From f10193490907b55019e21c5b16b77cc9c05fd877 Mon Sep 17 00:00:00 2001
From: Jon Evans <jon@craftyjon.com>
Date: Sat, 25 May 2019 15:01:54 -0400
Subject: [PATCH] Report actual intersection position for crossing tracks

Fixes: lp:1825588
* https://bugs.launchpad.net/kicad/+bug/1825588
---
 common/geometry/trigo.cpp               | 14 +++++++++-----
 include/trigo.h                         |  4 +++-
 pcbnew/drc_clearance_test_functions.cpp | 24 ++++++++++++++++++++----
 3 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/common/geometry/trigo.cpp b/common/geometry/trigo.cpp
index a20e81cd01..92e1230351 100644
--- a/common/geometry/trigo.cpp
+++ b/common/geometry/trigo.cpp
@@ -56,7 +56,8 @@ bool IsPointOnSegment( const wxPoint& aSegStart, const wxPoint& aSegEnd,
 
 // Returns true if the segment 1 intersectd the segment 2.
 bool SegmentIntersectsSegment( const wxPoint &a_p1_l1, const wxPoint &a_p2_l1,
-                               const wxPoint &a_p1_l2, const wxPoint &a_p2_l2 )
+                               const wxPoint &a_p1_l2, const wxPoint &a_p2_l2,
+                               wxPoint* aIntersectionPoint )
 {
 
     //We are forced to use 64bit ints because the internal units can oveflow 32bit ints when
@@ -87,10 +88,13 @@ bool SegmentIntersectsSegment( const wxPoint &a_p1_l1, const wxPoint &a_p2_l1,
     num_a = dY_ab * dX_b - dY_b * dX_ab;
     num_b = dY_ab * dX_a - dY_a * dX_ab;
 
-    //We wont calculate directly the u_k of the intersection point to avoid floating point
-    // division but they could be calculated with:
-    // u_a = (float) num_a / (float) den;
-    // u_b = (float) num_b / (float) den;
+    // Only compute the intersection point if requested
+    if( aIntersectionPoint )
+    {
+        *aIntersectionPoint = a_p1_l1;
+        aIntersectionPoint->x += KiROUND( dX_a * ( double )num_a / ( double )den );
+        aIntersectionPoint->y += KiROUND( dY_a * ( double )num_b / ( double )den );
+    }
 
     if( den < 0 )
     {
diff --git a/include/trigo.h b/include/trigo.h
index e3e87e6c01..386cd29b17 100644
--- a/include/trigo.h
+++ b/include/trigo.h
@@ -52,11 +52,13 @@ bool IsPointOnSegment( const wxPoint& aSegStart, const wxPoint& aSegEnd,
  * @param a_p2_l1 The second point of the first line.
  * @param a_p1_l2 The first point of the second line.
  * @param a_p2_l2 The second point of the second line.
+ * @param aIntersectionPoint is filled with the intersection point if it exists
  * @return bool - true if the two segments defined by four points intersect.
  * (i.e. if the 2 segments have at least a common point)
  */
 bool SegmentIntersectsSegment( const wxPoint &a_p1_l1, const wxPoint &a_p2_l1,
-                               const wxPoint &a_p1_l2, const wxPoint &a_p2_l2 );
+                               const wxPoint &a_p1_l2, const wxPoint &a_p2_l2,
+                               wxPoint* aIntersectionPoint = nullptr );
 
 /*
  * Calculate the new point of coord coord pX, pY,
diff --git a/pcbnew/drc_clearance_test_functions.cpp b/pcbnew/drc_clearance_test_functions.cpp
index 952d8429fd..9af021a36b 100644
--- a/pcbnew/drc_clearance_test_functions.cpp
+++ b/pcbnew/drc_clearance_test_functions.cpp
@@ -606,8 +606,10 @@ bool DRC::doTrackDrc( TRACK* aRefSeg, TRACK* aStart, bool aTestPads, bool aTestZ
 
             if( ( segStartPoint.y < 0 ) && ( segEndPoint.y > 0 ) )
             {
-                markers.push_back(
-                        m_markerFactory.NewMarker( aRefSeg, track, seg, DRCE_TRACKS_CROSSING ) );
+                MARKER_PCB* m = m_markerFactory.NewMarker( aRefSeg, track, seg,
+                                                           DRCE_TRACKS_CROSSING );
+                m->SetPosition( wxPoint( track->GetStart().x, aRefSeg->GetStart().y ) );
+                markers.push_back( m );
 
                 if( !handleNewMarker() )
                     return false;
@@ -654,8 +656,22 @@ bool DRC::doTrackDrc( TRACK* aRefSeg, TRACK* aStart, bool aTestPads, bool aTestZ
 
                 if( !checkLine( segStartPoint, segEndPoint ) )
                 {
-                    markers.push_back(
-                            m_markerFactory.NewMarker( aRefSeg, track, seg, DRCE_ENDS_PROBLEM3 ) );
+                    wxPoint failurePoint;
+                    MARKER_PCB* m;
+
+                    if( SegmentIntersectsSegment( aRefSeg->GetStart(), aRefSeg->GetEnd(),
+                                                  track->GetStart(), track->GetEnd(),
+                                                  &failurePoint ) )
+                    {
+                        m = m_markerFactory.NewMarker( aRefSeg, track, seg, DRCE_TRACKS_CROSSING );
+                        m->SetPosition( failurePoint );
+                    }
+                    else
+                    {
+                        m = m_markerFactory.NewMarker( aRefSeg, track, seg, DRCE_ENDS_PROBLEM3 );
+                    }
+
+                    markers.push_back( m );
 
                     if( !handleNewMarker() )
                         return false;