SHAPE_LINE_CHAIN::Area() should always be positive

The algorithm relied on the assumption that the points were
ordered anti-clockwise. When ordered in a clockwise fashion, the
result was correct but negative.

Refer to https://www.mathopenref.com/coordpolygonarea2.html
for more information.

libs/kimath/src/geometry/shape_line_chain.cpp

@@ -1714,7 +1714,7 @@ double SHAPE_LINE_CHAIN::Area() const
         j = i;
     }
 
-    return -area * 0.5;
+    return std::fabs( area * 0.5 ); // The result would be negative if points are anti-clockwise
 }
 
 

pcbnew/dialogs/dialog_board_statistics.cpp

@@ -323,13 +323,13 @@ void DIALOG_BOARD_STATISTICS::getDataFromPCB()
         for( int i = 0; i < polySet.OutlineCount(); i++ )
         {
             SHAPE_LINE_CHAIN& outline = polySet.Outline( i );
-            m_boardArea += std::fabs( outline.Area() );
+            m_boardArea += outline.Area();
 
             // If checkbox "subtract holes" is checked
             if( m_checkBoxSubtractHoles->GetValue() )
             {
                 for( int j = 0; j < polySet.HoleCount( i ); j++ )
-                    m_boardArea -= std::fabs( polySet.Hole( i, j ).Area() );
+                    m_boardArea -= polySet.Hole( i, j ).Area();
             }
 
             if( boundingBoxCreated )

pcbnew/router/pns_mouse_trail_tracer.cpp

@@ -119,7 +119,7 @@ DIRECTION_45 MOUSE_TRAIL_TRACER::GetPosture( const VECTOR2I& aP )
 
     PNS_DBG( dbg, AddLine, straight, m_forced ? BLUE : GREEN, 100000, "mt-straight" );
 
-    double areaS = std::abs( straight.Area() );
+    double areaS = straight.Area();
 
     SHAPE_LINE_CHAIN diag( DIRECTION_45().BuildInitialTrace( p0, aP, true, false ) );
     diag.Append( m_trail.Reverse() );
@@ -128,7 +128,7 @@ DIRECTION_45 MOUSE_TRAIL_TRACER::GetPosture( const VECTOR2I& aP )
 
     PNS_DBG( dbg, AddLine, diag, YELLOW, 100000, "mt-diag" );
 
-    double areaDiag = std::abs( diag.Area() );
+    double areaDiag = diag.Area();
     double ratio    = areaS / ( areaDiag + 1.0 );
 
     // heuristic to detect that the user dragged back the cursor to the beginning of the trace
@@ -152,7 +152,7 @@ DIRECTION_45 MOUSE_TRAIL_TRACER::GetPosture( const VECTOR2I& aP )
         SHAPE_LINE_CHAIN trail( m_trail );
         trail.SetClosed( true );
 
-        if( std::abs( trail.Area() ) > areaCutoff )
+        if( trail.Area() > areaCutoff )
             areaOk = true;
 }