Use Face or 3D direction for View and ProjGroup

- use current 3D window direction as starting
  direction for DrawViewPart and ProjectionGroup
- if a Face is selected, use Face normal as
  starting direction.

src/Mod/TechDraw/Gui/DrawGuiUtil.cpp

@@ -36,6 +36,14 @@
 
 #endif
 
+#include <gp_Vec.hxx>
+#include <gp_Pnt.hxx>
+#include <gp_Trsf.hxx>
+#include <gp_Dir.hxx>
+#include <gp_Ax2.hxx>
+#include <BRepAdaptor_Surface.hxx>
+#include <BRepLProp_SLProps.hxx>
+
 #include <App/Application.h>
 #include <App/Document.h>
 #include <App/DocumentObject.h>
@@ -51,6 +59,11 @@
 #include <Gui/Document.h>
 #include <Gui/Selection.h>
 #include <Gui/MainWindow.h>
+#include <Gui/MDIView.h>
+#include <Gui/View3DInventor.h>
+#include <Gui/View3DInventorViewer.h>
+
+#include <Inventor/SbVec3f.h>
 
 #include <Mod/Part/App/PartFeature.h>
 #include <Mod/Part/App/Part2DObject.h>
@@ -67,6 +80,7 @@
 #include "DrawGuiUtil.h"
 
 using namespace TechDrawGui;
+using namespace TechDraw;
 
 //===========================================================================
 // validate helper routines
@@ -187,3 +201,87 @@ void DrawGuiUtil::dumpPointF(const char* text, const QPointF& p)
     Base::Console().Message("DUMP - dumpPointF - %s\n",text);
     Base::Console().Message("Point: (%.3f, %.3f)\n",p.x(),p.y());
 }
+
+
+std::pair<Base::Vector3d,Base::Vector3d> DrawGuiUtil::get3DDirAndRot()
+{
+    std::pair<Base::Vector3d,Base::Vector3d> result;
+    Base::Vector3d viewDir(0.0,-1.0,0.0);                                       //default to front
+    Base::Vector3d viewUp(0.0,0.0,1.0);                                         //default to top
+    Base::Vector3d viewRight(1.0,0.0,0.0);                                      //default to right
+    std::list<Gui::MDIView*> mdis = Gui::Application::Instance->activeDocument()->getMDIViews();
+    Gui::View3DInventor *view;
+    Gui::View3DInventorViewer *viewer = nullptr;
+    for (auto& m: mdis) {                                                       //find the 3D viewer
+        view = dynamic_cast<Gui::View3DInventor*>(m);
+        if (view) {
+            viewer = view->getViewer();
+            break;
+        }
+    }
+    if (!viewer) {
+        Base::Console().Log("LOG - DrawGuiUtil could not find a 3D viewer\n");
+        return std::make_pair( viewDir, viewRight);
+    }
+
+    SbVec3f dvec  = viewer->getViewDirection();
+    SbVec3f upvec = viewer->getUpDirection();
+
+    viewDir = Base::Vector3d(dvec[0], dvec[1], dvec[2]);
+    viewUp  = Base::Vector3d(upvec[0],upvec[1],upvec[2]);
+    Base::Vector3d dirXup = viewDir.Cross(viewUp);          //dir X up should give local Right
+
+    viewDir = viewDir * (-1.0);     // Inventor dir is opposite TD projection dir
+
+    result = std::make_pair(viewDir,dirXup);
+    return result;
+}
+
+std::pair<Base::Vector3d,Base::Vector3d> DrawGuiUtil::getProjDirFromFace(Part::Feature* obj, std::string faceName)
+{
+    std::pair<Base::Vector3d,Base::Vector3d> d3Dirs = get3DDirAndRot();
+    Base::Vector3d d3Up = (d3Dirs.first).Cross(d3Dirs.second);
+    std::pair<Base::Vector3d,Base::Vector3d> dirs;
+    dirs.first = Base::Vector3d(0.0,0.0,1.0);                 //set a default
+    dirs.second = Base::Vector3d(1.0,0.0,0.0);
+    Base::Vector3d projDir, rotVec;
+    projDir = d3Dirs.first;
+    rotVec = d3Dirs.second;
+
+    if (DrawUtil::getGeomTypeFromName(faceName) != "Face") {
+        Base::Console().Warning("getProjDirFromFace(%s) is not a Face\n",faceName.c_str());
+        return dirs;
+    }
+    Part::TopoShape ts = obj->Shape.getShape();
+    ts.setPlacement(obj->globalPlacement());
+    TopoDS_Shape subShape = ts.getSubShape(faceName.c_str());
+
+    const TopoDS_Face& face = TopoDS::Face(subShape);
+    TopAbs_Orientation orient = face.Orientation();
+    BRepAdaptor_Surface adapt(face);
+    
+    double u1 = adapt.FirstUParameter();
+    double u2 = adapt.LastUParameter();
+    double v1 = adapt.FirstVParameter();
+    double v2 = adapt.LastVParameter();
+    double uMid = (u1+u2)/2.0;
+    double vMid = (v1+v2)/2.0;
+
+    BRepLProp_SLProps props(adapt,uMid,vMid,2,Precision::Confusion());
+    if (props.IsNormalDefined()) {
+        gp_Dir vec = props.Normal();
+        projDir = Base::Vector3d(vec.X(),vec.Y(),vec.Z());
+        rotVec = projDir.Cross(d3Up);
+        if (orient != TopAbs_FORWARD) {
+            projDir = projDir * (-1.0);
+        }
+    }
+    else {
+        Base::Console().Log("Selected Face has no normal at midpoint\n");
+    }
+
+    dirs = std::make_pair(projDir,rotVec);
+    return dirs;
+}
+
+