From 89228e1ebe86b56162d86d2c3949c621f6a7cf13 Mon Sep 17 00:00:00 2001
From: Tomasz Wlostowski <tomasz.wlostowski@cern.ch>
Date: Mon, 22 Nov 2021 01:33:32 +0100
Subject: [PATCH] router: increase parallelity detection threshold for
 AssembleDiffPair()

Partially fixes the misrecognized diff pairs issue.

Fixes: https://gitlab.com/kicad/code/kicad/-/issues/8567
---
 pcbnew/router/pns_topology.cpp | 4 ++--
 pcbnew/router/pns_topology.h   | 2 ++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/pcbnew/router/pns_topology.cpp b/pcbnew/router/pns_topology.cpp
index 32d5584c25..6f902a5403 100644
--- a/pcbnew/router/pns_topology.cpp
+++ b/pcbnew/router/pns_topology.cpp
@@ -463,7 +463,7 @@ bool TOPOLOGY::AssembleDiffPair( ITEM* aStart, DIFF_PAIR& aPair )
                     s->Width() == refSeg->Width() )
                 {
                     int dist = s->Seg().Distance( refSeg->Seg() );
-                    bool isParallel = refSeg->Seg().ApproxParallel( s->Seg() );
+                    bool isParallel = refSeg->Seg().ApproxParallel( refSeg->Seg(), DP_PARALLELITY_THRESHOLD );
                     SEG p_clip, n_clip;
 
                     bool isCoupled = commonParallelProjection( refSeg->Seg(), s->Seg(), p_clip,
@@ -496,7 +496,7 @@ bool TOPOLOGY::AssembleDiffPair( ITEM* aStart, DIFF_PAIR& aPair )
 
     int gap = -1;
 
-    if( refSeg->Seg().ApproxParallel( coupledSeg->Seg() ) )
+    if( refSeg->Seg().ApproxParallel( coupledSeg->Seg(), DP_PARALLELITY_THRESHOLD ) )
     {
         // Segments are parallel -> compute pair gap
         const VECTOR2I refDir       = refSeg->Anchor( 1 ) - refSeg->Anchor( 0 );
diff --git a/pcbnew/router/pns_topology.h b/pcbnew/router/pns_topology.h
index f02a566580..e7be18f977 100644
--- a/pcbnew/router/pns_topology.h
+++ b/pcbnew/router/pns_topology.h
@@ -88,6 +88,8 @@ public:
     const std::set<ITEM*> AssembleCluster( ITEM* aStart, int aLayer );
 
 private:
+    const int DP_PARALLELITY_THRESHOLD = 5;
+
     bool followTrivialPath( LINE* aLine, bool aLeft, ITEM_SET& aSet, std::set<ITEM*>& aVisited,
                             JOINT** aTerminalJoint = nullptr );