Fix distorted line pattern fill when line offset is large compared

with pattern distance

src/core/symbology/qgsfillsymbollayer.cpp

@@ -1163,7 +1163,7 @@ void QgsShapeburstFillSymbolLayer::renderPolygon( const QPolygonF &points, QList
   if ( !useWholeShape && !qgsDoubleNear( maxDistance, 0.0 ) )
   {
     //convert max distance to pixels
-    outputPixelMaxDist = context.renderContext().convertToPainterUnits( maxDistance, mDistanceUnit, mDistanceMapUnitScale );
+    outputPixelMaxDist = static_cast< int >( std::round( context.renderContext().convertToPainterUnits( maxDistance, mDistanceUnit, mDistanceMapUnitScale ) ) );
   }
 
   //if we are using the two color mode, create a gradient ramp
@@ -2506,6 +2506,15 @@ void QgsLinePatternFillSymbolLayer::applyPattern( const QgsSymbolRenderContext &
   double outputPixelDist = ctx.convertToPainterUnits( distance, mDistanceUnit, mDistanceMapUnitScale );
   double outputPixelOffset = ctx.convertToPainterUnits( mOffset, mOffsetUnit, mOffsetMapUnitScale );
 
+  // NOTE: this may need to be modified if we ever change from a forced rasterized/brush approach,
+  // because potentially we may want to allow vector based line pattern fills where the first line
+  // is offset by a large distance
+
+  // fix truncated pattern with larger offsets
+  outputPixelOffset = std::fmod( outputPixelOffset, outputPixelDist );
+  if ( outputPixelOffset > outputPixelDist / 2.0 )
+    outputPixelOffset -= outputPixelDist;
+
   // To get all patterns into image, we have to consider symbols size (estimateMaxBleed()).
   // For marker lines we have to get markers interval.
   double outputPixelBleed = 0;
@@ -2590,7 +2599,7 @@ void QgsLinePatternFillSymbolLayer::applyPattern( const QgsSymbolRenderContext &
 
   // Add buffer based on bleed but keep precisely the height/width ratio (angle)
   // thus we add integer multiplications of width and height covering the bleed
-  int bufferMulti = std::max( std::ceil( outputPixelBleed / width ), std::ceil( outputPixelBleed / width ) );
+  int bufferMulti = static_cast< int >( std::max( std::ceil( outputPixelBleed / width ), std::ceil( outputPixelBleed / width ) ) );
 
   // Always buffer at least once so that center of line marker in upper right corner
   // does not fall outside due to representation error

tests/src/core/testqgslinefillsymbol.cpp

@@ -55,6 +55,7 @@ class TestQgsLineFillSymbol : public QObject
 
     void lineFillSymbol();
     void lineFillSymbolOffset();
+    void lineFillLargeOffset();
 
     void dataDefinedSubSymbol();
 
@@ -153,6 +154,17 @@ void TestQgsLineFillSymbol::lineFillSymbolOffset()
   mLineFill->setOffset( 0 );
 }
 
+void TestQgsLineFillSymbol::lineFillLargeOffset()
+{
+  // test line fill with large offset compared to line distance
+  mLineFill->setOffset( 8 );
+  QVERIFY( imageCheck( QStringLiteral( "symbol_linefill_large_posoffset" ) ) );
+
+  mLineFill->setOffset( -8 );
+  QVERIFY( imageCheck( QStringLiteral( "symbol_linefill_large_negoffset" ) ) );
+  mLineFill->setOffset( 0 );
+}
+
 void TestQgsLineFillSymbol::dataDefinedSubSymbol()
 {
   mReport += QLatin1String( "<h2>Line fill symbol data defined sub symbol test</h2>\n" );