Only export sharp edges of the triangle mesh.

Before this commit, "emphasized edges" were displayed as well as
exported. An "emphasized edge" is an edge between triangles that
come from different faces. They are helpful in the rendered
display because they hint at the locations of faces, but not
in the 2d export since they just clutter the drawing.

After this commit, "emphasized edges" are displayed but "sharp
edges" are exported. A "sharp edge" is an edge between triangles
where the two matching vertexes have different normals, indicating
a discontiguity in the surface. "Sharp edges" are also displayed
while post-viewing the exported geometry.

src/groupmesh.cpp

@@ -403,8 +403,17 @@ void Group::GenerateDisplayItems(void) {
             displayEdges.Clear();
 
             if(SS.GW.showEdges) {
+                if(runningMesh.l.n > 0) {
+                    // Triangle mesh only; no shell or emphasized edges.
+                    runningMesh.MakeCertainEdgesInto(&displayEdges, SKdNode::EMPHASIZED_EDGES);
+                } else {
+                    if(SS.exportMode) {
+                        displayMesh.MakeCertainEdgesInto(&displayEdges, SKdNode::SHARP_EDGES);
+                    } else {
                         runningShell.MakeEdgesInto(&displayEdges);
-                runningMesh.MakeEmphasizedEdgesInto(&displayEdges);
+                        displayMesh.MakeCertainEdgesInto(&displayEdges, SKdNode::EMPHASIZED_EDGES);
+                    }
+                }
             }
         }
 

src/mesh.cpp

@@ -89,10 +89,9 @@ void SMesh::MakeEdgesInPlaneInto(SEdgeList *sel, Vector n, double d) {
     m.Clear();
 }
 
-void SMesh::MakeEmphasizedEdgesInto(SEdgeList *sel) {
+void SMesh::MakeCertainEdgesInto(SEdgeList *sel, int type) {
     SKdNode *root = SKdNode::From(this);
-    root->MakeCertainEdgesInto(sel, SKdNode::EMPHASIZED_EDGES,
+    root->MakeCertainEdgesInto(sel, type, false, NULL, NULL);
-                                false, NULL, NULL);
 }
 
 //-----------------------------------------------------------------------------
@@ -828,8 +827,11 @@ void SKdNode::FindEdgeOn(Vector a, Vector b, int cnt, bool coplanarIsInter,
             } else {
                 info->frontFacing = false;
             }
-            // And record the triangle's face
+            // Record the triangle
-            info->face = tr->meta.face;
+            info->tr = tr;
+            // And record which vertexes a and b correspond to
+            info->ai = a.Equals(tr->a) ? 0 : (a.Equals(tr->b) ? 1 : 2);
+            info->bi = b.Equals(tr->a) ? 0 : (b.Equals(tr->b) ? 1 : 2);
         } else if(((a.Equals(tr->a) && b.Equals(tr->b)) ||
                    (a.Equals(tr->b) && b.Equals(tr->c)) ||
                    (a.Equals(tr->c) && b.Equals(tr->a))))
@@ -946,7 +948,7 @@ void SKdNode::MakeCertainEdgesInto(SEdgeList *sel, int how,
                     break;
 
                 case EMPHASIZED_EDGES:
-                    if(tr->meta.face != info.face && info.count == 1) {
+                    if(tr->meta.face != info.tr->meta.face && info.count == 1) {
                         // The two triangles that join at this edge come from
                         // different faces; either really different faces,
                         // or one is from a face and the other is zero (i.e.,
@@ -955,6 +957,29 @@ void SKdNode::MakeCertainEdgesInto(SEdgeList *sel, int how,
                     }
                     break;
 
+                case SHARP_EDGES:
+                    if(info.count == 1) {
+                        Vector na0 = (j == 0) ? tr->an :
+                                    ((j == 1) ? tr->bn : tr->cn);
+                        Vector nb0 = (j == 0) ? tr->bn :
+                                    ((j == 1) ? tr->cn : tr->an);
+                        Vector na1 = (info.ai == 0) ? info.tr->an :
+                                    ((info.ai == 1) ? info.tr->bn : info.tr->cn);
+                        Vector nb1 = (info.bi == 0) ? info.tr->an :
+                                    ((info.bi == 1) ? info.tr->bn : info.tr->cn);
+                        na0 = na0.WithMagnitude(1.0);
+                        nb0 = nb0.WithMagnitude(1.0);
+                        na1 = na1.WithMagnitude(1.0);
+                        nb1 = nb1.WithMagnitude(1.0);
+                        if(!((na0.Equals(na1) && nb0.Equals(nb1)) ||
+                             (na0.Equals(nb1) && nb0.Equals(na1)))) {
+                            // The two triangles that join at this edge meet at a sharp
+                            // angle. This implies they come from different faces.
+                            sel->AddEdge(a, b);
+                        }
+                    }
+                    break;
+
                 default: oops();
             }
 

src/polygon.h

@@ -249,7 +249,7 @@ public:
     void MakeFromAssemblyOf(SMesh *a, SMesh *b);
 
     void MakeEdgesInPlaneInto(SEdgeList *sel, Vector n, double d);
-    void MakeEmphasizedEdgesInto(SEdgeList *sel);
+    void MakeCertainEdgesInto(SEdgeList *sel, int type);
 
     bool IsEmpty(void);
     void RemapFaces(Group *g, int remap);
@@ -273,7 +273,9 @@ public:
         int        count;
         bool       frontFacing;
         bool       intersectsMesh;
-        uint32_t   face;
+        STriangle *tr;
+        int        ai;
+        int        bi;
     };
 
     int which;  // whether c is x, y, or z
@@ -297,7 +299,8 @@ public:
         NAKED_OR_SELF_INTER_EDGES  = 100,
         SELF_INTER_EDGES           = 200,
         TURNING_EDGES              = 300,
-        EMPHASIZED_EDGES           = 400
+        EMPHASIZED_EDGES           = 400,
+        SHARP_EDGES                = 500,
     };
     void MakeCertainEdgesInto(SEdgeList *sel, int how, bool coplanarIsInter,
                                                 bool *inter, bool *leaky);