Implement C++ methods for DNA structures

This change makes it possible to add implementation of common
C++ methods for DNA structures which helps ensuring unsafe
operations like shallow copy are done explicitly.

For example, creating a shallow copy used to be:

  Object temp_object = *input_object;

In the C++ context it was seen like the temp_object is
properly decoupled from the input object, while in the
reality is it not. Now this code becomes:

  Object temp_object = blender::dna::shallow_copy(*input_object);

The copy and move constructor and assignment operators are
now explicitly disabled.

Other than a more explicit resource management this change
also solves a lot of warnings generated by the implicitly
defined copy constructors w.r.t dealing with deprecated fields.
These warnings were generated by Apple Clang when a shallow
object copy was created via implicitly defined copy constructor.

In order to enable C++ methods for DNA structures a newly added
macro `DNA_DEFINE_CXX_METHODS()` is to be used:

  tpyedef struct Object {
    DNA_DEFINE_CXX_METHODS(Object)
    ...
  } Object;

For the shallow copy use `blender::dna::shallow_copy()`.

The implementation of the memcpy is hidden via an internal DNA
function to avoid pulling `string.h` into every DNA header.
This means that the solution does not affect on the headers
dependencies.

---

Ideally `DNA_shallow_copy` would be defined in a more explicit
header, but don;t think we have a suitable one already. Maybe
we can introduce `DNA_access.h` ?

Differential Revision: https://developer.blender.org/D14427

2 files changed, 5 insertions, 3 deletions

diff --git a/source/blender/blenkernel/intern/mesh_convert.cc b/source/blender/blenkernel/intern/mesh_convert.cc
index 40c6fbcf67e..1be2d06ce61 100644
--- a/source/blender/blenkernel/intern/mesh_convert.cc
+++ b/source/blender/blenkernel/intern/mesh_convert.cc
@@ -910,7 +910,8 @@ static void curve_to_mesh_eval_ensure(Object &object)
    *
    * So we create temporary copy of the object which will use same data as the original bevel, but
    * will have no modifiers. */
-  Object bevel_object = {{nullptr}};
+  Object bevel_object;
+  memset(&bevel_object, 0, sizeof(bevel_object));
   if (curve.bevobj != nullptr) {
     memcpy(&bevel_object, curve.bevobj, sizeof(bevel_object));
     BLI_listbase_clear(&bevel_object.modifiers);
@@ -919,7 +920,8 @@ static void curve_to_mesh_eval_ensure(Object &object)
   }
 
   /* Same thing for taper. */
-  Object taper_object = {{nullptr}};
+  Object taper_object;
+  memset(&taper_object, 0, sizeof(taper_object));
   if (curve.taperobj != nullptr) {
     memcpy(&taper_object, curve.taperobj, sizeof(taper_object));
     BLI_listbase_clear(&taper_object.modifiers);
diff --git a/source/blender/blenkernel/intern/object.cc b/source/blender/blenkernel/intern/object.cc
index 1e3b5d77fa7..6d1eac5af49 100644
--- a/source/blender/blenkernel/intern/object.cc
+++ b/source/blender/blenkernel/intern/object.cc
@@ -3946,7 +3946,7 @@ bool BKE_object_minmax_dupli(Depsgraph *depsgraph,
       /* pass */
     }
     else {
-      Object temp_ob = *dob->ob;
+      Object temp_ob = blender::dna::shallow_copy(*dob->ob);
       /* Do not modify the original boundbox. */
       temp_ob.runtime.bb = nullptr;
       BKE_object_replace_data_on_shallow_copy(&temp_ob, dob->ob_data);