Fix rendering of linestrings with nan z values

src/core/symbology/qgssymbol.cpp

@@ -26,9 +26,6 @@
 #include "qgssymbol.h"
 #include "qgssymbollayer.h"
 
-#include "qgslinesymbollayer.h"
-#include "qgsmarkersymbollayer.h"
-#include "qgsfillsymbollayer.h"
 #include "qgsgeometrygeneratorsymbollayer.h"
 #include "qgsmaptopixelgeometrysimplifier.h"
 #include "qgslogger.h"
@@ -37,7 +34,6 @@
 #include "qgsprojectstylesettings.h"
 #include "qgsstyle.h"
 #include "qgspainteffect.h"
-#include "qgseffectstack.h"
 #include "qgsvectorlayer.h"
 #include "qgsfeature.h"
 #include "qgsgeometry.h"
@@ -142,10 +138,13 @@ QPolygonF QgsSymbol::_getLineString3d( QgsRenderContext &context, const QgsCurve
   }
 
   // transform the points to screen coordinates
+  const QVector< double > preTransformPointsZ = pointsZ;
+  bool wasTransformed = false;
   if ( ct.isValid() )
   {
     //create x, y arrays
     const int nVertices = pointsX.size();
+    wasTransformed = true;
 
     try
     {
@@ -164,13 +163,25 @@ QPolygonF QgsSymbol::_getLineString3d( QgsRenderContext &context, const QgsCurve
     const double *xIn = pointsX.data();
     const double *yIn = pointsY.data();
     const double *zIn = pointsZ.data();
+
+    const double *preTransformZIn = wasTransformed ? preTransformPointsZ.constData() : nullptr;
+
     double *xOut = pointsX.data();
     double *yOut = pointsY.data();
     double *zOut = pointsZ.data();
     int outSize = 0;
     for ( int i = 0; i < size; ++i )
     {
-      if ( std::isfinite( *xIn ) && std::isfinite( *yIn ) && std::isfinite( *zIn ) )
+      bool pointOk = std::isfinite( *xIn ) && std::isfinite( *yIn );
+
+      // skip z points which have been made non-finite during transformations only. Ie if:
+      // - we did no transformation, then always render even if non-finite z
+      // - we did transformation and z is finite then render
+      // - we did transformation and z is non-finite BUT input z was also non finite then render
+      // - we did transformation and z is non-finite AND input z WAS finite then skip
+      pointOk &= !wasTransformed || std::isfinite( *zIn ) || !std::isfinite( *preTransformZIn );
+
+      if ( pointOk )
       {
         *xOut++ = *xIn++;
         *yOut++ = *yIn++;
@@ -183,6 +194,9 @@ QPolygonF QgsSymbol::_getLineString3d( QgsRenderContext &context, const QgsCurve
         yIn++;
         zIn++;
       }
+
+      if ( preTransformZIn )
+        preTransformZIn++;
     }
     pointsX.resize( outSize );
     pointsY.resize( outSize );

tests/src/python/test_qgssymbol.py

@@ -60,7 +60,8 @@
                        Qgis,
                        QgsSymbolLayer,
                        QgsProperty,
-                       QgsRasterFillSymbolLayer
+                       QgsRasterFillSymbolLayer,
+                       QgsPoint
                        )
 
 from qgis.testing import unittest, start_app
@@ -719,6 +720,43 @@ def renderCollection(self, geom, symbol):
 
         return image
 
+    def test_render_line_nan_z(self):
+        geom = QgsGeometry.fromPolyline([
+            QgsPoint(10, 10, 0),
+            QgsPoint(20, 20, 0),
+            QgsPoint(30, 10, float("nan")),
+        ])
+
+        f = QgsFeature()
+        f.setGeometry(geom)
+
+        image = QImage(200, 200, QImage.Format_RGB32)
+
+        painter = QPainter()
+        ms = QgsMapSettings()
+        extent = geom.get().boundingBox()
+        # buffer extent by 10%
+        extent = extent.buffered((extent.height() + extent.width()) / 20.0)
+
+        ms.setExtent(extent)
+        ms.setOutputSize(image.size())
+        context = QgsRenderContext.fromMapSettings(ms)
+        context.setPainter(painter)
+        context.setScaleFactor(96 / 25.4)  # 96 DPI
+
+        symbol = QgsLineSymbol.createSimple({'color': '#ffffff', 'line_width': '3'})
+
+        painter.begin(image)
+        try:
+            image.fill(QColor(0, 0, 0))
+            symbol.startRender(context)
+            symbol.renderFeature(f, context)
+            symbol.stopRender(context)
+        finally:
+            painter.end()
+
+        assert self.imageCheck('Linestring with nan z', 'linestring_nan_z', image)
+
     def testGeometryCollectionRender(self):
         tests = [{'name': 'Marker',
                   'wkt': 'GeometryCollection (Point(1 2))',