From 268d57094119cb8f15de097b51f143d997799807 Mon Sep 17 00:00:00 2001
From: Jon Evans <jon@craftyjon.com>
Date: Wed, 14 Apr 2021 22:43:54 -0400
Subject: [PATCH] PNS: keep last valid diff pair trace as current state

This allows fixing/committing what is on screen even if the current
cursor position doesn't have a valid solution (the old behavior
would result in the current trace disappearing)
---
 pcbnew/router/pns_diff_pair_placer.cpp | 6 +++++-
 pcbnew/router/pns_diff_pair_placer.h   | 1 +
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/pcbnew/router/pns_diff_pair_placer.cpp b/pcbnew/router/pns_diff_pair_placer.cpp
index 9b75abc14e..f5e74b36c7 100644
--- a/pcbnew/router/pns_diff_pair_placer.cpp
+++ b/pcbnew/router/pns_diff_pair_placer.cpp
@@ -55,6 +55,7 @@ DIFF_PAIR_PLACER::DIFF_PAIR_PLACER( ROUTER* aRouter ) :
     m_snapOnTarget = false;
     m_currentEndItem = NULL;
     m_currentMode = RM_MarkObstacles;
+    m_currentTraceOk = false;
     m_idle = true;
 }
 
@@ -556,6 +557,8 @@ bool DIFF_PAIR_PLACER::Start( const VECTOR2I& aP, ITEM* aStartItem )
     m_currentEnd = p;
     m_placingVia = false;
     m_chainedPlacement = false;
+    m_currentTraceOk = false;
+    m_currentTrace = DIFF_PAIR();
 
     initPlacement();
 
@@ -655,6 +658,7 @@ bool DIFF_PAIR_PLACER::routeHead( const VECTOR2I& aP )
 
     if( result )
     {
+        m_currentTraceOk = true;
         m_currentTrace.SetNets( m_netP, m_netN );
         m_currentTrace.SetWidth( m_sizes.DiffPairWidth() );
         m_currentTrace.SetGap( m_sizes.DiffPairGap() );
@@ -668,7 +672,7 @@ bool DIFF_PAIR_PLACER::routeHead( const VECTOR2I& aP )
         return true;
     }
 
-    return false;
+    return m_currentTraceOk;
 }
 
 
diff --git a/pcbnew/router/pns_diff_pair_placer.h b/pcbnew/router/pns_diff_pair_placer.h
index 57a2660604..458317a1cc 100644
--- a/pcbnew/router/pns_diff_pair_placer.h
+++ b/pcbnew/router/pns_diff_pair_placer.h
@@ -265,6 +265,7 @@ private:
 
     VECTOR2I m_currentEnd, m_currentStart;
     DIFF_PAIR m_currentTrace;
+    bool m_currentTraceOk;
 
     ITEM* m_currentEndItem;
     PNS_MODE m_currentMode;