constraint: impove sketch plane handling

Sketch plane is now implicitly added to any constraints that accepts an
optional workplane, i.e. those supports 2D constraint

constraint.py

@@ -253,7 +253,7 @@ def _c(solver,partInfo,subname,shape,requireArc=False,retAll=False):
 
     if utils.isDraftCircle(partInfo.Part):
         part = partInfo.Part
-        w,p,n = partInfo.Workplane
+        w,p,n,_ = partInfo.Workplane
 
         if system.sketchPlane and not solver.isFixedElement(part,subname):
             system.NameTag = nameTag + '.o'
@@ -596,6 +596,15 @@ class Base(object):
             info = o.Proxy.getInfo()
             partInfo = solver.getPartInfo(info)
             ret.append(e(solver,partInfo,info.Subname,info.Shape,retAll=retAll))
+
+        if cls._workplane and len(elements)==len(cls._entityDef):
+            if solver.system.sketchPlane:
+                ret.append(solver.system.sketchPlane[0])
+            elif int(cls._workplane)>1:
+                raise RuntimeError('Constraint "{}" requires a sketch plane '
+                    'or a {} element to define a projection plane'.format(
+                    cstrName(obj), _ordinal[len(elements)]))
+
         solver.system.log('{} entities: {}'.format(cstrName(obj),ret))
         return ret
 
@@ -1030,66 +1039,57 @@ class Symmetric(Base2):
     _tooltip='Add a "{}" constraint to make two points symmetric about a plane.'
 
 
-class UseSketchPlane(Base2):
+class SymmetricHorizontal(Base2):
-    _id = -1
-    _workplane = True
-
-    @classmethod
-    def getEntities(cls,obj,solver,retAll=False):
-        ret = super(UseSketchPlane,cls).getEntities(obj,solver,retAll)
-        elements = obj.Proxy.getElements()
-        if len(elements)==len(cls._entityDef):
-            if not solver.system.sketchPlane:
-                raise RuntimeError('Constraint "{}" requires a sketch plane '
-                    'or a {} element to define a projection plane'.format(
-                    cstrName(obj), _ordinal[len(elements)]))
-            ret.append(solver.system.sketchPlane[0])
-        return ret
-
-class SymmetricHorizontal(UseSketchPlane):
     _id = 17
     _entityDef = (_p,_p)
+    _workplane = 2
 
 
-class SymmetricVertical(UseSketchPlane):
+class SymmetricVertical(Base2):
     _id = 18
     _entityDef = (_p,_p)
+    _workplane = 2
 
 
 class SymmetricLine(Base2):
     _id = 19
-    _entityDef = (_p,_p,_l,_w)
+    _entityDef = (_p,_p,_l)
+    _workplane = 2
     _iconName = 'Assembly_ConstraintSymmetricLine.svg'
     _tooltip='Add a "{}" constraint to make two points symmetric about a line.'
 
 
-class PointsHorizontal(UseSketchPlane):
+class PointsHorizontal(Base2):
     _id = 21
     _entityDef = (_p,_p)
+    _workplane = 2
     _iconName = 'Assembly_ConstraintPointsHorizontal.svg'
     _tooltip='Add a "{}" constraint to make two points horizontal with each\n'\
              'other when projected onto a plane.'
 
 
-class PointsVertical(UseSketchPlane):
+class PointsVertical(Base2):
     _id = 22
     _entityDef = (_p,_p)
+    _workplane = 2
     _iconName = 'Assembly_ConstraintPointsVertical.svg'
     _tooltip='Add a "{}" constraint to make two points vertical with each\n'\
              'other when projected onto a plane.'
 
 
-class LineHorizontal(UseSketchPlane):
+class LineHorizontal(Base2):
     _id = 23
     _entityDef = (_l,)
+    _workplane = 2
     _iconName = 'Assembly_ConstraintLineHorizontal.svg'
     _tooltip='Add a "{}" constraint to make a line segment horizontal when\n'\
              'projected onto a plane.'
 
 
-class LineVertical(UseSketchPlane):
+class LineVertical(Base2):
     _id = 24
     _entityDef = (_l,)
+    _workplane = 2
     _iconName = 'Assembly_ConstraintLineVertical.svg'
     _tooltip='Add a "{}" constraint to make a line segment vertical when\n'\
              'projected onto a plane.'

solver.py

@@ -11,9 +11,10 @@ from .system import System
 # PartName: text name of the part
 # Placement: the original placement of the part
 # Params: 7 parameters that defines the transformation of this part
-# Workplane: a tuple of three entity handles, that is the workplane, the origin
+# Workplane: a tuple of four entity handles, that is the workplane, the origin
-#            point, and the normal. The workplane, defined by the origin and
+#            point, and the normal, and x pointing normal. The workplane,
-#            norml, is essentially the XY reference plane of the part.
+#            defined by the origin and norml, is essentially the XY reference
+#            plane of the part.
 # EntityMap: string -> entity handle map, for caching
 # Group: transforming entity group handle
 PartInfo = namedtuple('SolverPartInfo', ('Part','PartName','Placement',
@@ -39,10 +40,13 @@ class Solver(object):
         # convenience constant of zero
         self.v0 = self.system.addParamV(0,group=self._fixedGroup)
 
+        # convenience normals
+        rotx = FreeCAD.Rotation(FreeCAD.Vector(0,1,0),-90)
+        self.nx = self.system.addNormal3dV(*utils.getNormal(rotx))
+
         self._fixedParts = Constraint.getFixedParts(self,cstrs)
-        if self._fixedParts is None:
+        for part in self._fixedParts:
-            self.system.log('no fixed part found')
+            self._fixedElements.add((part,None))
-            return
 
         for cstr in cstrs:
             self.system.log('preparing {}'.format(cstrName(cstr)))
@@ -181,7 +185,8 @@ class Solver(object):
         return part in self._fixedParts
 
     def isFixedElement(self,part,subname):
-        return self.isFixedPart(part) or (part,subname) in self._fixedElements
+        return (part,None) in self._fixedElements or \
+               (part,subname) in self._fixedElements
 
     def addFixedElement(self,part,subname):
         self._fixedElements.add((part,subname))
@@ -209,9 +214,12 @@ class Solver(object):
             p = self.system.addPoint3d(*params[:3],group=g)
             self.system.NameTag = info.PartName + '.n'
             n = self.system.addNormal3d(*params[3:],group=g)
+            self.system.NameTag = info.PartName + '.nx'
+            nx = self.system.addTransform(self.nx,
+                    self.v0,self.v0,self.v0,*params[3:],group=g)
             self.system.NameTag = info.PartName + '.w'
             w = self.system.addWorkplane(p,n,group=g)
-            h = (w,p,n)
+            h = (w,p,n,nx)
 
         partInfo = PartInfo(Part = info.Part,
                             PartName = info.PartName,