From 952aaa458e2b98dc28170f0167fa81c6e5cacbe7 Mon Sep 17 00:00:00 2001
From: Abdullah Tahiri <abdullah.tahiri.yo@gmail.com>
Date: Sun, 31 Dec 2017 18:52:54 +0100
Subject: [PATCH] Sketcher: Fix transfer of tangency and perpendicular
 end-to-endpoint constraints

================================================================================

When transfering constraints to coincident points on deletion of geometry, a tangency/perpendicular constraint
cannot be blindly transfered as the destination edge may not be tangent/perpendicular leading to unexpected behaviour.

However, the user does expect that something that was coincident with such end-to-endpoint constraint (which implicitly includes a coincident constraint)
remains coincident after deletion. Therefore, the change of type to coincident.

This implicitly solves the problem of representation of constraints leading to a crash in coin3d.

fixes #3291
---
 src/Mod/Sketcher/App/SketchObject.cpp | 34 +++++++++++++++++++--------
 1 file changed, 24 insertions(+), 10 deletions(-)

diff --git a/src/Mod/Sketcher/App/SketchObject.cpp b/src/Mod/Sketcher/App/SketchObject.cpp
index 7e15171280..a011dbdf0a 100644
--- a/src/Mod/Sketcher/App/SketchObject.cpp
+++ b/src/Mod/Sketcher/App/SketchObject.cpp
@@ -1015,20 +1015,34 @@ int SketchObject::transferConstraints(int fromGeoId, PointPos fromPosId, int toG
         if (vals[i]->First == fromGeoId && vals[i]->FirstPos == fromPosId &&
             !(vals[i]->Second == toGeoId && vals[i]->SecondPos == toPosId) &&
             !(toGeoId < 0 && vals[i]->Second <0) ) {
-            Constraint *constNew = newVals[i]->clone();
-            constNew->First = toGeoId;
-            constNew->FirstPos = toPosId;
-            newVals[i] = constNew;
-            changed.push_back(constNew);
+	    // Nothing guarantees that a tangent can be freely transferred to another coincident point, as
+	    // the transfer destination edge most likely won't be intended to be tangent. However, if it is
+	    // an end to end point tangency, the user expects it to be substituted by a coincidence constraint.
+	    Constraint *constNew = newVals[i]->clone();
+	    constNew->First = toGeoId;
+	    constNew->FirstPos = toPosId;
+	      
+	    if(vals[i]->Type == Sketcher::Tangent || vals[i]->Type == Sketcher::Perpendicular)
+	      constNew->Type = Sketcher::Coincident;
+	    
+	    newVals[i] = constNew;
+	    changed.push_back(constNew);	      
         }
         else if (vals[i]->Second == fromGeoId && vals[i]->SecondPos == fromPosId &&
                  !(vals[i]->First == toGeoId && vals[i]->FirstPos == toPosId) &&
                  !(toGeoId < 0 && vals[i]->First< 0)) {
-            Constraint *constNew = newVals[i]->clone();
-            constNew->Second = toGeoId;
-            constNew->SecondPos = toPosId;
-            newVals[i] = constNew;
-            changed.push_back(constNew);
+
+	    Constraint *constNew = newVals[i]->clone();
+	    constNew->Second = toGeoId;
+	    constNew->SecondPos = toPosId;
+	    // Nothing guarantees that a tangent can be freely transferred to another coincident point, as
+	    // the transfer destination edge most likely won't be intended to be tangent. However, if it is
+	    // an end to end point tangency, the user expects it to be substituted by a coincidence constraint.	  
+	    if(vals[i]->Type == Sketcher::Tangent || vals[i]->Type == Sketcher::Perpendicular)  
+	      constNew->Type = Sketcher::Coincident;
+
+	    newVals[i] = constNew;
+	    changed.push_back(constNew);	      
         }
     }