Fix T54544: "Copy Materials to Selected" only works when materials are defined on the mesh.

Build a temp matarray storing materials from obdata and source object
(depending on slots 'allocation' of source object), and assign those to
targets.

Also remove limitation of 'using same obdata is forbidden', just never
edit obdata materials in that case...

Certainly not perfect, but already much better than existing code.

1 files changed, 17 insertions, 5 deletions

diff --git a/source/blender/editors/render/render_shading.c b/source/blender/editors/render/render_shading.c
index 149bae718a0..536252f5003 100644
--- a/source/blender/editors/render/render_shading.c
+++ b/source/blender/editors/render/render_shading.c
@@ -465,17 +465,27 @@ static int material_slot_copy_exec(bContext *C, wmOperator *UNUSED(op))
 {
   Main *bmain = CTX_data_main(C);
   Object *ob = ED_object_context(C);
-  Material ***matar;
+  Material ***matar_obdata;
 
-  if (!ob || !(matar = BKE_object_material_array_p(ob))) {
+  if (!ob || !(matar_obdata = BKE_object_material_array_p(ob))) {
     return OPERATOR_CANCELLED;
   }
 
+  BLI_assert(ob->totcol == *BKE_object_material_len_p(ob));
+
+  Material ***matar_object = &ob->mat;
+
+  Material **matar = MEM_callocN(sizeof(*matar) * (size_t)ob->totcol, __func__);
+  for (int i = ob->totcol; i--;) {
+    matar[i] = ob->matbits[i] ? (*matar_object)[i] : (*matar_obdata)[i];
+  }
+
   CTX_DATA_BEGIN (C, Object *, ob_iter, selected_editable_objects) {
     if (ob != ob_iter && BKE_object_material_array_p(ob_iter)) {
-      if (ob->data != ob_iter->data) {
-        BKE_object_material_array_assign(bmain, ob_iter, matar, ob->totcol);
-      }
+      /* If we are using the same obdata, we only assign slots in ob_iter that are using object
+       * materials, and not obdata ones. */
+      const bool is_same_obdata = ob->data == ob_iter->data;
+      BKE_object_material_array_assign(bmain, ob_iter, &matar, ob->totcol, is_same_obdata);
 
       if (ob_iter->totcol == ob->totcol) {
         ob_iter->actcol = ob->actcol;
@@ -486,6 +496,8 @@ static int material_slot_copy_exec(bContext *C, wmOperator *UNUSED(op))
   }
   CTX_DATA_END;
 
+  MEM_freeN(matar);
+
   return OPERATOR_FINISHED;
 }