[composer] Fix incorrect calculation of scale for tick scale bars

QPainter::drawLine(x1,y1,x2,y2) takes int values, so coordinates
were being rounded to the nearest mm. Consequently scale was way
off. Also fixes horizontal line for tick styles being drawn
incorrectly with multiple overlapping segments. (fix #10685)

src/core/composer/qgscomposerscalebar.cpp

@@ -434,10 +434,11 @@ void QgsComposerScaleBar::segmentPositions( QList<QPair<double, double> >& posWi
   double mCurrentXCoord = mPen.widthF() + mBoxContentSpace;
 
   //left segments
+  double leftSegmentSize = mSegmentMillimeters / mNumSegmentsLeft;
   for ( int i = 0; i < mNumSegmentsLeft; ++i )
   {
-    posWidthList.push_back( qMakePair( mCurrentXCoord, mSegmentMillimeters / mNumSegmentsLeft ) );
-    mCurrentXCoord += mSegmentMillimeters / mNumSegmentsLeft;
+    posWidthList.push_back( qMakePair( mCurrentXCoord, leftSegmentSize ) );
+    mCurrentXCoord += leftSegmentSize;
   }
 
   //right segments

src/core/composer/qgsdoubleboxscalebarstyle.cpp

@@ -59,8 +59,6 @@ void QgsDoubleBoxScaleBarStyle::draw( QPainter* p, double xOffset ) const
 
   bool useColor = true; //alternate brush color/white
 
-
-
   QList<QPair<double, double> >::const_iterator segmentIt = segmentInfo.constBegin();
   for ( ; segmentIt != segmentInfo.constEnd(); ++segmentIt )
   {

src/core/composer/qgssingleboxscalebarstyle.cpp

@@ -48,7 +48,6 @@ void QgsSingleBoxScaleBarStyle::draw( QPainter* p, double xOffset ) const
   p->setRenderHint( QPainter::Antialiasing, true );
   p->setPen( mScaleBar->pen() );
 
-
   QList<QPair<double, double> > segmentInfo;
   mScaleBar->segmentPositions( segmentInfo );
 

src/core/composer/qgsticksscalebarstyle.cpp

@@ -69,26 +69,30 @@ void QgsTicksScaleBarStyle::draw( QPainter* p, double xOffset ) const
   QList<QPair<double, double> >::const_iterator segmentIt = segmentInfo.constBegin();
   for ( ; segmentIt != segmentInfo.constEnd(); ++segmentIt )
   {
-    p->drawLine( segmentIt->first + xOffset, barTopPosition, segmentIt->first + xOffset, barTopPosition + mScaleBar->height() );
+    p->drawLine( QLineF( segmentIt->first + xOffset, barTopPosition, segmentIt->first + xOffset, barTopPosition + mScaleBar->height() ) );
+  }
+
+  //draw last tick and horizontal line
+  if ( !segmentInfo.isEmpty() )
+  {
+    double lastTickPositionX = segmentInfo.last().first + mScaleBar->segmentMillimeters() + xOffset;
+    double verticalPos;
     switch ( mTickPosition )
     {
       case TicksDown:
-        p->drawLine( xOffset + segmentIt->first, barTopPosition, xOffset + segmentIt->first + mScaleBar->segmentMillimeters(), barTopPosition );
+        verticalPos = barTopPosition;
         break;
       case TicksMiddle:
-        p->drawLine( xOffset + segmentIt->first, middlePosition, xOffset + segmentIt->first + mScaleBar->segmentMillimeters(), middlePosition );
+        verticalPos = middlePosition;
         break;
       case TicksUp:
-        p->drawLine( xOffset + segmentIt->first, bottomPosition, xOffset + segmentIt->first + mScaleBar->segmentMillimeters(), bottomPosition );
+        verticalPos = bottomPosition;
         break;
     }
-  }
-
-  //draw last tick
-  if ( !segmentInfo.isEmpty() )
-  {
-    double lastTickPositionX = segmentInfo.last().first + mScaleBar->segmentMillimeters();
-    p->drawLine( lastTickPositionX + xOffset, barTopPosition, lastTickPositionX + xOffset, barTopPosition + mScaleBar->height() );
+    //horizontal line
+    p->drawLine( QLineF( xOffset + segmentInfo.at( 0 ).first, verticalPos, lastTickPositionX, verticalPos ) );
+    //last vertical line
+    p->drawLine( QLineF( lastTickPositionX, barTopPosition, lastTickPositionX, barTopPosition + mScaleBar->height() ) );
   }
 
   p->restore();