[FEM] connect CCX solver to results pipeline

- it was often criticized that our default solver CCX is not connected to the results pipeline system. One had to connect it manually, the create the different filter etc. but as soon as one changed a constraint and re-run the solver the whole work was gone and one had to recreate the pipeline.
This PR solves this by creating a pipeline and by reloading new results to it on a solver re-run.
The CCX results dialog feature is not touched, since the pipeline is hidden when the dialog is active.

src/Mod/Fem/femtaskpanels/task_result_mechanical.py

@@ -65,6 +65,11 @@ class _TaskPanel:
         # if Mesh and result are in active analysis
         # activate the result mesh object
         self.mesh_obj.ViewObject.show()
+        # hide pipeline if any
+        CCX_pipeline = FreeCADGui.ActiveDocument.getObject("SolverCCXResult")
+        if CCX_pipeline is not None:
+            self.pipeline_visibility = CCX_pipeline.Visibility
+            CCX_pipeline.hide()
 
         ui_path = FreeCAD.getHomePath() + "Mod/Fem/Resources/ui/"
         self.result_widget = FreeCADGui.PySideUic.loadUi(ui_path + "ResultShow.ui")
@@ -190,6 +195,12 @@ class _TaskPanel:
             self.result_widget.sb_displacement_factor_max.setValue(10. * scale_factor)
             self.result_widget.sb_displacement_factor.setValue(scale_factor)
 
+    def __del__(self):
+        # restore visibility
+        CCX_pipeline = FreeCADGui.ActiveDocument.getObject("SolverCCXResult")
+        if self.pipeline_visibility and CCX_pipeline is not None:
+            CCX_pipeline.Visibility = self.pipeline_visibility
+
     def restore_result_dialog(self):
         try:
             rt = FreeCAD.FEM_dialog["results_type"]

src/Mod/Fem/femtaskpanels/task_solver_ccxtools.py

@@ -74,6 +74,14 @@ class _TaskPanel:
 
         self.fem_console_message = ""
 
+        self.CCX_pipeline = None
+        self.CCX_mesh_visibility = False
+
+        # store visibility of possibly existing mesh object
+        CCX_mesh = self.fea.analysis.Document.getObject("ResultMesh")
+        if CCX_mesh is not None:
+            self.CCX_mesh_visibility = CCX_mesh.ViewObject.Visibility
+
         # Connect Signals and Slots
         QtCore.QObject.connect(
             self.form.tb_choose_working_dir,
@@ -241,6 +249,8 @@ class _TaskPanel:
         # print("calculixFinished(), exit code: {}".format(exitCode))
         FreeCAD.Console.PrintLog("calculix state: {}\n".format(self.Calculix.state()))
 
+        had_errors = False
+
         # Restore previous cwd
         QtCore.QDir.setCurrent(self.cwd)
 
@@ -250,6 +260,7 @@ class _TaskPanel:
             self.calculixNoError()
         else:
             self.calculixError()
+            had_errors = True
 
         self.form.pb_run_ccx.setText("Re-run CalculiX")
         self.femConsoleMessage("Loading result sets...")
@@ -279,10 +290,47 @@ class _TaskPanel:
             self.fea.load_results()
         except Exception:
             FreeCAD.Console.PrintError("loading results failed\n")
+            had_errors = True
 
         QApplication.restoreOverrideCursor()
         self.form.l_time.setText("Time: {0:4.1f}: ".format(time.time() - self.Start))
 
+        # create a results pipeline from the just created results object
+        if not had_errors:
+            CCX_results = self.fea.analysis.Document.getObject("CCX_Results")
+            # safe guard
+            if CCX_results is None:
+                return
+            # check if there is already a pipeline
+            self.CCX_pipeline = self.fea.analysis.Document.getObject("SolverCCXResult")
+            if self.CCX_pipeline is None:
+                try:
+                    self._createResults()
+                except Exception:
+                    FreeCAD.Console.PrintError("Results pipeline could not be created\n")
+                    had_errors = True
+            self.CCX_pipeline.load(CCX_results)
+            self.CCX_pipeline.recomputeChildren()
+            self.fea.analysis.Document.recompute()
+            # recompute() updated the result mesh data
+            # but not the shape and bar coloring
+            self.CCX_pipeline.ViewObject.updateColorBars()
+            # restore mesh object visibility
+            CCX_mesh = self.fea.analysis.Document.getObject("ResultMesh")
+            if CCX_mesh is not None:
+                CCX_mesh.ViewObject.Visibility = self.CCX_mesh_visibility
+        else:
+            FreeCAD.Console.PrintError("\nNo result pipeline was created.\n")
+
+    def _createResults(self):
+        self.CCX_pipeline = self.fea.analysis.Document.addObject(
+            "Fem::FemPostPipeline", "SolverCCXResult")
+        self.CCX_pipeline.Label = "SolverCCXResult"
+        self.CCX_pipeline.ViewObject.SelectionStyle = "BoundBox"
+        self.fea.analysis.addObject(self.CCX_pipeline)
+        # to assure the user sees something, set the default to Surface
+        self.CCX_pipeline.ViewObject.DisplayMode = "Surface"
+
     def choose_working_dir(self):
         wd = QtGui.QFileDialog.getExistingDirectory(None, "Choose CalculiX working directory",
                                                     self.fea.working_dir)