Properly reserve place for arrays in line and polygon clipping routines

A QVector::clear() method completely reinitializes the object. Calling a QVector::reserve() before clear() is useless and causes big overhead at array append operations. Give ~6% perfomance gain. Signed-off-by: Yauhen Kharuzhy <jekhor@gmail.com>
qgis · Dec 9, 2013 · 221263d · 221263d
1 parent 381efba
commit 221263d
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Showing 2 changed files with 4 additions and 4 deletions.
diff --git a/src/core/qgsclipper.cpp b/src/core/qgsclipper.cpp
@@ -49,8 +49,8 @@ const unsigned char* QgsClipper::clippedLineWKB( const unsigned char* wkb, const
   double p1x_c, p1y_c; //clipped end coordinates
   double lastClipX = 0.0, lastClipY = 0.0; //last successfully clipped coords
 
-  line.reserve( nPoints + 1 );
   line.clear();
+  line.reserve( nPoints + 1 );
 
   for ( unsigned int i = 0; i < nPoints; ++i )
   {

diff --git a/src/core/qgsclipper.h b/src/core/qgsclipper.h
@@ -179,11 +179,11 @@ inline void QgsClipper::trimPolygon( QPolygonF& pts, const QgsRectangle& clipRec
   tmpPts.reserve( pts.size() );
 
   trimPolygonToBoundary( pts, tmpPts, clipRect, XMax, clipRect.xMaximum() );
-  pts.clear();
+  pts.resize( 0 );
   trimPolygonToBoundary( tmpPts, pts, clipRect, YMax, clipRect.yMaximum() );
-  tmpPts.clear();
+  tmpPts.resize( 0 );
   trimPolygonToBoundary( pts, tmpPts, clipRect, XMin, clipRect.xMinimum() );
-  pts.clear();
+  pts.resize( 0 );
   trimPolygonToBoundary( tmpPts, pts, clipRect, YMin, clipRect.yMinimum() );
 }