Implement shoving of free vias.

Also contains a little bit of cleanup and a lot of commenting.

Fixes: lp:1833216
* https://bugs.launchpad.net/kicad/+bug/1833216

Fixes: lp:1833214
* https://bugs.launchpad.net/kicad/+bug/1833214

pcbnew/router/pns_item.cpp

@@ -2,7 +2,7 @@
  * KiRouter - a push-and-(sometimes-)shove PCB router
  *
  * Copyright (C) 2013-2014 CERN
- * Copyright (C) 2016 KiCad Developers, see AUTHORS.txt for contributors.
+ * Copyright (C) 2016-2019 KiCad Developers, see AUTHORS.txt for contributors.
  * Author: Tomasz Wlostowski <tomasz.wlostowski@cern.ch>
  *
  * This program is free software: you can redistribute it and/or modify it
@@ -19,12 +19,7 @@
  * with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include <class_board.h>
-#include <class_board_item.h>
-#include <class_pad.h>
-#include <class_track.h>    // For ::VIA
-#include <pad_shapes.h>
-
+#include "pns_node.h"
 #include "pns_item.h"
 #include "pns_line.h"
 
@@ -32,72 +27,12 @@ typedef VECTOR2I::extended_type ecoord;
 
 namespace PNS {
 
-static int holeRadius( BOARD_ITEM* aItem )
-{
-    if( aItem->Type() == PCB_PAD_T )
-    {
-        const D_PAD* pad = static_cast<const D_PAD*>( aItem );
-
-        if( pad->GetDrillSize().x && pad->GetDrillShape() == PAD_DRILL_SHAPE_CIRCLE )
-            return pad->GetDrillSize().x / 2;
-        else
-            return 0;
-    }
-    else if( aItem->Type() == PCB_VIA_T )
-    {
-        return static_cast<const ::VIA*>( aItem )->GetDrillValue() / 2;
-    }
-
-    return 0;
-}
-
-
-bool ITEM::CollideHoles( const ITEM* aOther, bool aNeedMTV, VECTOR2I& aMTV ) const
-{
-    BOARD_ITEM* a = Parent();
-    BOARD_ITEM* b = aOther->Parent();
-
-    if( !a || !b )
-        return false;
-
-    // Holes with identical locations are allowable
-    if( a->GetPosition() == b->GetPosition() )
-        return false;
-
-    int radius_a = holeRadius( a );
-    int radius_b = holeRadius( b );
-
-    // Do both objects have holes?
-    if( radius_a > 0 && radius_b > 0 )
-    {
-        int holeToHoleMin = a->GetBoard()->GetDesignSettings().m_HoleToHoleMin;
-
-        ecoord min_dist = holeToHoleMin + radius_a + radius_b;
-        ecoord min_dist_sq = min_dist * min_dist;
-
-        const VECTOR2I delta = b->GetPosition() - a->GetPosition();
-
-        ecoord dist_sq = delta.SquaredEuclideanNorm();
-
-        if( dist_sq < min_dist_sq )
-        {
-            if( aNeedMTV )
-                aMTV = delta.Resize( min_dist - sqrt( dist_sq ) + 3 );  // fixme: apparent rounding error
-
-            return true;
-        }
-    }
-
-    return false;
-}
-
-
-bool ITEM::collideSimple( const ITEM* aOther, int aClearance, bool aNeedMTV, VECTOR2I& aMTV,
-                          bool aDifferentNetsOnly ) const
+bool ITEM::collideSimple( const ITEM* aOther, int aClearance, bool aNeedMTV, VECTOR2I* aMTV,
+                          const NODE* aParentNode, bool aDifferentNetsOnly ) const
 {
     // hole-to-hole is a mechanical constraint (broken drill bits) not an electrical one, so
     // it must be checked before checking aDifferentNetsOnly
-    if( CollideHoles( aOther, aNeedMTV, aMTV ) )
+    if( aParentNode->GetRuleResolver()->CollideHoles( this, aOther, aNeedMTV, aMTV ) )
         return true;
 
     // same nets? no collision!
@@ -108,14 +43,17 @@ bool ITEM::collideSimple( const ITEM* aOther, int aClearance, bool aNeedMTV, VEC
     if( !m_layers.Overlaps( aOther->m_layers ) )
         return false;
 
-    return Shape()->Collide( aOther->Shape(), aClearance, aMTV );
+    if( aNeedMTV )
+        return Shape()->Collide( aOther->Shape(), aClearance, *aMTV );
+    else
+        return Shape()->Collide( aOther->Shape(), aClearance );
 }
 
 
-bool ITEM::Collide( const ITEM* aOther, int aClearance, bool aNeedMTV, VECTOR2I& aMTV,
-                    bool aDifferentNetsOnly ) const
+bool ITEM::Collide( const ITEM* aOther, int aClearance, bool aNeedMTV, VECTOR2I* aMTV,
+                    const NODE* aParentNode, bool aDifferentNetsOnly ) const
 {
-    if( collideSimple( aOther, aClearance, aNeedMTV, aMTV, aDifferentNetsOnly ) )
+    if( collideSimple( aOther, aClearance, aNeedMTV, aMTV, aParentNode, aDifferentNetsOnly ) )
         return true;
 
     // special case for "head" line with a via attached at the end.
@@ -125,7 +63,10 @@ bool ITEM::Collide( const ITEM* aOther, int aClearance, bool aNeedMTV, VECTOR2I&
         int clearance = aClearance - line->Width() / 2;
 
         if( line->EndsWithVia() )
-            return collideSimple( &line->Via(), clearance, aNeedMTV, aMTV, aDifferentNetsOnly );
+        {
+            return collideSimple( &line->Via(), clearance, aNeedMTV, aMTV, aParentNode,
+                                  aDifferentNetsOnly );
+        }
     }
 
     return false;

pcbnew/router/pns_item.h

@@ -201,26 +201,8 @@ public:
      * @param aMTV the minimum translation vector
      * @return true, if a collision was found.
      */
-    virtual bool Collide( const ITEM* aOther, int aClearance, bool aNeedMTV, VECTOR2I& aMTV,
-                          bool aDifferentNetsOnly = true ) const;
-
-    /**
-     * Function CollideHoles()
-     *
-     * Similar to Collide(), above, but checks for hole-to-hole-minimum violations.
-     */
-    bool CollideHoles( const ITEM* aOther, bool aNeedMTV, VECTOR2I& aMTV ) const;
-
-    /**
-     * Function Collide()
-     *
-     * A shortcut for ITEM::Colllide() without MTV stuff.
-     */
-  	bool Collide( const ITEM* aOther, int aClearance, bool aDifferentNetsOnly = true ) const
-    {
-        VECTOR2I dummy;
-        return Collide( aOther, aClearance, false, dummy, aDifferentNetsOnly );
-    }
+    virtual bool Collide( const ITEM* aOther, int aClearance, bool aNeedMTV, VECTOR2I* aMTV,
+                          const NODE* aParentNode, bool aDifferentNetsOnly = true ) const;
 
     /**
      * Function Shape()
@@ -259,8 +241,8 @@ public:
     bool IsRoutable() const { return m_routable; }
 
 private:
-    bool collideSimple( const ITEM* aOther, int aClearance, bool aNeedMTV,
-                        VECTOR2I& aMTV, bool aDifferentNetsOnly ) const;
+    bool collideSimple( const ITEM* aOther, int aClearance, bool aNeedMTV, VECTOR2I* aMTV,
+                        const NODE* aParentNode, bool aDifferentNetsOnly ) const;
 
 protected:
     PnsKind                 m_kind;

pcbnew/router/pns_kicad_iface.cpp

@@ -60,17 +60,23 @@
 #include "pns_debug_decorator.h"
 #include "router_preview_item.h"
 
+typedef VECTOR2I::extended_type ecoord;
+
 class PNS_PCBNEW_RULE_RESOLVER : public PNS::RULE_RESOLVER
 {
 public:
     PNS_PCBNEW_RULE_RESOLVER( BOARD* aBoard, PNS::ROUTER* aRouter );
     virtual ~PNS_PCBNEW_RULE_RESOLVER();
 
+    virtual bool CollideHoles( const PNS::ITEM* aA, const PNS::ITEM* aB,
+                               bool aNeedMTV, VECTOR2I* aMTV ) const override;
+
     virtual int Clearance( const PNS::ITEM* aA, const PNS::ITEM* aB ) const override;
     virtual int Clearance( int aNetCode ) const override;
     virtual int DpCoupledNet( int aNet ) override;
     virtual int DpNetPolarity( int aNet ) override;
     virtual bool DpNetPair( PNS::ITEM* aItem, int& aNetP, int& aNetN ) override;
+
     virtual wxString NetName( int aNet ) override;
 
 private:
@@ -81,6 +87,7 @@ private:
         int clearance;
     };
 
+    int holeRadius( const PNS::ITEM* aItem ) const;
     int localPadClearance( const PNS::ITEM* aItem ) const;
     int matchDpSuffix( const wxString& aNetName, wxString& aComplementNet, wxString& aBaseDpName );
 
@@ -160,6 +167,65 @@ PNS_PCBNEW_RULE_RESOLVER::~PNS_PCBNEW_RULE_RESOLVER()
 }
 
 
+int PNS_PCBNEW_RULE_RESOLVER::holeRadius( const PNS::ITEM* aItem ) const
+{
+    if( aItem->Kind() == PNS::ITEM::SOLID_T )
+    {
+        const D_PAD* pad = dynamic_cast<const D_PAD*>( aItem->Parent() );
+
+        if( pad && pad->GetDrillShape() == PAD_DRILL_SHAPE_CIRCLE )
+            return pad->GetDrillSize().x / 2;
+    }
+    else if( aItem->Kind() == PNS::ITEM::VIA_T )
+    {
+        const ::VIA* via = dynamic_cast<const ::VIA*>( aItem->Parent() );
+
+        if( via )
+            return via->GetDrillValue() / 2;
+    }
+
+    return 0;
+}
+
+
+bool PNS_PCBNEW_RULE_RESOLVER::CollideHoles( const PNS::ITEM* aA, const PNS::ITEM* aB,
+                                             bool aNeedMTV, VECTOR2I* aMTV ) const
+{
+    VECTOR2I pos_a = aA->Shape()->Centre();
+    VECTOR2I pos_b = aB->Shape()->Centre();
+
+    // Holes with identical locations are allowable
+    if( pos_a == pos_b )
+        return false;
+
+    int radius_a = holeRadius( aA );
+    int radius_b = holeRadius( aB );
+
+    // Do both objects have holes?
+    if( radius_a > 0 && radius_b > 0 )
+    {
+        int holeToHoleMin = m_board->GetDesignSettings().m_HoleToHoleMin;
+
+        ecoord min_dist = holeToHoleMin + radius_a + radius_b;
+        ecoord min_dist_sq = min_dist * min_dist;
+
+        const VECTOR2I delta = pos_b - pos_a;
+
+        ecoord dist_sq = delta.SquaredEuclideanNorm();
+
+        if( dist_sq < min_dist_sq )
+        {
+            if( aNeedMTV )
+                *aMTV = delta.Resize( min_dist - sqrt( dist_sq ) + 3 );  // fixme: apparent rounding error
+
+            return true;
+        }
+    }
+
+    return false;
+}
+
+
 int PNS_PCBNEW_RULE_RESOLVER::localPadClearance( const PNS::ITEM* aItem ) const
 {
     if( !aItem->Parent() || aItem->Parent()->Type() != PCB_PAD_T )

pcbnew/router/pns_node.cpp

@@ -234,7 +234,7 @@ struct NODE::DEFAULT_OBSTACLE_VISITOR : public OBSTACLE_VISITOR
         if( m_forceClearance >= 0 )
             clearance = m_forceClearance;
 
-        if( !aCandidate->Collide( m_item, clearance, m_differentNetsOnly ) )
+        if( !aCandidate->Collide( m_item, clearance, false, nullptr, m_node, m_differentNetsOnly ) )
             return true;
 
         OBSTACLE obs;
@@ -269,8 +269,8 @@ int NODE::QueryColliding( const ITEM* aItem, OBSTACLE_VISITOR& aVisitor )
 }
 
 
-int NODE::QueryColliding( const ITEM* aItem,
-        NODE::OBSTACLES& aObstacles, int aKindMask, int aLimitCount, bool aDifferentNetsOnly, int aForceClearance )
+int NODE::QueryColliding( const ITEM* aItem, NODE::OBSTACLES& aObstacles, int aKindMask,
+                          int aLimitCount, bool aDifferentNetsOnly, int aForceClearance )
 {
     DEFAULT_OBSTACLE_VISITOR visitor( aObstacles, aItem, aKindMask, aDifferentNetsOnly );
 
@@ -469,7 +469,7 @@ bool NODE::CheckColliding( const ITEM* aItemA, const ITEM* aItemB, int aKindMask
     if( aItemB->Kind() == ITEM::LINE_T )
         clearance += static_cast<const LINE*>( aItemB )->Width() / 2;
 
-    return aItemA->Collide( aItemB, clearance );
+    return aItemA->Collide( aItemB, clearance, false, nullptr, this );
 }
 
 
@@ -608,22 +608,11 @@ void NODE::Add( std::unique_ptr< ITEM > aItem, bool aAllowRedundant )
 {
     switch( aItem->Kind() )
     {
-    case ITEM::SOLID_T:
-        Add( ItemCast<SOLID>( std::move( aItem ) ) );
-        break;
-
-    case ITEM::SEGMENT_T:
-        Add( ItemCast<SEGMENT>( std::move( aItem ) ), aAllowRedundant );
-        break;
+    case ITEM::SOLID_T:   Add( ItemCast<SOLID>( std::move( aItem ) ) );                    break;
+    case ITEM::SEGMENT_T: Add( ItemCast<SEGMENT>( std::move( aItem ) ), aAllowRedundant ); break;
+    case ITEM::VIA_T:     Add( ItemCast<VIA>( std::move( aItem ) ) );                      break;
 
     case ITEM::LINE_T:
-        assert( false );
-        break;
-
-    case ITEM::VIA_T:
-        Add( ItemCast<VIA>( std::move( aItem ) ) );
-        break;
-
     default:
         assert( false );
     }
@@ -660,7 +649,8 @@ void NODE::removeSegmentIndex( SEGMENT* aSeg )
 void NODE::removeViaIndex( VIA* aVia )
 {
     // We have to split a single joint (associated with a via, binding together multiple layers)
-    // into multiple independent joints. As I'm a lazy bastard, I simply delete the via and all its links and re-insert them.
+    // into multiple independent joints. As I'm a lazy bastard, I simply delete the via and all
+    // its links and re-insert them.
 
     JOINT::HASH_TAG tag;
 
@@ -1258,36 +1248,18 @@ void NODE::ClearRanks( int aMarkerMask )
 }
 
 
-int NODE::FindByMarker( int aMarker, ITEM_SET& aItems )
-{
-    for( INDEX::ITEM_SET::iterator i = m_index->begin(); i != m_index->end(); ++i )
-    {
-        if( (*i)->Marker() & aMarker )
-            aItems.Add( *i );
-    }
-
-    return 0;
-}
-
-
-int NODE::RemoveByMarker( int aMarker )
+void NODE::RemoveByMarker( int aMarker )
 {
     std::list<ITEM*> garbage;
 
-    for( INDEX::ITEM_SET::iterator i = m_index->begin(); i != m_index->end(); ++i )
-    {
-        if( (*i)->Marker() & aMarker )
-        {
-            garbage.push_back( *i );
-        }
-    }
-
-    for( std::list<ITEM*>::const_iterator i = garbage.begin(), end = garbage.end(); i != end; ++i )
+    for( ITEM* item : *m_index )
     {
-        Remove( *i );
+        if( item->Marker() & aMarker )
+            garbage.push_back( item );
     }
 
-    return 0;
+    for( ITEM* item : garbage )
+        Remove( item );
 }
 
 SEGMENT* NODE::findRedundantSegment( const VECTOR2I& A, const VECTOR2I& B, const LAYER_RANGE& lr,

pcbnew/router/pns_node.h

@@ -58,11 +58,15 @@ class RULE_RESOLVER
 public:
     virtual ~RULE_RESOLVER() {}
 
+    virtual bool CollideHoles( const ITEM* aA, const ITEM* aB,
+                               bool aNeedMTV, VECTOR2I* aMTV ) const = 0;
+
     virtual int Clearance( const ITEM* aA, const ITEM* aB ) const = 0;
     virtual int Clearance( int aNetCode ) const = 0;
     virtual int DpCoupledNet( int aNet ) = 0;
     virtual int DpNetPolarity( int aNet ) = 0;
     virtual bool DpNetPair( ITEM* aItem, int& aNetP, int& aNetN ) = 0;
+
     virtual wxString NetName( int aNet ) = 0;
 };
 
@@ -164,7 +168,7 @@ public:
         m_ruleResolver = aFunc;
     }
 
-    RULE_RESOLVER* GetRuleResolver()
+    RULE_RESOLVER* GetRuleResolver() const
     {
         return m_ruleResolver;
     }
@@ -401,8 +405,7 @@ public:
 
     void ClearRanks( int aMarkerMask = MK_HEAD | MK_VIOLATION );
 
-    int FindByMarker( int aMarker, ITEM_SET& aItems );
-    int RemoveByMarker( int aMarker );
+    void RemoveByMarker( int aMarker );
 
     ITEM* FindItemByParent( const BOARD_CONNECTED_ITEM* aParent );
 

pcbnew/router/pns_optimizer.cpp

@@ -154,7 +154,7 @@ struct OPTIMIZER::CACHE_VISITOR
 
         int clearance = m_node->GetClearance( aOtherItem, m_ourItem );
 
-        if( !aOtherItem->Collide( m_ourItem, clearance ) )
+        if( !aOtherItem->Collide( m_ourItem, clearance, false, nullptr, m_node ) )
             return true;
 
         m_collidingItem = aOtherItem;

pcbnew/router/pns_shove.cpp

@@ -35,6 +35,9 @@
 
 #include "time_limit.h"
 
+
+typedef VECTOR2I::extended_type ecoord;
+
 namespace PNS {
 
 void SHOVE::replaceItems( ITEM* aOld, std::unique_ptr< ITEM > aNew )
@@ -149,6 +152,9 @@ SHOVE::SHOVE_STATUS SHOVE::walkaroundLoneVia( LINE& aCurrent, LINE& aObstacle, L
 }
 
 
+/*
+ * TODO describe....
+ */
 SHOVE::SHOVE_STATUS SHOVE::processHullSet( LINE& aCurrent, LINE& aObstacle,
                                                    LINE& aShoved, const HULL_SET& aHulls )
 {
@@ -249,6 +255,9 @@ SHOVE::SHOVE_STATUS SHOVE::processHullSet( LINE& aCurrent, LINE& aObstacle,
 }
 
 
+/*
+ * TODO describe....
+ */
 SHOVE::SHOVE_STATUS SHOVE::ProcessSingleLine( LINE& aCurrent, LINE& aObstacle, LINE& aShoved )
 {
     aShoved.ClearSegmentLinks();
@@ -304,6 +313,9 @@ SHOVE::SHOVE_STATUS SHOVE::ProcessSingleLine( LINE& aCurrent, LINE& aObstacle, L
 }
 
 
+/*
+ * TODO describe....
+ */
 SHOVE::SHOVE_STATUS SHOVE::onCollidingSegment( LINE& aCurrent, SEGMENT* aObstacleSeg )
 {
     int segIndex;
@@ -362,6 +374,9 @@ SHOVE::SHOVE_STATUS SHOVE::onCollidingSegment( LINE& aCurrent, SEGMENT* aObstacl
 }
 
 
+/*
+ * TODO describe....
+ */
 SHOVE::SHOVE_STATUS SHOVE::onCollidingLine( LINE& aCurrent, LINE& aObstacle )
 {
     LINE shovedLine( aObstacle );
@@ -401,6 +416,10 @@ SHOVE::SHOVE_STATUS SHOVE::onCollidingLine( LINE& aCurrent, LINE& aObstacle )
     return rv;
 }
 
+
+/*
+ * TODO describe....
+ */
 SHOVE::SHOVE_STATUS SHOVE::onCollidingSolid( LINE& aCurrent, ITEM* aObstacle )
 {
     WALKAROUND walkaround( m_currentNode, Router() );
@@ -586,6 +605,10 @@ bool SHOVE::pushSpringback( NODE* aNode, const OPT_BOX2I& aAffectedArea, VIA* aD
 }
 
 
+/*
+ * Push or shove a via by at least aForce.  (The via might be pushed or shoved slightly further
+ * to keep it from landing on an existing joint.)
+ */
 SHOVE::SHOVE_STATUS SHOVE::pushOrShoveVia( VIA* aVia, const VECTOR2I& aForce, int aCurrentRank )
 {
     LINE_PAIR_VEC draggedLines;
@@ -659,8 +682,15 @@ SHOVE::SHOVE_STATUS SHOVE::pushOrShoveVia( VIA* aVia, const VECTOR2I& aForce, in
     m_logger.Log( pushedVia.get(), 1, "pushed-via" );
 #endif
 
-    if( aVia->Marker() & MK_HEAD )
+    if( aVia->Marker() & MK_HEAD )      // push
+    {
         m_draggedVia = pushedVia.get();
+    }
+    else
+    {                                   // shove
+        if( jt->IsStitchingVia() )
+            pushLineStack( LINE( *pushedVia ) );
+    }
 
     replaceItems( aVia, std::move( pushedVia ) );
 
@@ -701,17 +731,24 @@ SHOVE::SHOVE_STATUS SHOVE::pushOrShoveVia( VIA* aVia, const VECTOR2I& aForce, in
 }
 
 
+/*
+ * Calculate the minimum translation vector required to resolve a collision with a via and
+ * shove the via by that distance.
+ */
 SHOVE::SHOVE_STATUS SHOVE::onCollidingVia( ITEM* aCurrent, VIA* aObstacleVia )
 {
+    RULE_RESOLVER* rr = m_currentNode->GetRuleResolver();
     int clearance = getClearance( aCurrent, aObstacleVia ) ;
     LINE_PAIR_VEC draggedLines;
     bool lineCollision = false;
     bool viaCollision = false;
+    bool holeCollision = false;
     LINE* currentLine = NULL;
-    VECTOR2I mtvLine;
-    VECTOR2I mtvVia;
-    VECTOR2I mtvSolid;
-    VECTOR2I mtv;
+    VECTOR2I mtvLine;       // Minimum translation vector to correct line collisions
+    VECTOR2I mtvVia;        // MTV to correct via collisions
+    VECTOR2I mtvHoles;      // MTV to correct hole collisions
+    VECTOR2I mtvSolid;      // MTV to correct solid collisions
+    VECTOR2I mtv;           // Union of relevant MTVs (will correct all collisions)
     int rank = -1;
 
     if( aCurrent->OfKind( ITEM::LINE_T ) )
@@ -728,19 +765,32 @@ SHOVE::SHOVE_STATUS SHOVE::onCollidingVia( ITEM* aCurrent, VIA* aObstacleVia )
 
         if( currentLine->EndsWithVia() )
         {
-            viaCollision = CollideShapes( currentLine->Via().Shape(), aObstacleVia->Shape(),
-                                          clearance + PNS_HULL_MARGIN, true, mtvVia );
+            int currentNet = currentLine->Net();
+            int obstacleNet = aObstacleVia->Net();
+
+            if( currentNet != obstacleNet && currentNet >= 0 && obstacleNet >= 0 )
+            {
+                viaCollision = CollideShapes( currentLine->Via().Shape(), aObstacleVia->Shape(),
+                                              clearance + PNS_HULL_MARGIN, true, mtvVia );
+            }
+
+            // hole-to-hole is a mechanical constraint (broken drill bits), not an electrical
+            // one, so it has to be checked irrespective of matching nets.
+            holeCollision = rr->CollideHoles( &currentLine->Via(), aObstacleVia, true, &mtvHoles );
         }
 
-        if( !lineCollision && !viaCollision )
-             return SH_OK;
+        // These aren't /actually/ lengths as we don't bother to do the square-root part,
+        // but we're just comparing them to each other so it's faster this way.
+        ecoord lineMTVLength = lineCollision ? mtvLine.SquaredEuclideanNorm() : 0;
+        ecoord viaMTVLength = viaCollision ? mtvVia.SquaredEuclideanNorm() : 0;
+        ecoord holeMTVLength = holeCollision ? mtvHoles.SquaredEuclideanNorm() : 0;
 
-        if( lineCollision && viaCollision )
-            mtv = mtvVia.EuclideanNorm() > mtvLine.EuclideanNorm() ? mtvVia : mtvLine;
-        else if( lineCollision )
+        if( lineMTVLength >= viaMTVLength && lineMTVLength >= holeMTVLength )
             mtv = mtvLine;
-        else
+        else if( viaMTVLength >= lineMTVLength && viaMTVLength >= holeMTVLength )
             mtv = mtvVia;
+        else
+            mtv = mtvHoles;
 
         rank = currentLine->Rank();
     }
@@ -756,6 +806,9 @@ SHOVE::SHOVE_STATUS SHOVE::onCollidingVia( ITEM* aCurrent, VIA* aObstacleVia )
 }
 
 
+/*
+ * TODO describe....
+ */
 SHOVE::SHOVE_STATUS SHOVE::onReverseCollidingVia( LINE& aCurrent, VIA* aObstacleVia )
 {
     int n = 0;
@@ -918,6 +971,9 @@ void SHOVE::popLineStack( )
 }
 
 
+/*
+ * Resolve the next collision.
+ */
 SHOVE::SHOVE_STATUS SHOVE::shoveIteration( int aIter )
 {
     LINE currentLine = m_lineStack.back();
@@ -944,20 +1000,22 @@ SHOVE::SHOVE_STATUS SHOVE::shoveIteration( int aIter )
 
     if( !ni->OfKind( ITEM::SOLID_T ) && ni->Rank() >= 0 && ni->Rank() > currentLine.Rank() )
     {
+        // Collision with a higher-ranking object (ie: one that we've already shoved)
+        //
         switch( ni->Kind() )
         {
         case ITEM::VIA_T:
         {
-            VIA* revVia = (VIA*) ni;
             wxLogTrace( "PNS", "iter %d: reverse-collide-via", aIter );
 
-            if( currentLine.EndsWithVia() && m_currentNode->CheckColliding( &currentLine.Via(), revVia ) )
+            if( currentLine.EndsWithVia()
+                    && m_currentNode->CheckColliding( &currentLine.Via(), (VIA*) ni ) )
             {
                 st = SH_INCOMPLETE;
             }
             else
             {
-                st = onReverseCollidingVia( currentLine, revVia );
+                st = onReverseCollidingVia( currentLine, (VIA*) ni );
             }
 
             break;
@@ -965,9 +1023,8 @@ SHOVE::SHOVE_STATUS SHOVE::shoveIteration( int aIter )
 
         case ITEM::SEGMENT_T:
         {
-            SEGMENT* seg = (SEGMENT*) ni;
             wxLogTrace( "PNS", "iter %d: reverse-collide-segment ", aIter );
-            LINE revLine = assembleLine( seg );
+            LINE revLine = assembleLine( (SEGMENT*) ni );
 
             popLineStack();
             st = onCollidingLine( revLine, currentLine );
@@ -982,7 +1039,9 @@ SHOVE::SHOVE_STATUS SHOVE::shoveIteration( int aIter )
         }
     }
     else
-    { // "forward" collisions
+    {
+        // Collision with a lower-ranking object or a solid
+        //
         switch( ni->Kind() )
         {
         case ITEM::SEGMENT_T:
@@ -1018,6 +1077,12 @@ SHOVE::SHOVE_STATUS SHOVE::shoveIteration( int aIter )
 }
 
 
+/*
+ * Resolve collisions.
+ * Each iteration pushes the next colliding object out of the way.  Iterations are continued as
+ * long as they propagate further collisions, or until the iteration timeout or max iteration
+ * count is reached.
+ */
 SHOVE::SHOVE_STATUS SHOVE::shoveMainLoop()
 {
     SHOVE_STATUS st = SH_OK;
@@ -1093,11 +1158,15 @@ SHOVE::SHOVE_STATUS SHOVE::ShoveLines( const LINE& aCurrentHead )
     m_newHead = OPT_LINE();
     m_logger.Clear();
 
+    // Pop NODEs containing previous shoves which are no longer necessary
+    //
     ITEM_SET headSet;
     headSet.Add( aCurrentHead );
 
     NODE* parent = reduceSpringback( headSet, nullptr );
 
+    // Create a new NODE to store this version of the world
+    //
     m_currentNode = parent->Branch();
     m_currentNode->ClearRanks();
     m_currentNode->Add( head );
@@ -1263,14 +1332,14 @@ SHOVE::SHOVE_STATUS SHOVE::ShoveDraggingVia( VIA* aVia, const VECTOR2I& aWhere,
     m_newHead = OPT_LINE();
     m_draggedVia = NULL;
 
+    // Pop NODEs containing previous shoves which are no longer necessary
+    //
     ITEM_SET headSet;
     headSet.Add( *aVia );
 
-    // Pop NODEs containing previous shoves which are no longer necessary
-    //
     NODE* parent = reduceSpringback( headSet, &aVia );
 
-    // Create a new NODE
+    // Create a new NODE to store this version of the world
     //
     m_currentNode = parent->Branch();
     m_currentNode->ClearRanks();

pcbnew/router/pns_via.cpp

@@ -94,6 +94,7 @@ VIA* VIA::Clone() const
     v->m_rank = m_rank;
     v->m_marker = m_marker;
     v->m_viaType = m_viaType;
+    v->m_parent = m_parent;
 
     return v;
 }

pcbnew/router/pns_via.h

@@ -66,7 +66,7 @@ public:
 
 
     VIA( const VIA& aB ) :
-        ITEM( VIA_T )
+        ITEM( aB )
     {
         SetNet( aB.Net() );
         SetLayers( aB.Layers() );