From 5b4319e0715220ba39530755e9d971cbf7fee47f Mon Sep 17 00:00:00 2001
From: Diederik van Lierop <mailat-signdiedenrezidotnl>
Date: Sat, 22 May 2010 22:06:35 +0200
Subject: [PATCH] Snapping: get rid of the false positives when calculating
 intersections

---
 src/object-snapper.cpp |  7 ++++++-
 src/snapped-curve.cpp  | 16 +++++++++++++++-
 src/snapped-curve.h    |  4 +++-
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/src/object-snapper.cpp b/src/object-snapper.cpp
index 5c0ea419b..bced0ac44 100644
--- a/src/object-snapper.cpp
+++ b/src/object-snapper.cpp
@@ -441,6 +441,9 @@ void Inkscape::ObjectSnapper::_snapPaths(SnappedConstraints &sc,
         }
     }
 
+    int num_path = 0;
+    int num_segm = 0;
+
     for (std::vector<Inkscape::SnapCandidatePath >::const_iterator it_p = _paths_to_snap_to->begin(); it_p != _paths_to_snap_to->end(); it_p++) {
         bool const being_edited = node_tool_active && (*it_p).currently_being_edited;
         //if true then this pathvector it_pv is currently being edited in the node tool
@@ -482,11 +485,13 @@ void Inkscape::ObjectSnapper::_snapPaths(SnappedConstraints &sc,
                 if (!being_edited || (c1 && c2)) {
                     Geom::Coord const dist = Geom::distance(sp_doc, p_doc);
                     if (dist < getSnapperTolerance()) {
-                        sc.curves.push_back(Inkscape::SnappedCurve(sp_dt, dist, getSnapperTolerance(), getSnapperAlwaysSnap(), false, curve, p.getSourceType(), p.getSourceNum(), it_p->target_type, it_p->target_bbox));
+                        sc.curves.push_back(Inkscape::SnappedCurve(sp_dt, num_path, num_segm, dist, getSnapperTolerance(), getSnapperAlwaysSnap(), false, curve, p.getSourceType(), p.getSourceNum(), it_p->target_type, it_p->target_bbox));
                     }
                 }
             }
+            num_segm++;
         } // End of: for (Geom::PathVector::iterator ....)
+        num_path++;
     }
 }
 
diff --git a/src/snapped-curve.cpp b/src/snapped-curve.cpp
index e7df3cfad..77bc8280c 100644
--- a/src/snapped-curve.cpp
+++ b/src/snapped-curve.cpp
@@ -12,8 +12,10 @@
 #include <2geom/crossing.h>
 #include <2geom/path-intersection.h>
 
-Inkscape::SnappedCurve::SnappedCurve(Geom::Point const &snapped_point, Geom::Coord const &snapped_distance, Geom::Coord const &snapped_tolerance, bool const &always_snap, bool const &fully_constrained, Geom::Curve const *curve, SnapSourceType source, long source_num, SnapTargetType target, Geom::OptRect target_bbox)
+Inkscape::SnappedCurve::SnappedCurve(Geom::Point const &snapped_point, int num_path, int num_segm, Geom::Coord const &snapped_distance, Geom::Coord const &snapped_tolerance, bool const &always_snap, bool const &fully_constrained, Geom::Curve const *curve, SnapSourceType source, long source_num, SnapTargetType target, Geom::OptRect target_bbox)
 {
+    _num_path = num_path;
+    _num_segm = num_segm;
     _distance = snapped_distance;
     _tolerance = std::max(snapped_tolerance, 1.0);
     _always_snap = always_snap;
@@ -32,6 +34,8 @@ Inkscape::SnappedCurve::SnappedCurve(Geom::Point const &snapped_point, Geom::Coo
 
 Inkscape::SnappedCurve::SnappedCurve()
 {
+    _num_path = 0;
+    _num_segm = 0;
     _distance = NR_HUGE;
     _tolerance = 1;
     _always_snap = false;
@@ -68,6 +72,16 @@ Inkscape::SnappedPoint Inkscape::SnappedCurve::intersect(SnappedCurve const &cur
         for (Geom::Crossings::const_iterator i = cs.begin(); i != cs.end(); i++) {
             Geom::Point p_ix = this->_curve->pointAt((*i).ta);
             Geom::Coord dist = Geom::distance(p_ix, p);
+
+            // Test if we have two segments (curves) from the same path..
+            if (this->_num_path == curve._num_path) {
+                // Never try to intersect a segment with itself
+                if (this->_num_segm == curve._num_segm) continue;
+                // Two subsequent segments (curves) in a path will have a common node; this node is not considered to be an intersection
+                if (this->_num_segm == curve._num_segm + 1 && (*i).ta == 0 && (*i).tb == 1) continue;
+                if (this->_num_segm + 1 == curve._num_segm && (*i).ta == 1 && (*i).tb == 0) continue;
+            }
+
             if (dist < best_dist) {
                 best_dist = dist;
                 best_p = p_ix;
diff --git a/src/snapped-curve.h b/src/snapped-curve.h
index 21124c678..595f84411 100644
--- a/src/snapped-curve.h
+++ b/src/snapped-curve.h
@@ -24,12 +24,14 @@ class SnappedCurve : public SnappedPoint
 {
 public:
     SnappedCurve();
-    SnappedCurve(Geom::Point const &snapped_point, Geom::Coord const &snapped_distance, Geom::Coord const &snapped_tolerance, bool const &always_snap, bool const &fully_constrained, Geom::Curve const *curve, SnapSourceType source, long source_num, SnapTargetType target, Geom::OptRect target_bbox);
+    SnappedCurve(Geom::Point const &snapped_point, int num_path, int num_segm, Geom::Coord const &snapped_distance, Geom::Coord const &snapped_tolerance, bool const &always_snap, bool const &fully_constrained, Geom::Curve const *curve, SnapSourceType source, long source_num, SnapTargetType target, Geom::OptRect target_bbox);
     ~SnappedCurve();
     Inkscape::SnappedPoint intersect(SnappedCurve const &curve, Geom::Point const &p, Geom::Matrix dt2doc) const; //intersect with another SnappedCurve
 
 private:
     Geom::Curve const *_curve;
+    int _num_path;  // Unique id of the path to which this segment belongs too
+    int _num_segm;  // Sequence number of this segment in the path
 };
 
 }
-- 
2.30.2