Fix T44611: 'make_links_data' modifiers would fail and crash with multires modifier.

Since it was not ensuring dest has valid mdisp data matching new multires modifier subdiv level...

Also, fixed a bug in `multires_subdivide()`, which would crash when trying to
increase from level 0 (aka no subdiv) to > 1 (wrong check, trying to interpolate
when it should not). And added a few sanity checks.

1 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/object.c b/source/blender/blenkernel/intern/object.c
index bd0b7275174..5b29187e7cd 100644
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -96,6 +96,7 @@
 #include "BKE_editmesh.h"
 #include "BKE_mball.h"
 #include "BKE_modifier.h"
+#include "BKE_multires.h"
 #include "BKE_node.h"
 #include "BKE_object.h"
 #include "BKE_paint.h"
@@ -280,6 +281,12 @@ void BKE_object_link_modifiers(struct Object *ob_dst, struct Object *ob_src)
 
 		nmd = modifier_new(md->type);
 		BLI_strncpy(nmd->name, md->name, sizeof(nmd->name));
+
+		if (md->type == eModifierType_Multires) {
+			/* Has to be done after mod creation, but *before* we actually copy its settings! */
+			multiresModifier_sync_levels_ex(ob_dst, (MultiresModifierData *)md, (MultiresModifierData *)nmd);
+		}
+
 		modifier_copyData(md, nmd);
 		BLI_addtail(&ob_dst->modifiers, nmd);
 		modifier_unique_name(&ob_dst->modifiers, nmd);