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QgsSymbol::renderFeature(): render larger parts of multipolygon first

When drawing an invalid multipolygon, that has a part inside another one,
there is a chance we draw first the smaller part and then the larger part,
making it invisible.
Change the drawing order to start with larger parts.

Fixes #15419
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rouault committed Oct 6, 2016
1 parent 7182b1b commit 893263952d190d9abc2f239fa513cb327df77bee
Showing with 37 additions and 17 deletions.
  1. +37 −17 src/core/symbology-ng/qgssymbol.cpp
@@ -47,6 +47,7 @@
#include <QSvgGenerator>

#include <cmath>
#include <map>

inline
QgsDataDefined* rotateWholeSymbol( double additionalRotation, const QgsDataDefined& dd )
@@ -842,30 +843,49 @@ void QgsSymbol::renderFeature( const QgsFeature& feature, QgsRenderContext& cont
const QgsGeometryCollection& geomCollection = dynamic_cast<const QgsGeometryCollection&>( *segmentizedGeometry.geometry() );
const unsigned int num = geomCollection.numGeometries();

// Sort components by approximate area (probably a bit faster than using
// area() )
std::map<double, QList<unsigned int> > mapAreaToPartNum;
for ( unsigned int i = 0; i < num; ++i )
{
mSymbolRenderContext->setGeometryPartNum( i + 1 );
mSymbolRenderContext->expressionContextScope()->setVariable( QgsExpressionContext::EXPR_GEOMETRY_PART_NUM, i + 1 );

context.setGeometry( geomCollection.geometryN( i ) );
const QgsPolygonV2& polygon = dynamic_cast<const QgsPolygonV2&>( *geomCollection.geometryN( i ) );
_getPolygon( pts, holes, context, polygon, !tileMapRendering && clipFeaturesToExtent() );
static_cast<QgsFillSymbol*>( this )->renderPolygon( pts, ( !holes.isEmpty() ? &holes : nullptr ), &feature, context, layer, selected );
const QgsRectangle r( polygon.boundingBox() );
mapAreaToPartNum[ r.width() * r.height()] << i;
}

if ( drawVertexMarker && !usingSegmentizedGeometry )
// Draw starting with larger parts down to smaller parts, so that in
// case of a part being incorrectly inside another part, it is drawn
// on top of it (#15419)
std::map<double, QList<unsigned int> >::const_reverse_iterator iter = mapAreaToPartNum.rbegin();
for ( ; iter != mapAreaToPartNum.rend(); ++iter )
{
const QList<unsigned int>& listPartIndex = iter->second;
for ( int idx = 0; idx < listPartIndex.size(); ++idx )
{
if ( i == 0 )
{
markers = pts;
}
else
{
markers << pts;
}
const unsigned i = listPartIndex[idx];
mSymbolRenderContext->setGeometryPartNum( i + 1 );
mSymbolRenderContext->expressionContextScope()->setVariable( QgsExpressionContext::EXPR_GEOMETRY_PART_NUM, i + 1 );

context.setGeometry( geomCollection.geometryN( i ) );
const QgsPolygonV2& polygon = dynamic_cast<const QgsPolygonV2&>( *geomCollection.geometryN( i ) );
_getPolygon( pts, holes, context, polygon, !tileMapRendering && clipFeaturesToExtent() );
static_cast<QgsFillSymbol*>( this )->renderPolygon( pts, ( !holes.isEmpty() ? &holes : nullptr ), &feature, context, layer, selected );

Q_FOREACH ( const QPolygonF& hole, holes )
if ( drawVertexMarker && !usingSegmentizedGeometry )
{
markers << hole;
if ( i == 0 )
{
markers = pts;
}
else
{
markers << pts;
}

Q_FOREACH ( const QPolygonF& hole, holes )
{
markers << hole;
}
}
}
}

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