Fix T65741: Removing a GPencil Object's Material Slot deletes the strokes assigned to it

This was a design decision, but now we have decided to change it using the active material for the strokes using deleted material.

If the material slot is empty a new material is created to keep the strokes visible.

1 files changed, 9 insertions, 4 deletions

diff --git a/source/blender/blenkernel/intern/material.c b/source/blender/blenkernel/intern/material.c
index 1e5a2d53bfa..e845271d802 100644
--- a/source/blender/blenkernel/intern/material.c
+++ b/source/blender/blenkernel/intern/material.c
@@ -361,9 +361,6 @@ static void material_data_index_remove_id(ID *id, short index)
     case ID_MB:
       /* meta-elems don't have materials atm */
       break;
-    case ID_GD:
-      BKE_gpencil_material_index_remove((bGPdata *)id, index);
-      break;
     default:
       break;
   }
@@ -1050,12 +1047,20 @@ bool BKE_object_material_slot_remove(Main *bmain, Object *ob)
   }
 
   /* check indices from mesh */
-  if (ELEM(ob->type, OB_MESH, OB_CURVE, OB_SURF, OB_FONT, OB_GPENCIL)) {
+  if (ELEM(ob->type, OB_MESH, OB_CURVE, OB_SURF, OB_FONT)) {
     material_data_index_remove_id((ID *)ob->data, actcol - 1);
     if (ob->runtime.curve_cache) {
       BKE_displist_free(&ob->runtime.curve_cache->disp);
     }
   }
+  /* check indices from gpencil */
+  else if (ob->type == OB_GPENCIL) {
+    /* need one color */
+    if (ob->totcol == 0) {
+      BKE_gpencil_object_material_ensure_from_active_input_material(bmain, ob);
+    }
+    BKE_gpencil_material_index_reassign((bGPdata *)ob->data, ob->totcol, actcol - 1);
+  }
 
   return true;
 }