From be294dabce4c6aa8241a67574c7d14091ec5a42a Mon Sep 17 00:00:00 2001
From: Jon Evans <jon@craftyjon.com>
Date: Mon, 28 Dec 2020 16:36:42 -0500
Subject: [PATCH] PNS: Snap back to last valid point when committing a drag

Fixes https://gitlab.com/kicad/code/kicad/-/issues/6651
---
 pcbnew/router/pns_dragger.cpp | 62 +++++++++++++++++++++--------------
 pcbnew/router/pns_dragger.h   |  1 +
 2 files changed, 38 insertions(+), 25 deletions(-)

diff --git a/pcbnew/router/pns_dragger.cpp b/pcbnew/router/pns_dragger.cpp
index 417063f6fe..b77a18227a 100644
--- a/pcbnew/router/pns_dragger.cpp
+++ b/pcbnew/router/pns_dragger.cpp
@@ -151,6 +151,7 @@ bool DRAGGER::Start( const VECTOR2I& aP, ITEM_SET& aPrimitives )
     m_draggedItems.Clear();
     m_currentMode = Settings().Mode();
     m_freeAngleMode = (m_mode & DM_FREE_ANGLE);
+    m_lastValidPoint = aP;
 
     if( m_currentMode == RM_Shove  && !m_freeAngleMode )
     {
@@ -535,19 +536,16 @@ bool DRAGGER::FixRoute()
         // invalid).  In other modes, we can only commit if "Allow DRC violations" is enabled.
         if( !m_dragStatus )
         {
-            switch( m_currentMode )
-            {
-            case RM_Shove:
-            case RM_Smart:
-                break;
+            Drag( m_lastValidPoint );
+            node = CurrentNode();
 
-            case RM_Walkaround:
-            default:
-                if( !Settings().CanViolateDRC() )
-                    return false;
-            }
+            if( !node )
+                return false;
         }
 
+        if( !m_dragStatus && !Settings().CanViolateDRC()  )
+            return false;
+
         Router()->CommitRouting( node );
         return true;
     }
@@ -558,24 +556,38 @@ bool DRAGGER::FixRoute()
 
 bool DRAGGER::Drag( const VECTOR2I& aP )
 {
+    bool ret = false;
+
     if( m_freeAngleMode )
-        return dragMarkObstacles( aP );
-
-    switch( m_currentMode )
     {
-    case RM_MarkObstacles:
-        return dragMarkObstacles( aP );
-
-    case RM_Shove:
-    case RM_Smart:
-        return dragShove( aP );
-
-    case RM_Walkaround:
-        return dragWalkaround( aP );
-
-    default:
-        return false;
+        ret = dragMarkObstacles( aP );
     }
+    else
+    {
+        switch( m_currentMode )
+        {
+        case RM_MarkObstacles:
+            ret = dragMarkObstacles( aP );
+            break;
+
+        case RM_Shove:
+        case RM_Smart:
+            ret = dragShove( aP );
+            break;
+
+        case RM_Walkaround:
+            ret = dragWalkaround( aP );
+            break;
+
+        default:
+            break;
+        }
+    }
+
+    if( ret )
+        m_lastValidPoint = aP;
+
+    return ret;
 }
 
 
diff --git a/pcbnew/router/pns_dragger.h b/pcbnew/router/pns_dragger.h
index 8dc33a4de5..170253d285 100644
--- a/pcbnew/router/pns_dragger.h
+++ b/pcbnew/router/pns_dragger.h
@@ -137,6 +137,7 @@ private:
     int                    m_draggedSegmentIndex;
     bool                   m_dragStatus;
     PNS_MODE               m_currentMode;
+    VECTOR2D               m_lastValidPoint;
 
     ///< Contains the list of items that are currently modified by the dragger
     ITEM_SET               m_draggedItems;