Add symmetry constraints without an explicit symmetry plane; these

use the horizontal or vertical axes of the active workplane. The
equations that we write from these are very fast (of the form u + v
= 0, or u - v = 0).

[git-p4: depot-paths = "//depot/solvespace/": change = 1720]

constraint.cpp

@@ -154,13 +154,17 @@ void Constraint::MenuConstrain(int id) {
             break;
 
         case GraphicsWindow::MNU_SYMMETRIC:
-            if(gs.points == 2 && gs.workplanes == 1 && gs.n == 3) {
+            if(gs.points == 2 &&
-                c.type = SYMMETRIC;
+                                ((gs.workplanes == 1 && gs.n == 3) ||
+                                 (gs.n == 2)))
+            {
                 c.entityA = gs.entity[0];
                 c.ptA = gs.point[0];
                 c.ptB = gs.point[1];
-            } else if(gs.lineSegments == 1 && gs.workplanes == 1 && gs.n == 2) {
+            } else if(gs.lineSegments == 1 && 
-                c.type = SYMMETRIC;
+                                ((gs.workplanes == 1 && gs.n == 2) ||
+                                 (gs.n == 1)))
+            {
                 int i = SS.GetEntity(gs.entity[0])->IsWorkplane() ? 1 : 0;
                 Entity *line = SS.GetEntity(gs.entity[i]);
                 c.entityA = gs.entity[1-i];
@@ -170,6 +174,26 @@ void Constraint::MenuConstrain(int id) {
                 Error("Bad selection for symmetric constraint.");
                 return;
             }
+            if(c.entityA.v == Entity::NO_ENTITY.v) {
+                if(c.workplane.v == Entity::FREE_IN_3D.v) {
+                    Error("Must be locked in to workplane when constraining "
+                          "symmetric without an explicit symmetry plane.");
+                    return;
+                }
+                Vector pa = SS.GetEntity(c.ptA)->PointGetNum();
+                Vector pb = SS.GetEntity(c.ptB)->PointGetNum();
+                Vector dp = pa.Minus(pb);
+                Entity *norm = SS.GetEntity(c.workplane)->Normal();;
+                Vector u = norm->NormalU(), v = norm->NormalV();
+                if(fabs(dp.Dot(u)) > fabs(dp.Dot(v))) {
+                    c.type = SYMMETRIC_HORIZ;
+                } else {
+                    c.type = SYMMETRIC_VERT;
+                }
+            } else {
+                // Symmetry with a symmetry plane specified explicitly.
+                c.type = SYMMETRIC;
+            }
             AddConstraint(&c);
             break;
 
@@ -567,6 +591,25 @@ void Constraint::Generate(IdList<Equation,hEquation> *l) {
             }
             break;
 
+        case SYMMETRIC_HORIZ:
+        case SYMMETRIC_VERT: {
+            Entity *a = SS.GetEntity(ptA);
+            Entity *b = SS.GetEntity(ptB);
+
+            Expr *au, *av, *bu, *bv;
+            a->PointGetExprsInWorkplane(workplane, &au, &av);
+            b->PointGetExprsInWorkplane(workplane, &bu, &bv);
+
+            if(type == SYMMETRIC_HORIZ) {
+                AddEq(l, av->Minus(bv), 0);
+                AddEq(l, au->Plus(bu), 0);
+            } else {
+                AddEq(l, au->Minus(bu), 0);
+                AddEq(l, av->Plus(bv), 0);
+            }
+            break;
+        }
+
         case HORIZONTAL:
         case VERTICAL: {
             hEntity ha, hb;

drawconstraint.cpp

@@ -307,10 +307,17 @@ void Constraint::DrawOrGetDistance(Vector *labelPos) {
             break;
         }
 
-        case SYMMETRIC: {
+        {
+        Vector n; 
+        case SYMMETRIC:
+            n = SS.GetEntity(entityA)->Normal()->NormalN(); goto s;
+        case SYMMETRIC_HORIZ:
+            n = SS.GetEntity(workplane)->Normal()->NormalU(); goto s;
+        case SYMMETRIC_VERT:
+            n = SS.GetEntity(workplane)->Normal()->NormalV(); goto s;
+s:
             Vector a = SS.GetEntity(ptA)->PointGetNum();
             Vector b = SS.GetEntity(ptB)->PointGetNum();
-            Vector n = SS.GetEntity(entityA)->Normal()->NormalN();
             for(int i = 0; i < 2; i++) {
                 Vector tail = (i == 0) ? a : b;
                 Vector d = (i == 0) ? b : a;

sketch.h

@@ -331,6 +331,8 @@ public:
     static const int EQUAL_LENGTH_LINES =  50;
     static const int LENGTH_RATIO       =  51;
     static const int SYMMETRIC          =  60;
+    static const int SYMMETRIC_HORIZ    =  61;
+    static const int SYMMETRIC_VERT     =  62;
     static const int AT_MIDPOINT        =  70;
     static const int HORIZONTAL         =  80;
     static const int VERTICAL           =  81;