( 1.0001, pen.widthF() );
+  const double dashWidthDiv = pen.widthF();
   // back to painter units
   for ( int i = 0; i < sourcePattern.size(); ++ i )
     sourcePattern[i] *= pen.widthF();
 
-  if ( pen.widthF() <= 1.0 )
-    pen.setWidthF( 1.0001 );
-
   QVector< qreal > buffer;
   QPolygonF bufferedPoints;
   QPolygonF previousSegmentBuffer;
@@ -960,6 +962,10 @@ void QgsSimpleLineSymbolLayer::drawPathWithDashPatternTweaks( QPainter *painter,
           patternIndex++;
           currentRemainingDashLength = 0.0;
           currentRemainingGapLength = sourcePattern.at( patternIndex );
+          if ( currentRemainingGapLength == 0.0 )
+          {
+            patternIndex++;
+          }
         }
         else
         {
@@ -992,8 +998,10 @@ void QgsSimpleLineSymbolLayer::drawPathWithDashPatternTweaks( QPainter *painter,
         }
       }
 
-      if ( patternIndex >= sourcePattern.size() )
+      if ( patternIndex + 1 >= sourcePattern.size() )
+      {
         patternIndex = 0;
+      }
 
       const double nextPatternDashLength = sourcePattern.at( patternIndex );
       const double nextPatternGapLength = sourcePattern.at( patternIndex + 1 );

tests/src/python/test_qgssimplelinesymbollayer.py

@@ -188,7 +188,6 @@ def testTrimDistanceRenderDataDefined(self):
         )
 
     def testDashPatternOffset(self):
-
         s = QgsLineSymbol.createSimple({'outline_color': '#ff0000', 'outline_width': '0.6'})
 
         s.symbolLayer(0).setDashPatternOffset(1.2)
@@ -333,6 +332,17 @@ def testDashCornerTweakDashRender(self):
             )
         )
 
+    def testAlignDashRenderSmallWidth(self):
+        # rendering test
+        s = QgsLineSymbol.createSimple({'outline_color': '#ff0000', 'outline_width': '0.1'})
+
+        s.symbolLayer(0).setPenStyle(Qt.DashDotDotLine)
+        s.symbolLayer(0).setAlignDashPattern(True)
+
+        g = QgsGeometry.fromWkt('LineString(0 0, 9.2 0, 9.2 10, 1.3 10)')
+        rendered_image = self.renderGeometry(s, g)
+        assert self.imageCheck('simpleline_aligndashpattern_small_width', 'simpleline_aligndashpattern_small_width', rendered_image)
+
     def testRingNumberVariable(self):
         # test test geometry_ring_num variable
         s3 = QgsFillSymbol()