Mesh - Replace plugin system with registry-based factory pattern (#1033)

Replace the legacy DISCRETPLUGIN/DISCRETALGO symbol-based plugin system
with a clean registry-based factory pattern following the design of
Graphic3d_GraphicDriverFactory.

Problem: TKMesh and TKXMesh both exported the same DISCRETALGO symbol,
causing symbol collisions when both libraries were loaded. The old plugin
system required dlopen/dlsym which was error-prone and limited.

Solution: Each meshing algorithm now registers itself as a factory with
a unique name. Multiple algorithms can coexist and be selected at runtime.

New classes:
- BRepMesh_DiscretAlgoFactory: Abstract factory base with static registry
- BRepMesh_IncrementalMeshFactory: Factory for "FastDiscret" algorithm
- XBRepMesh_Factory: Factory for "XBRepMesh" algorithm

Removed (breaking changes):
- BRepMesh_PluginMacro.hxx: DISCRETPLUGIN macro
- BRepMesh_PluginEntryType.hxx: Legacy function pointer type
- BRepMesh_FactoryError.hxx: Legacy error enum
- XBRepMesh class: Replaced by XBRepMesh_Factory
- BRepMesh_DiscretFactory::Names(), SetFunctionName(), FunctionName(), ErrorStatus()
- Draw commands: mpsetfunctionname, mpgetfunctionname, mperror

Simplified BRepMesh_DiscretFactory API to delegate to the new registry.
Updated MeshTest_PluginCommands to use BRepMesh_DiscretAlgoFactory.

Author: dpasukhi

src/Draw/TKTopTest/MeshTest/MeshTest_PluginCommands.cxx

@@ -15,9 +15,9 @@
 
 #include <BRep_Tool.hxx>
 #include <BRepGProp.hxx>
+#include <BRepMesh_DiscretAlgoFactory.hxx>
 #include <BRepMesh_DiscretFactory.hxx>
 #include <BRepMesh_DiscretRoot.hxx>
-#include <BRepMesh_FactoryError.hxx>
 #include <BRepMesh_IncrementalMesh.hxx>
 #include <DBRep.hxx>
 #include <Draw.hxx>
@@ -48,9 +48,6 @@
 static int mpnames(Draw_Interpretor&, int, const char**);
 static int mpsetdefaultname(Draw_Interpretor&, int, const char**);
 static int mpgetdefaultname(Draw_Interpretor&, int, const char**);
-static int mpsetfunctionname(Draw_Interpretor&, int, const char**);
-static int mpgetfunctionname(Draw_Interpretor&, int, const char**);
-static int mperror(Draw_Interpretor&, int, const char**);
 static int mpincmesh(Draw_Interpretor&, int, const char**);
 static int mpparallel(Draw_Interpretor&, int, const char**);
 static int triarea(Draw_Interpretor&, int, const char**);
@@ -69,13 +66,18 @@ void MeshTest::PluginCommands(Draw_Interpretor& theCommands)
   //
   const char* g = "Mesh Commands";
   // Commands
-  theCommands.Add("mpnames", "use mpnames", __FILE__, mpnames, g);
-  theCommands.Add("mpsetdefaultname", "use mpsetdefaultname", __FILE__, mpsetdefaultname, g);
-  theCommands.Add("mpgetdefaultname", "use mpgetdefaultname", __FILE__, mpgetdefaultname, g);
-  theCommands.Add("mpsetfunctionname", "use mpsetfunctionname", __FILE__, mpsetfunctionname, g);
-  theCommands.Add("mpgetfunctionname", "use mpgetfunctionname", __FILE__, mpgetfunctionname, g);
-  theCommands.Add("mperror", "use mperror", __FILE__, mperror, g);
-  theCommands.Add("mpincmesh", "use mpincmesh", __FILE__, mpincmesh, g);
+  theCommands.Add("mpnames", "mpnames : list available meshing algorithms", __FILE__, mpnames, g);
+  theCommands.Add("mpsetdefaultname",
+                  "mpsetdefaultname name : set default meshing algorithm",
+                  __FILE__,
+                  mpsetdefaultname,
+                  g);
+  theCommands.Add("mpgetdefaultname",
+                  "mpgetdefaultname : get default meshing algorithm name",
+                  __FILE__,
+                  mpgetdefaultname,
+                  g);
+  theCommands.Add("mpincmesh", "mpincmesh shape deflection [angle]", __FILE__, mpincmesh, g);
   theCommands.Add("mpparallel",
                   "mpparallel [toTurnOn] : show / set multi-threading flag for incremental mesh",
                   __FILE__,
@@ -98,176 +100,110 @@ void MeshTest::PluginCommands(Draw_Interpretor& theCommands)
 
 static int mpnames(Draw_Interpretor&, int n, const char**)
 {
-  int                                                aNb;
-  NCollection_Map<TCollection_AsciiString>::Iterator aIt;
-  //
   if (n != 1)
   {
     printf(" use mpnames\n");
     return 0;
   }
-  //
-  const NCollection_Map<TCollection_AsciiString>& aMN = BRepMesh_DiscretFactory::Get().Names();
-  aNb                                                 = aMN.Extent();
-  if (!aNb)
+
+  const NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>>& aFactories =
+    BRepMesh_DiscretAlgoFactory::Factories();
+
+  if (aFactories.IsEmpty())
   {
-    printf(" *no names found\n");
+    printf(" *no algorithms registered\n");
     return 0;
   }
-  //
-  printf(" *available names:\n");
-  aIt.Initialize(aMN);
-  for (; aIt.More(); aIt.Next())
+
+  printf(" *available algorithms:\n");
+  for (NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>>::Iterator anIter(aFactories);
+       anIter.More();
+       anIter.Next())
   {
-    const TCollection_AsciiString& aName = aIt.Key();
-    printf("  %s\n", aName.ToCString());
+    printf("  %s\n", anIter.Value()->Name().ToCString());
   }
-  //
+
   return 0;
 }
 
 //=================================================================================================
 
 static int mpsetdefaultname(Draw_Interpretor&, int n, const char** a)
 {
-  TCollection_AsciiString aName;
-  //
   if (n != 2)
   {
     printf(" use mpsetdefaultname name\n");
     return 0;
   }
-  //
-  aName = a[1];
-  //
+
+  TCollection_AsciiString aName = a[1];
   if (BRepMesh_DiscretFactory::Get().SetDefaultName(aName))
+  {
     printf(" *ready\n");
+  }
   else
-    printf(" *fault\n");
-  //
-  return 0;
-}
-
-//=================================================================================================
-
-static int mpgetdefaultname(Draw_Interpretor&, int n, const char**)
-{
-  if (n != 1)
   {
-    printf(" use mpgetdefaultname\n");
-    return 0;
+    printf(" *algorithm '%s' not found\n", aName.ToCString());
   }
-  //
-  const TCollection_AsciiString& aName = BRepMesh_DiscretFactory::Get().DefaultName();
-  printf(" *default name: %s\n", aName.ToCString());
-  //
-  return 0;
-}
-
-//=================================================================================================
 
-static int mpsetfunctionname(Draw_Interpretor&, int n, const char** a)
-{
-  TCollection_AsciiString aName;
-  //
-  if (n != 2)
-  {
-    printf(" use mpsetfunctionname name\n");
-    return 0;
-  }
-  //
-  aName = a[1];
-  //
-  if (BRepMesh_DiscretFactory::Get().SetFunctionName(aName))
-    printf(" *ready\n");
-  else
-    printf(" *fault\n");
-  //
   return 0;
 }
 
 //=================================================================================================
 
-static int mpgetfunctionname(Draw_Interpretor&, int n, const char**)
+static int mpgetdefaultname(Draw_Interpretor&, int n, const char**)
 {
   if (n != 1)
   {
-    printf(" use mpgetfunctionname\n");
+    printf(" use mpgetdefaultname\n");
     return 0;
   }
-  //
-  const TCollection_AsciiString& aName = BRepMesh_DiscretFactory::Get().FunctionName();
-  printf(" *function name: %s\n", aName.ToCString());
-  //
-  return 0;
-}
 
-//=================================================================================================
+  const TCollection_AsciiString& aName = BRepMesh_DiscretFactory::Get().DefaultName();
+  printf(" *default name: %s\n", aName.ToCString());
 
-static int mperror(Draw_Interpretor&, int n, const char**)
-{
-  BRepMesh_FactoryError aErr;
-  //
-  if (n != 1)
-  {
-    printf(" use mperror\n");
-    return 0;
-  }
-  //
-  aErr = BRepMesh_DiscretFactory::Get().ErrorStatus();
-  printf(" *ErrorStatus: %d\n", (int)aErr);
-  //
   return 0;
 }
 
 //=================================================================================================
 
 static int mpincmesh(Draw_Interpretor&, int n, const char** a)
 {
-  double       aDeflection, aAngle;
-  TopoDS_Shape aS;
-  //
   if (n < 3)
   {
-    printf(" use mpincmesh s deflection [angle]\n");
+    printf(" use mpincmesh shape deflection [angle]\n");
     return 0;
   }
-  //
-  aS = DBRep::Get(a[1]);
+
+  TopoDS_Shape aS = DBRep::Get(a[1]);
   if (aS.IsNull())
   {
-    printf(" null shapes is not allowed here\n");
+    printf(" null shape is not allowed here\n");
     return 0;
   }
-  //
-  aDeflection = Draw::Atof(a[2]);
-  aAngle      = 0.5;
+
+  double aDeflection = Draw::Atof(a[2]);
+  double aAngle      = 0.5;
   if (n > 3)
   {
     aAngle = Draw::Atof(a[3]);
   }
-  //
+
   occ::handle<BRepMesh_DiscretRoot> aMeshAlgo =
     BRepMesh_DiscretFactory::Get().Discret(aS, aDeflection, aAngle);
-  //
-  BRepMesh_FactoryError aErr = BRepMesh_DiscretFactory::Get().ErrorStatus();
-  if (aErr != BRepMesh_FE_NOERROR)
-  {
-    printf(" *Factory::Get().ErrorStatus()=%d\n", (int)aErr);
-  }
-  //
+
   if (aMeshAlgo.IsNull())
   {
-    printf(" *Can not create the algo\n");
+    printf(" *Cannot create the meshing algorithm\n");
     return 0;
   }
-  //
+
   aMeshAlgo->Perform();
   if (!aMeshAlgo->IsDone())
   {
-    printf(" *Not done\n");
+    printf(" *Meshing not done\n");
   }
-  //
+
   return 0;
 }
 

src/ModelingAlgorithms/TKMesh/BRepMesh/BRepMesh_DiscretAlgoFactory.cxx

@@ -0,0 +1,114 @@
+// Copyright (c) 2025 OPEN CASCADE SAS
+//
+// This file is part of Open CASCADE Technology software library.
+//
+// This library is free software; you can redistribute it and/or modify it under
+// the terms of the GNU Lesser General Public License version 2.1 as published
+// by the Free Software Foundation, with special exception defined in the file
+// OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
+// distribution for complete text of the license and disclaimer of any warranty.
+//
+// Alternatively, this file may be used under the terms of Open CASCADE
+// commercial license or contractual agreement.
+
+#include <BRepMesh_DiscretAlgoFactory.hxx>
+
+#include <BRepMesh_DiscretRoot.hxx>
+
+IMPLEMENT_STANDARD_RTTIEXT(BRepMesh_DiscretAlgoFactory, Standard_Transient)
+
+namespace
+{
+static NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>>& getFactories()
+{
+  static NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>> TheFactories;
+  return TheFactories;
+}
+} // namespace
+
+//==================================================================================================
+
+const NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>>& BRepMesh_DiscretAlgoFactory::
+  Factories()
+{
+  return getFactories();
+}
+
+//==================================================================================================
+
+void BRepMesh_DiscretAlgoFactory::RegisterFactory(
+  const occ::handle<BRepMesh_DiscretAlgoFactory>& theFactory,
+  bool                                            theIsPreferred)
+{
+  const TCollection_AsciiString                               aName      = theFactory->Name();
+  NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>>& aFactories = getFactories();
+  if (theIsPreferred)
+  {
+    UnregisterFactory(aName);
+    aFactories.Prepend(theFactory);
+    return;
+  }
+
+  for (NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>>::Iterator anIter(aFactories);
+       anIter.More();
+       anIter.Next())
+  {
+    if (TCollection_AsciiString::IsSameString(anIter.Value()->Name(), aName, false))
+    {
+      return;
+    }
+  }
+  aFactories.Append(theFactory);
+}
+
+//==================================================================================================
+
+void BRepMesh_DiscretAlgoFactory::UnregisterFactory(const TCollection_AsciiString& theName)
+{
+  NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>>& aFactories = getFactories();
+  for (NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>>::Iterator anIter(aFactories);
+       anIter.More();)
+  {
+    if (TCollection_AsciiString::IsSameString(anIter.Value()->Name(), theName, false))
+    {
+      aFactories.Remove(anIter);
+    }
+    else
+    {
+      anIter.Next();
+    }
+  }
+}
+
+//==================================================================================================
+
+occ::handle<BRepMesh_DiscretAlgoFactory> BRepMesh_DiscretAlgoFactory::DefaultFactory()
+{
+  const NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>>& aFactories = getFactories();
+  return !aFactories.IsEmpty() ? aFactories.First() : occ::handle<BRepMesh_DiscretAlgoFactory>();
+}
+
+//==================================================================================================
+
+occ::handle<BRepMesh_DiscretAlgoFactory> BRepMesh_DiscretAlgoFactory::FindFactory(
+  const TCollection_AsciiString& theName)
+{
+  const NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>>& aFactories = getFactories();
+  for (NCollection_List<occ::handle<BRepMesh_DiscretAlgoFactory>>::Iterator anIter(aFactories);
+       anIter.More();
+       anIter.Next())
+  {
+    if (TCollection_AsciiString::IsSameString(anIter.Value()->Name(), theName, false))
+    {
+      return anIter.Value();
+    }
+  }
+  return occ::handle<BRepMesh_DiscretAlgoFactory>();
+}
+
+//==================================================================================================
+
+BRepMesh_DiscretAlgoFactory::BRepMesh_DiscretAlgoFactory(const TCollection_AsciiString& theName)
+    : myName(theName)
+{
+}