From 834f48e4610c23ff3aca33de12600213e80e853c Mon Sep 17 00:00:00 2001
From: "Zheng, Lei" <realthunder.dev@gmail.com>
Date: Sun, 12 Mar 2017 10:45:27 +0800
Subject: [PATCH] Path.Area: improved section tolerance

Previously, a small offset in the same direction of section is added to
the section height to avoid tagent plane cut. Now we'll retry by adding
offset in the oppsite direction if the first attemp fails.
---
 src/Mod/Path/App/Area.cpp | 106 +++++++++++++++++++++++---------------
 1 file changed, 64 insertions(+), 42 deletions(-)

diff --git a/src/Mod/Path/App/Area.cpp b/src/Mod/Path/App/Area.cpp
index ddce83d6da..05bdfe893f 100644
--- a/src/Mod/Path/App/Area.cpp
+++ b/src/Mod/Path/App/Area.cpp
@@ -565,6 +565,7 @@ std::vector<shared_ptr<Area> > Area::makeSections(
             yMin<<','<<yMax<<"), Z("<<zMin<<','<<zMax<<')');
 
     std::vector<double> heights;
+    double tolerance = 0.0;
     if(_heights.empty()) {
         double z;
         double d = fabs(myParams.Stepdown);
@@ -593,7 +594,7 @@ std::vector<shared_ptr<Area> > Area::makeSections(
             z = zMax;
         else if(z < zMin)
             z = zMin;
-        double dz,tolerance;
+        double dz;
         if(myParams.Stepdown>0.0) {
             dz = z - zMin;
             tolerance = myParams.SectionTolerance;
@@ -660,56 +661,77 @@ std::vector<shared_ptr<Area> > Area::makeSections(
 
     std::vector<shared_ptr<Area> > sections;
     sections.reserve(heights.size());
+    tolerance *= 2.0;
+    bool can_retry = fabs(tolerance)>Precision::Confusion();
     for(double z : heights) {
-        gp_Pln pln(gp_Pnt(0,0,z),gp_Dir(0,0,1));
-        Standard_Real a,b,c,d;
-        pln.Coefficients(a,b,c,d);
-        BRepLib_MakeFace mkFace(pln,xMin,xMax,yMin,yMax);
-        const TopoDS_Shape &face = mkFace.Face();
+        bool retried = !can_retry;
+        while(true) {
+            gp_Pln pln(gp_Pnt(0,0,z),gp_Dir(0,0,1));
+            Standard_Real a,b,c,d;
+            pln.Coefficients(a,b,c,d);
+            BRepLib_MakeFace mkFace(pln,xMin,xMax,yMin,yMax);
+            const TopoDS_Shape &face = mkFace.Face();
 
-        shared_ptr<Area> area(new Area(&myParams));
-        area->setPlane(face);
-        for(const Shape &s : myShapes) {
-            BRep_Builder builder;
-            TopoDS_Compound comp;
-            builder.MakeCompound(comp);
-            for(TopExp_Explorer it(s.shape.Moved(loc), TopAbs_SOLID); it.More(); it.Next()) {
-                Part::CrossSection section(a,b,c,it.Current());
-                std::list<TopoDS_Wire> wires = section.slice(-d);
-                if(wires.empty()) {
-                    AREA_LOG("Section returns no wires");
-                    continue;
-                }
-
-                Part::FaceMakerBullseye mkFace;
-                mkFace.setPlane(pln);
-                for(const TopoDS_Wire &wire : wires)
-                    mkFace.addWire(wire);
-                try {
-                    mkFace.Build();
-                    if (mkFace.Shape().IsNull())
-                        AREA_WARN("FaceMakerBullseye return null shape on section");
-                    else {
-                        builder.Add(comp,mkFace.Shape());
+            shared_ptr<Area> area(new Area(&myParams));
+            area->setPlane(face);
+            for(auto it=myShapes.begin();it!=myShapes.end();++it) {
+                const auto &s = *it;
+                BRep_Builder builder;
+                TopoDS_Compound comp;
+                builder.MakeCompound(comp);
+                for(TopExp_Explorer xp(s.shape.Moved(loc), TopAbs_SOLID); xp.More(); xp.Next()) {
+                    Part::CrossSection section(a,b,c,xp.Current());
+                    std::list<TopoDS_Wire> wires = section.slice(-d);
+                    if(wires.empty()) {
+                        AREA_LOG("Section returns no wires");
                         continue;
                     }
-                }catch (Base::Exception &e){
-                    AREA_WARN("FaceMakerBullseye failed on section: " << e.what());
+                    Part::FaceMakerBullseye mkFace;
+                    mkFace.setPlane(pln);
+                    for(const TopoDS_Wire &wire : wires)
+                        mkFace.addWire(wire);
+                    try {
+                        mkFace.Build();
+                        if (mkFace.Shape().IsNull())
+                            AREA_WARN("FaceMakerBullseye return null shape on section");
+                        else {
+                            builder.Add(comp,mkFace.Shape());
+                            continue;
+                        }
+                    }catch (Base::Exception &e){
+                        AREA_WARN("FaceMakerBullseye failed on section: " << e.what());
+                    }
+                    for(const TopoDS_Wire &wire : wires)
+                        builder.Add(comp,wire);
                 }
-                for(const TopoDS_Wire &wire : wires)
-                    builder.Add(comp,wire);
-            }
 
-            // Make sure the compound has at least one edge
-            for(TopExp_Explorer it(comp,TopAbs_EDGE);it.More();) {
-                area->add(comp,s.op);
+                // Make sure the compound has at least one edge
+                TopExp_Explorer xp(comp,TopAbs_EDGE);
+                if(xp.More()) {
+                    area->add(comp,s.op);
+                }else if(area->myShapes.empty()){
+                    auto itNext = it;
+                    if(++itNext != myShapes.end() &&
+                        (itNext->op==OperationIntersection ||
+                         itNext->op==OperationDifference))
+                    {
+                        break;
+                    }
+                }
+            }
+            if(area->myShapes.size()){
+                sections.push_back(area);
                 break;
             }
+            if(retried) {
+                AREA_WARN("Discard empty section");
+                break;
+            }else{
+                AREA_TRACE("retry section " <<z<<"->"<<z+tolerance);
+                z += tolerance;
+                retried = true;
+            }
         }
-        if(area->myShapes.size())
-            sections.push_back(area);
-        else
-            AREA_WARN("Discard empty section");
         TIME_PRINT(t1,"makeSection " << z);
     }
     TIME_PRINT(t,"makeSection count: " << sections.size()<<", total");