Fix crash when making objects to share same mesh

Make it more reliable and predictable way of getting pointer to
an original mesh which came from copy-on-write engine.

Related change: made it (hopefully) more clear name for flags.

3 files changed, 9 insertions, 11 deletions

diff --git a/source/blender/blenkernel/intern/DerivedMesh.c b/source/blender/blenkernel/intern/DerivedMesh.c
index c554d5e7b6c..1698946b506 100644
--- a/source/blender/blenkernel/intern/DerivedMesh.c
+++ b/source/blender/blenkernel/intern/DerivedMesh.c
@@ -2790,7 +2790,7 @@ static void editbmesh_calc_modifiers(
 			}
 			else {
 				struct Mesh *mesh = ob->data;
-				if (mesh->id.tag & LIB_TAG_COPY_ON_WRITE) {
+				if (mesh->id.tag & LIB_TAG_COPIED_ON_WRITE) {
 					BKE_mesh_runtime_ensure_edit_data(mesh);
 					mesh->runtime.edit_data->vertexCos = MEM_dupallocN(deformedVerts);
 				}
@@ -2832,7 +2832,7 @@ static void editbmesh_calc_modifiers(
 	else {
 		/* this is just a copy of the editmesh, no need to calc normals */
 		struct Mesh *mesh = ob->data;
-		if (mesh->id.tag & LIB_TAG_COPY_ON_WRITE) {
+		if (mesh->id.tag & LIB_TAG_COPIED_ON_WRITE) {
 			BKE_mesh_runtime_ensure_edit_data(mesh);
 			if (mesh->runtime.edit_data->vertexCos != NULL)
 				MEM_freeN((void *)mesh->runtime.edit_data->vertexCos);
@@ -2943,18 +2943,14 @@ static void mesh_finalize_eval(Object *object)
 	if (mesh_eval->mat != NULL) {
 		MEM_freeN(mesh_eval->mat);
 	}
+	/* Set flag which makes it easier to see what's going on in a debugger. */
+	mesh_eval->id.tag |= LIB_TAG_COPIED_ON_WRITE_EVAL_RESULT;
 	mesh_eval->mat = MEM_dupallocN(mesh->mat);
 	mesh_eval->totcol = mesh->totcol;
 	/* Make evaluated mesh to share same edit mesh pointer as original
 	 * and copied meshes.
 	 */
 	mesh_eval->edit_btmesh = mesh->edit_btmesh;
-	/* Special flags to help debugging and also to allow copy-on-write core
-	 * to understand that on re-evaluation this mesh is to be preserved and
-	 * to be remapped back to copied original mesh when used as object data.
-	 */
-	mesh_eval->id.tag |= LIB_TAG_COPY_ON_WRITE_EVAL;
-	mesh_eval->id.orig_id = &mesh->id;
 	/* Copy autosmooth settings from original mesh.
 	 * This is not done by BKE_mesh_new_nomain_from_template(), so need to take
 	 * extra care here.
@@ -2970,7 +2966,7 @@ static void mesh_finalize_eval(Object *object)
 
 	/* Object is sometimes not evaluated!
 	 * TODO(sergey): BAD TEMPORARY HACK FOR UNTIL WE ARE SMARTER */
-	if (object->id.tag & LIB_TAG_COPY_ON_WRITE) {
+	if (object->id.tag & LIB_TAG_COPIED_ON_WRITE) {
 		object->data = mesh_eval;
 	}
 	else {
diff --git a/source/blender/blenkernel/intern/lattice.c b/source/blender/blenkernel/intern/lattice.c
index 0fa20f00823..b5b62de57ec 100644
--- a/source/blender/blenkernel/intern/lattice.c
+++ b/source/blender/blenkernel/intern/lattice.c
@@ -1057,7 +1057,7 @@ void BKE_lattice_modifiers_calc(struct Depsgraph *depsgraph, Scene *scene, Objec
 		modifier_deformVerts_DM_deprecated(md, &mectx, NULL, vertexCos, numVerts);
 	}
 
-	if (ob->id.tag & LIB_TAG_COPY_ON_WRITE) {
+	if (ob->id.tag & LIB_TAG_COPIED_ON_WRITE) {
 		if (vertexCos) {
 			BKE_lattice_vertexcos_apply(ob, vertexCos);
 			MEM_freeN(vertexCos);
diff --git a/source/blender/blenkernel/intern/object.c b/source/blender/blenkernel/intern/object.c
index 2eb35908d63..9c42cc686ea 100644
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -344,7 +344,9 @@ void BKE_object_free_derived_caches(Object *ob)
 	if (ob->runtime.mesh_eval != NULL) {
 		Mesh *mesh_eval = ob->runtime.mesh_eval;
 		/* Restore initial pointer. */
-		ob->data = mesh_eval->id.orig_id;
+		if (ob->data == mesh_eval) {
+			ob->data = ob->runtime.mesh_orig;
+		}
 		/* Evaluated mesh points to edit mesh, but does not own it. */
 		mesh_eval->edit_btmesh = NULL;
 		BKE_mesh_free(mesh_eval);