From 407301a28c4b31c450b0653f54b5336ff5840977 Mon Sep 17 00:00:00 2001
From: jean-pierre charras <jp.charras@wanadoo.fr>
Date: Sun, 9 Jun 2019 11:06:00 +0200
Subject: [PATCH] Fix issue in cairo_gal when drawing a 360 deg arc (in fact a
 circle). It was due to a angle normalization between -360 and 360 degrees.
 So, in arcs, if the start angle and end angle diff is n*360 deg, this
 normalization gives start angle = end angle. The fix forces end angle = start
 angle+360deg in this case.

Fixes: lp:1832096
https://bugs.launchpad.net/kicad/+bug/1832096
---
 common/gal/cairo/cairo_gal.cpp | 12 +++++++++++-
 gerbview/gerbview_painter.cpp  | 20 ++++++++++----------
 2 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/common/gal/cairo/cairo_gal.cpp b/common/gal/cairo/cairo_gal.cpp
index 81939c2a13..80e1223691 100644
--- a/common/gal/cairo/cairo_gal.cpp
+++ b/common/gal/cairo/cairo_gal.cpp
@@ -146,8 +146,18 @@ void CAIRO_GAL_BASE::arc_angles_xform_and_normalize( double& aStartAngle, double
     SWAP( startAngle, >, endAngle );
 
     // now rotate arc according to the rotation transform matrix
+    // Remark:
+    // We call angle_xform() to calculate angles according to the flip/rotation
+    // transform and normatize between -2M_PI and +2M_PI.
+    // Therefore, if aStartAngle = aEndAngle + 2*n*M_PI, the transform gives
+    // aEndAngle = aStartAngle
+    // So, if this is the case, force the aEndAngle value to draw a circle.
     aStartAngle = angle_xform( startAngle );
-    aEndAngle = angle_xform( endAngle );
+
+    if( std::abs( aEndAngle - aStartAngle ) >= 2*M_PI )     // arc is a full circle
+        aEndAngle = aStartAngle + 2*M_PI;
+    else
+        aEndAngle = angle_xform( endAngle );
 }
 
 
diff --git a/gerbview/gerbview_painter.cpp b/gerbview/gerbview_painter.cpp
index 752b6d0e41..7920d30b25 100644
--- a/gerbview/gerbview_painter.cpp
+++ b/gerbview/gerbview_painter.cpp
@@ -2,7 +2,7 @@
  * This program source code file is part of KiCad, a free EDA CAD application.
  *
  * Copyright (C) 2017 Jon Evans <jon@craftyjon.com>
- * Copyright (C) 2017 KiCad Developers, see AUTHORS.txt for contributors.
+ * Copyright (C) 2019 KiCad Developers, see AUTHORS.txt for contributors.
  *
  * This program is free software: you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the
@@ -315,21 +315,21 @@ void GERBVIEW_PAINTER::draw( /*const*/ GERBER_DRAW_ITEM* aItem, int aLayer )
         if( startAngle > endAngle )
             endAngle += (2 * M_PI);
 
-        // 360-degree arcs are stored in the file with start equal to end
+        // In Gerber, 360-degree arcs are stored in the file with start equal to end
         if( arcStart == arcEnd )
         {
-            startAngle = 0;
-            endAngle = 2 * M_PI;
+            endAngle =  startAngle + 2*M_PI;
         }
 
         m_gal->DrawArcSegment( center, radius, startAngle, endAngle, width );
 
-        // Arc Debugging
-        // m_gal->SetLineWidth( 5 );
-        // m_gal->SetStrokeColor( COLOR4D( 0.0, 1.0, 0.0, 1.0 ) );
-        // m_gal->DrawLine( center, aItem->GetABPosition( arcStart ) );
-        // m_gal->SetStrokeColor( COLOR4D( 1.0, 0.0, 0.0, 1.0 ) );
-        // m_gal->DrawLine( center, aItem->GetABPosition( arcEnd ) );
+#if 0   // Arc Debugging only
+        m_gal->SetLineWidth( 5 );
+        m_gal->SetStrokeColor( COLOR4D( 0.0, 1.0, 0.0, 1.0 ) );
+        m_gal->DrawLine( center, aItem->GetABPosition( arcStart ) );
+        m_gal->SetStrokeColor( COLOR4D( 1.0, 0.0, 0.0, 1.0 ) );
+        m_gal->DrawLine( center, aItem->GetABPosition( arcEnd ) );
+#endif
         break;
     }