From 6eeca9aa90cbb5550f9030cf280af16cd1e3aede Mon Sep 17 00:00:00 2001
From: jean-pierre charras <jp.charras@wanadoo.fr>
Date: Wed, 13 Sep 2023 17:54:57 +0200
Subject: [PATCH] Pcbnew: fix some issues with very small arcs (size a few
 internal units) these very small arcs do not allow to calculate a reliable
 center position, and therefore a reliable radius. So handle them as a very
 small segments to fix plotting/drawing issues. From master branch. Fixes
 #15639 https://gitlab.com/kicad/code/kicad/-/issues/15639

---
 .../3d_canvas/create_3Dgraphic_brd_items.cpp  | 13 ++++++++++
 pcbnew/pcb_track.cpp                          | 11 ++++++++
 pcbnew/pcb_track.h                            |  8 ++++++
 pcbnew/plot_board_layers.cpp                  | 25 +++++++++++++------
 4 files changed, 50 insertions(+), 7 deletions(-)

diff --git a/3d-viewer/3d_canvas/create_3Dgraphic_brd_items.cpp b/3d-viewer/3d_canvas/create_3Dgraphic_brd_items.cpp
index 21abc51d43..f11799c6db 100644
--- a/3d-viewer/3d_canvas/create_3Dgraphic_brd_items.cpp
+++ b/3d-viewer/3d_canvas/create_3Dgraphic_brd_items.cpp
@@ -261,6 +261,19 @@ void BOARD_ADAPTER::createTrack( const PCB_TRACK* aTrack, CONTAINER_2D_BASE* aDs
     {
         const PCB_ARC* arc = static_cast<const PCB_ARC*>( aTrack );
 
+        if( arc->IsDegenerated() )
+        {
+            // Draw this very small arc like a track segment (a PCB_TRACE_T)
+            PCB_TRACK track( arc->GetParent() );
+            track.SetStart( arc->GetStart() );
+            track.SetEnd( arc->GetEnd() );
+            track.SetWidth( arc->GetWidth() );
+            track.SetLayer( arc->GetLayer() );
+
+            createTrack( &track, aDstContainer );
+            return;
+        }
+
         VECTOR2D  center( arc->GetCenter() );
         EDA_ANGLE arc_angle = arc->GetAngle();
         double    radius = arc->GetRadius();
diff --git a/pcbnew/pcb_track.cpp b/pcbnew/pcb_track.cpp
index 84a9089919..425ad6a9aa 100644
--- a/pcbnew/pcb_track.cpp
+++ b/pcbnew/pcb_track.cpp
@@ -1170,6 +1170,17 @@ EDA_ANGLE PCB_ARC::GetArcAngleEnd() const
     return angleEnd.Normalize();
 }
 
+bool PCB_ARC::IsDegenerated( int aThreshold ) const
+{
+    // Too small arcs cannot be really handled: arc center (and arc radius)
+    // cannot be safely computed if the distance between mid and end points
+    // is too small (a few internal units)
+
+    // len of both segments must be < aThreshold to be a very small degenerated arc
+    return ( GetMid() - GetStart() ).EuclideanNorm() < aThreshold
+            && ( GetMid() - GetEnd() ).EuclideanNorm() < aThreshold;
+}
+
 
 bool PCB_TRACK::cmp_tracks::operator() ( const PCB_TRACK* a, const PCB_TRACK* b ) const
 {
diff --git a/pcbnew/pcb_track.h b/pcbnew/pcb_track.h
index d65e03443d..43edbe782f 100644
--- a/pcbnew/pcb_track.h
+++ b/pcbnew/pcb_track.h
@@ -357,6 +357,14 @@ public:
 
     EDA_ITEM* Clone() const override;
 
+    /**
+     * @return true if the arc is too small to allow a safe calculation
+     * of center position and arc angles i.e if distance between m_Mid and each arc end
+     * is only a few internal units.
+     * @param aThreshold is the minimal dist in internal units. Default id 5 IU
+     */
+    bool IsDegenerated( int aThreshold = 5 ) const;
+
 protected:
     virtual void swapData( BOARD_ITEM* aImage ) override;
 
diff --git a/pcbnew/plot_board_layers.cpp b/pcbnew/plot_board_layers.cpp
index a1580764a3..f23d1eca5e 100644
--- a/pcbnew/plot_board_layers.cpp
+++ b/pcbnew/plot_board_layers.cpp
@@ -638,17 +638,28 @@ void PlotStandardLayer( BOARD* aBoard, PLOTTER* aPlotter, LSET aLayerMask,
         {
             const     PCB_ARC* arc = static_cast<const PCB_ARC*>( track );
 
-            // ThickArc expects only positive angle arcs, so flip start/end if
-            // we are negative
-            if( arc->GetAngle() < ANGLE_0 )
+            // Too small arcs cannot be really handled: arc center (and arc radius)
+            // cannot be safely computed
+            if( arc->IsDegenerated( 10 /* in IU */ ) )
             {
-                aPlotter->ThickArc( arc->GetCenter(), arc->GetEnd(), arc->GetStart(),
-                                    width, plotMode, &gbr_metadata );
+                // Approximate this very small arc by a segment.
+                aPlotter->ThickSegment( track->GetStart(), track->GetEnd(), width, plotMode,
+                                        &gbr_metadata );
             }
             else
             {
-                aPlotter->ThickArc( arc->GetCenter(), arc->GetStart(), arc->GetEnd(),
-                                    width, plotMode, &gbr_metadata );
+                // ThickArc expects only positive angle arcs, so flip start/end if
+                // we are negative
+                if( arc->GetAngle() < ANGLE_0 )
+                {
+                    aPlotter->ThickArc( arc->GetCenter(), arc->GetEnd(), arc->GetStart(),
+                                        width, plotMode, &gbr_metadata );
+                }
+                else
+                {
+                    aPlotter->ThickArc( arc->GetCenter(), arc->GetStart(), arc->GetEnd(),
+                                        width, plotMode, &gbr_metadata );
+                }
             }
         }
         else