source/blender/draw/engines/overlay/overlay_engine.cc

@@ -129,6 +129,7 @@ static void OVERLAY_engine_init(void *vedata)
   OVERLAY_outline_init(data);
   OVERLAY_wireframe_init(data);
   OVERLAY_paint_init(data);
+  OVERLAY_onion_skin_init(data);
 }
 
 static void OVERLAY_cache_init(void *vedata)
@@ -216,12 +217,10 @@ static void OVERLAY_cache_init(void *vedata)
   OVERLAY_image_cache_init(data);
   OVERLAY_metaball_cache_init(data);
   OVERLAY_motion_path_cache_init(data);
-  OVERLAY_onion_skin_init(data);
   OVERLAY_outline_cache_init(data);
   OVERLAY_particle_cache_init(data);
   OVERLAY_wireframe_cache_init(data);
   OVERLAY_volume_cache_init(data);
-  OVERLAY_onion_skin_init(data);
 }
 
 BLI_INLINE OVERLAY_DupliData *OVERLAY_duplidata_get(Object *ob, void *vedata, bool *do_init)

source/blender/editors/animation/anim_onion_skin.c

@@ -4,16 +4,24 @@
 
 #include "ED_onion_skin.h"
 #include "MEM_guardedalloc.h"
+#include "WM_api.h"
 #include "WM_types.h"
 
-static void add_exec(bContext *C, wmOperator *op)
+static int onion_skin_add_exec(bContext *C, wmOperator *op)
 {
-  Object *ob = CTX_data_active_object(C);
   ListBase selected = {NULL, NULL};
   CTX_data_selected_objects(C, &selected);
   Scene *scene = CTX_data_scene(C);
-  
+
+  LISTBASE_FOREACH (Object *, ob, &selected) {
+    /* Mesh *mesh; */
+    OnionSkinMesh *link = MEM_callocN(sizeof(OnionSkinMesh), "onion skin mesh link");
+    /* link->mesh = mesh; */
+    BLI_addtail(&scene->onion_skin_cache.meshes, link);
+  }
+
   BLI_freelistN(&selected);
+  return OPERATOR_FINISHED;
 }
 
 static void ANIM_OT_onion_skin_add(wmOperatorType *ot)
@@ -24,7 +32,7 @@ static void ANIM_OT_onion_skin_add(wmOperatorType *ot)
   ot->idname = "ANIM_OT_onion_skin_add";
 
   /* api callbacks */
-  ot->exec = add_exec;
+  ot->exec = onion_skin_add_exec;
   /* ot->cancel = WM_gesture_box_cancel; */
 
   /* ot->poll = ed_markers_poll_markers_exist; */
@@ -35,7 +43,7 @@ static void ANIM_OT_onion_skin_add(wmOperatorType *ot)
   /* properties */
 }
 
-ED_operatortypes_onion_skin(void)
+void ED_operatortypes_onion_skin(void)
 {
   WM_operatortype_append(ANIM_OT_onion_skin_add);
 }

source/blender/makesdna/DNA_scene_types.h

@@ -23,6 +23,7 @@
 #include "DNA_customdata_types.h" /* Scene's runtime custom-data masks. */
 #include "DNA_layer_types.h"
 #include "DNA_listBase.h"
+#include "DNA_mesh_types.h"
 #include "DNA_vec_types.h"
 #include "DNA_view3d_types.h"
 
@@ -1875,9 +1876,15 @@ enum {
 /** \name Scene ID-Block
  * \{ */
 
-typedef struct SceneOnionSkin {
+typedef struct OnionSkinMesh {
-  SceneOnionSkin *prev, *next;
+  struct OnionSkinMesh *prev, *next;
   Mesh *mesh;
+} OnionSkinMesh;
+
+typedef struct SceneOnionSkin {
+  float color[3];
+  float alpha;
+  ListBase meshes /* OnionSkinMesh */;
 } SceneOnionSkin;
 
 typedef struct Scene {
@@ -1999,7 +2006,7 @@ typedef struct Scene {
   struct SceneDisplay display;
   struct SceneEEVEE eevee;
   struct SceneGpencil grease_pencil_settings;
-  struct ListBase onion_skin_cache /* SceneOnionSkin */;
+  struct SceneOnionSkin onion_skin_cache;
 } Scene;
 
 /** \} */