source/blender/blenkernel/intern/grease_pencil.cc

@@ -7,6 +7,7 @@
 #include "BKE_anim_data.h"
 #include "BKE_curves.hh"
 #include "BKE_customdata.h"
+#include "BKE_grease_pencil.h"
 #include "BKE_grease_pencil.hh"
 #include "BKE_idtype.h"
 #include "BKE_lib_id.h"
@@ -52,6 +53,10 @@ static void grease_pencil_copy_data(Main * /*bmain*/,
   GreasePencil *grease_pencil_dst = (GreasePencil *)id_dst;
   const GreasePencil *grease_pencil_src = (GreasePencil *)id_src;
 
+  /* Duplicate material array. */
+  grease_pencil_dst->material_array = static_cast<Material **>(
+      MEM_dupallocN(grease_pencil_src->material_array));
+
   /* Duplicate drawing array. */
   grease_pencil_dst->drawing_array_size = grease_pencil_src->drawing_array_size;
   grease_pencil_dst->drawing_array = MEM_cnew_array<GreasePencilDrawingOrReference *>(

source/blender/blenkernel/intern/material.cc

@@ -384,7 +384,7 @@ short *BKE_object_material_len_p(Object *ob)
   }
   if (ob->type == OB_GREASE_PENCIL) {
     GreasePencil *grease_pencil = static_cast<GreasePencil *>(ob->data);
-    return reinterpret_cast<short *>(&(grease_pencil->material_array_size));
+    return &(grease_pencil->material_array_size);
   }
   return nullptr;
 }
@@ -409,6 +409,8 @@ Material ***BKE_id_material_array_p(ID *id)
       return &(((PointCloud *)id)->mat);
     case ID_VO:
       return &(((Volume *)id)->mat);
+    case ID_GP:
+      return &(((GreasePencil *)id)->material_array);
     default:
       break;
   }
@@ -435,6 +437,8 @@ short *BKE_id_material_len_p(ID *id)
       return &(((PointCloud *)id)->totcol);
     case ID_VO:
       return &(((Volume *)id)->totcol);
+    case ID_GP:
+      return &(((GreasePencil *)id)->material_array_size);
     default:
       break;
   }

source/blender/editors/object/object_add.cc

@@ -3087,6 +3087,8 @@ static int object_convert_exec(bContext *C, wmOperator *op)
 
       bke::gpencil::convert::legacy_gpencil_to_grease_pencil(*new_grease_pencil, *gpd);
 
+      BKE_id_materials_copy(bmain, &gpd->id, &new_grease_pencil->id);
+
       BKE_object_free_derived_caches(newob);
       BKE_object_free_modifiers(newob, 0);
     }

source/blender/makesdna/DNA_grease_pencil_types.h

@@ -181,7 +181,8 @@ typedef struct GreasePencil {
    * An array of materials.
    */
   struct Material **material_array;
-  int material_array_size;
+  short material_array_size;
+  char _pad2[2];
 
   /**
    * Global flag on the data-block.