Use 'fast clip' line clipping algorithm for long lines. Huge improvement for wms benchmark performance (long contour lines)

git-svn-id: http://svn.osgeo.org/qgis/trunk@15090 c8812cc2-4d05-0410-92ff-de0c093fc19c

Author: mhugent

src/core/qgsclipper.cpp

@@ -35,3 +35,171 @@ const double QgsClipper::MAX_Y =  16000;
 const double QgsClipper::MIN_Y = -16000;
 
 const double QgsClipper::SMALL_NUM = 1e-12;
+
+unsigned char* QgsClipper::clippedLineWKB( unsigned char* wkb, const QgsRectangle& clipExtent, QPolygonF& line )
+{
+  wkb++; // jump over endian info
+  unsigned int wkbType = *(( int* ) wkb );
+  wkb += sizeof( unsigned int );
+  unsigned int nPoints = *(( int* ) wkb );
+  wkb += sizeof( unsigned int );
+
+  bool hasZValue = ( wkbType == QGis::WKBLineString25D );
+
+  double p0x, p0y, p1x, p1y; //original coordinates
+  double p1x_c, p1y_c; //clipped end coordinates
+  double lastClipX, lastClipY; //last successfully clipped coords
+
+  line.reserve( nPoints + 1 );
+  line.clear();
+
+  for ( unsigned int i = 0; i < nPoints; ++i )
+  {
+    if ( i == 0 )
+    {
+      memcpy( &p1x, wkb, sizeof( double ) );
+      wkb += sizeof( double );
+      memcpy( &p1y, wkb, sizeof( double ) );
+      wkb += sizeof( double );
+      if ( hasZValue ) // ignore Z value
+      {
+        wkb += sizeof( double );
+      }
+      continue;
+    }
+    else
+    {
+      p0x = p1x;
+      p0y = p1y;
+
+      memcpy( &p1x, wkb, sizeof( double ) );
+      wkb += sizeof( double );
+      memcpy( &p1y, wkb, sizeof( double ) );
+      wkb += sizeof( double );
+      if ( hasZValue ) // ignore Z value
+      {
+        wkb += sizeof( double );
+      }
+
+      p1x_c = p1x; p1y_c = p1y;
+      if ( clipLineSegment( clipExtent.xMinimum(), clipExtent.xMaximum(), clipExtent.yMinimum(), clipExtent.yMaximum(),
+                            p0x, p0y, p1x_c,  p1y_c ) )
+      {
+        bool newLine = line.size() > 0 && ( p1x_c != lastClipX || p1y_c != lastClipY );
+        if ( newLine )
+        {
+          //add edge points to connect old and new line
+          connectSeparatedLines( lastClipX, lastClipY, p0x, p0y, clipExtent, line );
+        }
+        if ( line.size() < 1 || newLine )
+        {
+          //add first point
+          line << QPointF( p0x, p0y );
+        }
+
+        //add second point
+        lastClipX = p1x_c; lastClipY = p1y_c;
+        line << QPointF( p1x_c,  p1y_c );
+      }
+    }
+  }
+  return wkb;
+}
+
+void QgsClipper::connectSeparatedLines( double x0, double y0, double x1, double y1,
+                                        const QgsRectangle& clipRect, QPolygonF& pts )
+{
+  //test the different edge combinations...
+  if ( doubleNear( x0, clipRect.xMinimum() ) )
+  {
+    if ( doubleNear( x1, clipRect.xMinimum() ) )
+    {
+      return;
+    }
+    else if ( doubleNear( y1, clipRect.yMaximum() ) )
+    {
+      pts << QPointF( clipRect.xMinimum(), clipRect.yMaximum() );
+      return;
+    }
+    else if ( doubleNear( x1, clipRect.xMaximum() ) )
+    {
+      pts << QPointF( clipRect.xMinimum(), clipRect.yMaximum() );
+      pts << QPointF( clipRect.xMaximum(), clipRect.yMaximum() );
+      return;
+    }
+    else if ( doubleNear( y1, clipRect.yMinimum() ) )
+    {
+      pts << QPointF( clipRect.xMinimum(), clipRect.yMinimum() );
+      return;
+    }
+  }
+  else if ( doubleNear( y0, clipRect.yMaximum() ) )
+  {
+    if ( doubleNear( y1, clipRect.yMaximum() ) )
+    {
+      return;
+    }
+    else if ( doubleNear( x1, clipRect.xMaximum() ) )
+    {
+      pts << QPointF( clipRect.xMaximum(), clipRect.yMaximum() );
+      return;
+    }
+    else if ( doubleNear( y1, clipRect.yMinimum() ) )
+    {
+      pts << QPointF( clipRect.xMaximum(), clipRect.yMaximum() );
+      pts << QPointF( clipRect.xMaximum(), clipRect.yMinimum() );
+      return;
+    }
+    else if ( doubleNear( x1, clipRect.xMinimum() ) )
+    {
+      pts << QPointF( clipRect.xMinimum(), clipRect.yMaximum() );
+      return;
+    }
+  }
+  else if ( doubleNear( x0, clipRect.xMaximum() ) )
+  {
+    if ( doubleNear( x1, clipRect.xMaximum() ) )
+    {
+      return;
+    }
+    else if ( doubleNear( y1, clipRect.yMinimum() ) )
+    {
+      pts << QPointF( clipRect.xMaximum(), clipRect.yMinimum() );
+      return;
+    }
+    else if ( doubleNear( x1, clipRect.xMinimum() ) )
+    {
+      pts << QPointF( clipRect.xMaximum(), clipRect.yMinimum() );
+      pts << QPointF( clipRect.xMinimum(), clipRect.yMinimum() );
+      return;
+    }
+    else if ( doubleNear( y1, clipRect.yMaximum() ) )
+    {
+      pts << QPointF( clipRect.xMaximum(), clipRect.yMaximum() );
+      return;
+    }
+  }
+  else if ( doubleNear( y0, clipRect.yMinimum() ) )
+  {
+    if ( doubleNear( y1, clipRect.yMinimum() ) )
+    {
+      return;
+    }
+    else if ( doubleNear( x1, clipRect.xMinimum() ) )
+    {
+      pts << QPointF( clipRect.xMinimum(), clipRect.yMinimum() );
+      return;
+    }
+    else if ( doubleNear( y1, clipRect.yMaximum() ) )
+    {
+      pts << QPointF( clipRect.xMinimum(), clipRect.yMinimum() );
+      pts << QPointF( clipRect.xMinimum(), clipRect.yMaximum() );
+      return;
+    }
+    else if ( doubleNear( x1, clipRect.xMaximum() ) )
+    {
+      pts << QPointF( clipRect.xMaximum(), clipRect.yMinimum() );
+      return;
+    }
+  }
+}