Sketcher/BackEdit: Add camera sensor to VP that detects side and redraw if side changed

src/Mod/Sketcher/Gui/ViewProviderSketch.cpp

@@ -283,7 +283,8 @@ ViewProviderSketch::ViewProviderSketch()
     listener(nullptr),
     editCoinManager(nullptr),
     pObserver(std::make_unique<ViewProviderSketch::ParameterObserver>(*this)),
-    sketchHandler(nullptr)
+    sketchHandler(nullptr),
+    viewOrientationFactor(1)
 {
     PartGui::ViewProviderAttachExtension::initExtension(this);
 
@@ -312,6 +313,8 @@ ViewProviderSketch::ViewProviderSketch()
     //rubberband selection
     rubberband = std::make_unique<Gui::Rubberband>();
 
+    cameraSensor.setFunction(&ViewProviderSketch::camSensCB);
+
 }
 
 ViewProviderSketch::~ViewProviderSketch()
@@ -3112,16 +3115,43 @@ void ViewProviderSketch::setEditViewer(Gui::View3DInventorViewer* viewer, int Mo
     rubberband->setViewer(viewer);
 
     viewer->setupEditingRoot();
+
+    cameraSensor.setData(new VPCam{this, viewer->getSoRenderManager()->getCamera()});
+    cameraSensor.attach(&viewer->getSoRenderManager()->getCamera()->orientation);
 }
 
 void ViewProviderSketch::unsetEditViewer(Gui::View3DInventorViewer* viewer)
 {
+    delete static_cast<VPCam*>(cameraSensor.getData());
+    cameraSensor.detach();
+
     viewer->removeGraphicsItem(rubberband.get());
     viewer->setEditing(false);
     SoNode* root = viewer->getSceneGraph();
     static_cast<Gui::SoFCUnifiedSelection*>(root)->selectionRole.setValue(true);
 }
 
+void ViewProviderSketch::camSensCB(void *data, SoSensor *)
+{
+    VPCam *proxyVPCam = static_cast<VPCam*>(data);
+    auto vp = proxyVPCam->vp;
+    auto cam = proxyVPCam->cam;
+
+    auto rotSk = Base::Rotation(vp->getDocument()->getEditingTransform()); //sketch orientation
+    auto rotc = cam->orientation.getValue().getValue();
+    auto rotCam = Base::Rotation(rotc[0], rotc[1], rotc[2], rotc[3]); // camera orientation (needed because float to double conversion)
+
+    // Is camera in the same hemisphere as positive sketch normal ?
+    auto orientation = (rotCam.invert()*rotSk).multVec(Base::Vector3d(0,0,1));
+    auto tmpFactor = orientation.z<0?-1:1;
+
+    if (tmpFactor != vp->viewOrientationFactor) { // redraw only if viewing side changed
+        Base::Console().Log("Switching side, now %s, redrawing\n", tmpFactor < 0 ? "back" : "front");
+        vp->viewOrientationFactor = tmpFactor;
+        vp->draw();
+    }
+}
+
 int ViewProviderSketch::getPreselectPoint() const
 {
     if (isInEditMode())

src/Mod/Sketcher/Gui/ViewProviderSketch.h

@@ -42,6 +42,9 @@
 
 #include <Mod/Sketcher/App/GeoList.h>
 
+#include <Inventor/sensors/SoFieldSensor.h>
+#include <Inventor/nodes/SoCamera.h>
+
 class TopoDS_Shape;
 class TopoDS_Face;
 class SoSeparator;
@@ -388,6 +391,13 @@ private:
         bool buttonPress = false;
     };
 
+    /** @brief Private struct grouping ViewProvider and Camera node, to be used as SoFieldSensor data
+     */
+    struct VPCam {
+        ViewProviderSketch* vp;
+        SoCamera* cam;
+    };
+
 public:
     /// constructor
     ViewProviderSketch();
@@ -551,6 +561,7 @@ protected:
     void unsetEdit(int ModNum) override;
     void setEditViewer(Gui::View3DInventorViewer*, int ModNum) override;
     void unsetEditViewer(Gui::View3DInventorViewer*) override;
+    static void camSensCB(void *data, SoSensor *); // camera sensor callback
     //@}
 
     /** @name miscelanea editing functions */
@@ -763,6 +774,9 @@ private:
     std::unique_ptr<DrawSketchHandler> sketchHandler;
 
     ViewProviderParameters viewProviderParameters;
+
+    SoFieldSensor cameraSensor;
+    int viewOrientationFactor; // stores if sketch viewed from front or back
 };
 
 } // namespace PartGui