4 files changed, 60 insertions, 4 deletions

diff --git a/source/blender/blenkernel/BKE_object.h b/source/blender/blenkernel/BKE_object.h
index 17d90e64459..4d699e1ff54 100644
--- a/source/blender/blenkernel/BKE_object.h
+++ b/source/blender/blenkernel/BKE_object.h
@@ -163,9 +163,12 @@ int BKE_object_visibility(const struct Object *ob, int dag_eval_mode);
 
 /**
  * More general add: creates minimum required data, but without vertices etc.
+ *
+ * \param bmain: The main to add the object to. May be null for #LIB_ID_CREATE_NO_MAIN behavior.
  */
-struct Object *BKE_object_add_only_object(struct Main *bmain, int type, const char *name)
-    ATTR_NONNULL(1) ATTR_RETURNS_NONNULL;
+struct Object *BKE_object_add_only_object(struct Main *bmain,
+                                          int type,
+                                          const char *name) ATTR_RETURNS_NONNULL;
 /**
  * General add: to scene, with layer from area and default name.
  *
diff --git a/source/blender/blenkernel/intern/icons.cc b/source/blender/blenkernel/intern/icons.cc
index 8883613786b..2ba6510ee71 100644
--- a/source/blender/blenkernel/intern/icons.cc
+++ b/source/blender/blenkernel/intern/icons.cc
@@ -416,7 +416,7 @@ void BKE_previewimg_id_custom_set(ID *id, const char *path)
 
 bool BKE_previewimg_id_supports_jobs(const ID *id)
 {
-  return ELEM(GS(id->name), ID_OB, ID_MA, ID_TE, ID_LA, ID_WO, ID_IM, ID_BR);
+  return ELEM(GS(id->name), ID_OB, ID_MA, ID_TE, ID_LA, ID_WO, ID_IM, ID_BR, ID_GR);
 }
 
 void BKE_previewimg_deferred_release(PreviewImage *prv)
diff --git a/source/blender/blenkernel/intern/object.cc b/source/blender/blenkernel/intern/object.cc
index 6006ce88896..84d9002f4d2 100644
--- a/source/blender/blenkernel/intern/object.cc
+++ b/source/blender/blenkernel/intern/object.cc
@@ -2217,7 +2217,7 @@ Object *BKE_object_add_only_object(Main *bmain, int type, const char *name)
   }
 
   /* We cannot use #BKE_id_new here as we need some custom initialization code. */
-  Object *ob = (Object *)BKE_libblock_alloc(bmain, ID_OB, name, 0);
+  Object *ob = (Object *)BKE_libblock_alloc(bmain, ID_OB, name, bmain ? 0 : LIB_ID_CREATE_NO_MAIN);
 
   /* We increase object user count when linking to Collections. */
   id_us_min(&ob->id);
diff --git a/source/blender/editors/render/render_preview.cc b/source/blender/editors/render/render_preview.cc
index ef0f0b6225c..7e01754bb3a 100644
--- a/source/blender/editors/render/render_preview.cc
+++ b/source/blender/editors/render/render_preview.cc
@@ -374,6 +374,14 @@ static ID *duplicate_ids(ID *id, const bool allow_failure)
                                        LIB_ID_COPY_NO_ANIMDATA);
       return id_copy;
     }
+    case ID_GR: {
+      /* Doesn't really duplicate the collection. Just creates a collection instance empty. */
+      BLI_assert(BKE_previewimg_id_supports_jobs(id));
+      Object *instance_empty = BKE_object_add_only_object(nullptr, OB_EMPTY, nullptr);
+      instance_empty->instance_collection = (Collection *)id;
+      instance_empty->transflag |= OB_DUPLICOLLECTION;
+      return &instance_empty->id;
+    }
     /* These support threading, but don't need duplicating. */
     case ID_IM:
     case ID_BR:
@@ -884,6 +892,42 @@ static void object_preview_render(IconPreview *preview, IconPreviewSize *preview
 /** \} */
 
 /* -------------------------------------------------------------------- */
+/** \name Collection Preview
+ *
+ * For the most part this reuses the object preview code by creating an instance collection empty
+ * object and rendering that.
+ *
+ * \{ */
+
+/**
+ * Check if the collection contains any geometry that can be rendered. Otherwise there's nothing to
+ * display in the preview, so don't generate one.
+ * Objects and sub-collections hidden in the render will be skipped.
+ */
+static bool collection_preview_contains_geometry_recursive(const Collection *collection)
+{
+  LISTBASE_FOREACH (CollectionObject *, col_ob, &collection->gobject) {
+    if (col_ob->ob->visibility_flag & OB_HIDE_RENDER) {
+      continue;
+    }
+    if (OB_TYPE_IS_GEOMETRY(col_ob->ob->type)) {
+      return true;
+    }
+  }
+
+  LISTBASE_FOREACH (CollectionChild *, child_col, &collection->children) {
+    if (child_col->collection->flag & COLLECTION_HIDE_RENDER) {
+      continue;
+    }
+    if (collection_preview_contains_geometry_recursive(child_col->collection)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+/* -------------------------------------------------------------------- */
 /** \name Action Preview
  * \{ */
 
@@ -1577,6 +1621,12 @@ static void icon_preview_startjob_all_sizes(void *customdata,
             continue;
           }
           break;
+        case ID_GR:
+          BLI_assert(collection_preview_contains_geometry_recursive((Collection *)ip->id));
+          /* A collection instance empty was created, so this can just reuse the object preview
+           * rendering. */
+          object_preview_render(ip, cur_size);
+          continue;
         case ID_AC:
           action_preview_render(ip, cur_size);
           continue;
@@ -1868,6 +1918,9 @@ bool ED_preview_id_is_supported(const ID *id)
   if (GS(id->name) == ID_OB) {
     return object_preview_is_type_supported((const Object *)id);
   }
+  if (GS(id->name) == ID_GR) {
+    return collection_preview_contains_geometry_recursive((const Collection *)id);
+  }
   return BKE_previewimg_id_get_p(id) != nullptr;
 }