[composer] Use intersection rather than clip for transformed grids

Previous behaviour was to clip transformed grid lines to the visible
map extent. This caused problems if a map item had no border (a
solid line would be shown along the map extent), and also meant
that reprojected lines which crossed out of the map extent and back
in again did not have annotations or grid frame markings shown.

Also implement an improved logic for detecting the map frame side
for annotations.

Author: nyalldawson

src/core/composer/qgscomposermapgrid.cpp

@@ -1615,11 +1615,15 @@ int QgsComposerMapGrid::xGridLinesCRSTransform( const QgsRectangle& bbox, const
     }
     crossed180 = false;
 
-    gridLine = trimLineToMap( gridLine, QgsRectangle( mComposerMap->rect() ) );
-    if ( gridLine.size() > 0 )
+    QList<QPolygonF> lineSegments = trimLinesToMap( gridLine, QgsRectangle( mComposerMap->rect() ) );
+    QList<QPolygonF>::const_iterator lineIt = lineSegments.constBegin();
+    for ( ; lineIt != lineSegments.constEnd(); lineIt ++ )
     {
-      lines.append( qMakePair( currentLevel, gridLine ) );
-      gridLineCount++;
+      if (( *lineIt ).size() > 0 )
+      {
+        lines.append( qMakePair( currentLevel, *lineIt ) );
+        gridLineCount++;
+      }
     }
     currentLevel -= mGridIntervalY;
   }
@@ -1677,11 +1681,15 @@ int QgsComposerMapGrid::yGridLinesCRSTransform( const QgsRectangle& bbox, const
       currentY += step;
     }
     //clip grid line to map polygon
-    gridLine = trimLineToMap( gridLine, QgsRectangle( mComposerMap->rect() ) );
-    if ( gridLine.size() > 0 )
+    QList<QPolygonF> lineSegments = trimLinesToMap( gridLine, QgsRectangle( mComposerMap->rect() ) );
+    QList<QPolygonF>::const_iterator lineIt = lineSegments.constBegin();
+    for ( ; lineIt != lineSegments.constEnd(); lineIt ++ )
     {
-      lines.append( qMakePair( currentLevel, gridLine ) );
-      gridLineCount++;
+      if (( *lineIt ).size() > 0 )
+      {
+        lines.append( qMakePair( currentLevel, *lineIt ) );
+        gridLineCount++;
+      }
     }
     currentLevel += mGridIntervalX;
     if ( crosses180 && currentLevel > 180.0 )
@@ -1775,26 +1783,31 @@ bool QgsComposerMapGrid::shouldShowDivisionForDisplayMode( const QgsComposerMapG
          || ( mode == QgsComposerMapGrid::LongitudeOnly && coordinate == QgsComposerMapGrid::Longitude );
 }
 
+bool sortByDistance( const QPair<double, QgsComposerMapGrid::BorderSide>& a, const QPair<double, QgsComposerMapGrid::BorderSide>& b )
+{
+  return a.first < b.first;
+}
+
 QgsComposerMapGrid::BorderSide QgsComposerMapGrid::borderForLineCoord( const QPointF& p, const AnnotationCoordinate coordinateType ) const
 {
   if ( !mComposerMap )
   {
     return QgsComposerMapGrid::Left;
   }
 
-  double framePenWidth = mComposerMap->hasFrame() ? mComposerMap->pen().widthF() : 0.000000001;
+  double tolerance = qMax( mComposerMap->hasFrame() ? mComposerMap->pen().widthF() : 0.0, 1.0 );
 
   //check for corner coordinates
-  if (( p.y() <= framePenWidth && p.x() <= framePenWidth )  // top left
-      || ( p.y() <= framePenWidth && p.x() >= ( mComposerMap->rect().width() - framePenWidth ) ) //top right
-      || ( p.y() >= ( mComposerMap->rect().height() - framePenWidth ) && p.x() <= framePenWidth ) //bottom left
-      || ( p.y() >= ( mComposerMap->rect().height() - framePenWidth ) && p.x() >= ( mComposerMap->rect().width() - framePenWidth ) ) //bottom right
+  if (( p.y() <= tolerance && p.x() <= tolerance )  // top left
+      || ( p.y() <= tolerance && p.x() >= ( mComposerMap->rect().width() - tolerance ) ) //top right
+      || ( p.y() >= ( mComposerMap->rect().height() - tolerance ) && p.x() <= tolerance ) //bottom left
+      || ( p.y() >= ( mComposerMap->rect().height() - tolerance ) && p.x() >= ( mComposerMap->rect().width() - tolerance ) ) //bottom right
      )
   {
     //coordinate is in corner - fall back to preferred side for coordinate type
     if ( coordinateType == QgsComposerMapGrid::Latitude )
     {
-      if ( p.x() <= framePenWidth )
+      if ( p.x() <= tolerance )
       {
         return QgsComposerMapGrid::Left;
       }
@@ -1805,7 +1818,7 @@ QgsComposerMapGrid::BorderSide QgsComposerMapGrid::borderForLineCoord( const QPo
     }
     else
     {
-      if ( p.y() <= framePenWidth )
+      if ( p.y() <= tolerance )
       {
         return QgsComposerMapGrid::Top;
       }
@@ -1816,23 +1829,15 @@ QgsComposerMapGrid::BorderSide QgsComposerMapGrid::borderForLineCoord( const QPo
     }
   }
 
-  //otherwise, guess side based on point
-  if ( p.y() <= framePenWidth )
-  {
-    return QgsComposerMapGrid::Top;
-  }
-  else if ( p.x() <= framePenWidth )
-  {
-    return QgsComposerMapGrid::Left;
-  }
-  else if ( p.x() >= ( mComposerMap->rect().width() - framePenWidth ) )
-  {
-    return QgsComposerMapGrid::Right;
-  }
-  else
-  {
-    return QgsComposerMapGrid::Bottom;
-  }
+  //otherwise, guess side based on closest map side to point
+  QList< QPair<double, QgsComposerMapGrid::BorderSide > > distanceToSide;
+  distanceToSide << qMakePair( p.x(), QgsComposerMapGrid::Left );
+  distanceToSide << qMakePair( mComposerMap->rect().width() - p.x(), QgsComposerMapGrid::Right );
+  distanceToSide << qMakePair( p.y(), QgsComposerMapGrid::Top );
+  distanceToSide << qMakePair( mComposerMap->rect().height() - p.y(), QgsComposerMapGrid::Bottom );
+
+  qSort( distanceToSide.begin(), distanceToSide.end(), sortByDistance );
+  return distanceToSide.at( 0 ).second;
 }
 
 void QgsComposerMapGrid::setLineSymbol( QgsLineSymbolV2* symbol )
@@ -2268,21 +2273,25 @@ int QgsComposerMapGrid::crsGridParams( QgsRectangle& crsRect, QgsCoordinateTrans
   return 0;
 }
 
-QPolygonF QgsComposerMapGrid::trimLineToMap( const QPolygonF& line, const QgsRectangle& rect )
+QList<QPolygonF> QgsComposerMapGrid::trimLinesToMap( const QPolygonF& line, const QgsRectangle& rect )
 {
-  QgsPolyline polyLine;
-  QPolygonF::const_iterator lineIt = line.constBegin();
-  for ( ; lineIt != line.constEnd(); ++lineIt )
+  QgsGeometry* lineGeom = QgsGeometry::fromQPolygonF( line );
+  QgsGeometry* rectGeom = QgsGeometry::fromRect( rect );
+
+  QgsGeometry* intersected = lineGeom->intersection( rectGeom );
+  QList<QgsGeometry*> intersectedParts = intersected->asGeometryCollection();
+
+  QList<QPolygonF> trimmedLines;
+  QList<QgsGeometry*>::const_iterator geomIt = intersectedParts.constBegin();
+  for ( ; geomIt != intersectedParts.constEnd(); geomIt++ )
   {
-    polyLine.append( QgsPoint( lineIt->x(), lineIt->y() ) );
+    trimmedLines << ( *geomIt )->asQPolygonF();
   }
 
-  QgsGeometry* geom = QgsGeometry::fromPolyline( polyLine );
-
-  QPolygonF clippedLine;
-  QgsClipper::clippedLineWKB( geom->asWkb(), rect, clippedLine );
-  delete geom;
-  return clippedLine;
+  qDeleteAll( intersectedParts );
+  intersectedParts.clear();
+  delete intersected;
+  delete lineGeom;
+  delete rectGeom;
+  return trimmedLines;
 }
-
-

src/core/composer/qgscomposermapgrid.h

@@ -931,7 +931,7 @@ class CORE_EXPORT QgsComposerMapGrid : public QgsComposerMapItem
     /**Get parameters for drawing grid in CRS different to map CRS*/
     int crsGridParams( QgsRectangle& crsRect, QgsCoordinateTransform& inverseTransform ) const;
 
-    static QPolygonF trimLineToMap( const QPolygonF& line, const QgsRectangle& rect );
+    static QList<QPolygonF> trimLinesToMap( const QPolygonF &line, const QgsRectangle &rect );
 
     QPolygonF scalePolygon( const QPolygonF &polygon, const double scale ) const;
 

tests/src/core/testqgscomposermapgrid.cpp

@@ -35,6 +35,7 @@ class TestQgsComposerMapGrid: public QObject
     void init();// will be called before each testfunction is executed.
     void cleanup();// will be called after every testfunction.
     void grid(); //test if grid and grid annotation works
+    void reprojected(); //test if reprojected grid works
     void crossGrid(); //test if grid "cross" mode works
     void markerGrid(); //test if grid "marker" mode works
     void frameOnly(); //test if grid "frame/annotation" mode works
@@ -128,6 +129,31 @@ void TestQgsComposerMapGrid::grid()
   QVERIFY( testResult );
 }
 
+void TestQgsComposerMapGrid::reprojected()
+{
+  mComposerMap->setNewExtent( QgsRectangle( -243577.565, 2939084.773, 1215622.435, 3668684.773 ) );
+  QgsCoordinateReferenceSystem geographic = QgsCoordinateReferenceSystem( 4326 );
+  mComposerMap->grid()->setCrs( geographic );
+  mComposerMap->grid()->setEnabled( true );
+  mComposerMap->grid()->setIntervalX( 1 );
+  mComposerMap->grid()->setIntervalY( 1 );
+  mComposerMap->grid()->setAnnotationEnabled( false );
+  mComposerMap->grid()->setGridLineColor( QColor( 0, 0, 0 ) );
+  mComposerMap->grid()->setGridLineWidth( 0.5 );
+  mComposerMap->grid()->setBlendMode( QPainter::CompositionMode_SourceOver );
+  mComposerMap->grid()->setFrameStyle( QgsComposerMapGrid::ExteriorTicks );
+  mComposerMap->grid()->setFrameWidth( 10 );
+  mComposerMap->setFrameEnabled( false );
+  QgsCompositionChecker checker( "composermap_gridreprojected", mComposition );
+
+  bool testResult = checker.testComposition( mReport, 0, 0 );
+  mComposerMap->grid()->setEnabled( false );
+  mComposerMap->grid()->setCrs( mMapSettings.destinationCrs() );
+  mComposerMap->grid()->setFrameStyle( QgsComposerMapGrid::NoFrame );
+  mComposerMap->setFrameEnabled( true );
+  QVERIFY( testResult );
+}
+
 void TestQgsComposerMapGrid::crossGrid()
 {
   mComposerMap->setNewExtent( QgsRectangle( 781662.375, 3339523.125, 793062.375, 3345223.125 ) );
@@ -177,6 +203,7 @@ void TestQgsComposerMapGrid::frameOnly()
   mComposerMap->grid()->setAnnotationEnabled( false );
   //set a frame for testing
   mComposerMap->grid()->setFrameStyle( QgsComposerMapGrid::Zebra );
+  mComposerMap->grid()->setFrameWidth( 2.0 );
   mComposerMap->grid()->setFramePenSize( 0.5 );
   mComposerMap->grid()->setBlendMode( QPainter::CompositionMode_SourceOver );
   QgsCompositionChecker checker( "composermap_gridframeonly", mComposition );