From 9898a71d030c93fe602f9ce1cbdfdbbafca0d8a3 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Wed, 3 May 2023 13:20:28 +0200
Subject: [PATCH 01/16] overlay boilerplate

---
 scripts/startup/bl_ui/space_view3d.py         |  2 +-
 source/blender/draw/CMakeLists.txt            |  3 ++
 .../draw/engines/overlay/overlay_engine.cc    |  8 +++++
 .../engines/overlay/overlay_onion_skin.cc     | 31 +++++++++++++++++++
 .../draw/engines/overlay/overlay_private.hh   |  8 +++++
 .../draw/engines/overlay/overlay_shader.cc    | 11 +++++++
 .../shaders/infos/overlay_extra_info.hh       | 17 ++++++++++
 .../shaders/overlay_onion_skin_mesh_frag.glsl |  4 +++
 .../shaders/overlay_onion_skin_mesh_vert.glsl | 11 +++++++
 9 files changed, 94 insertions(+), 1 deletion(-)
 create mode 100644 source/blender/draw/engines/overlay/overlay_onion_skin.cc
 create mode 100644 source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_frag.glsl
 create mode 100644 source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_vert.glsl

diff --git a/scripts/startup/bl_ui/space_view3d.py b/scripts/startup/bl_ui/space_view3d.py
index 81c1fe5f159..60c3ba23b86 100644
--- a/scripts/startup/bl_ui/space_view3d.py
+++ b/scripts/startup/bl_ui/space_view3d.py
@@ -6523,7 +6523,7 @@ class VIEW3D_PT_overlay_geometry(Panel):
 
         col.prop(overlay, "show_face_orientation")
 
-        # sub.prop(overlay, "show_onion_skins")
+        sub.prop(overlay, "show_onion_skins")
 
 
 class VIEW3D_PT_overlay_motion_tracking(Panel):
diff --git a/source/blender/draw/CMakeLists.txt b/source/blender/draw/CMakeLists.txt
index 3309364c074..19e97db787e 100644
--- a/source/blender/draw/CMakeLists.txt
+++ b/source/blender/draw/CMakeLists.txt
@@ -219,6 +219,7 @@ set(SRC
   engines/overlay/overlay_viewer_attribute.cc
   engines/overlay/overlay_volume.cc
   engines/overlay/overlay_wireframe.cc
+  engines/overlay/overlay_onion_skin.cc
 
   DRW_engine.h
   DRW_pbvh.hh
@@ -685,6 +686,8 @@ set(GLSL_SRC
   engines/overlay/shaders/overlay_motion_path_line_vert.glsl
   engines/overlay/shaders/overlay_motion_path_line_vert_no_geom.glsl
   engines/overlay/shaders/overlay_motion_path_point_vert.glsl
+  engines/overlay/shaders/overlay_onion_skin_mesh_frag.glsl
+  engines/overlay/shaders/overlay_onion_skin_mesh_vert.glsl
   engines/overlay/shaders/overlay_outline_detect_frag.glsl
   engines/overlay/shaders/overlay_outline_prepass_curves_vert.glsl
   engines/overlay/shaders/overlay_outline_prepass_frag.glsl
diff --git a/source/blender/draw/engines/overlay/overlay_engine.cc b/source/blender/draw/engines/overlay/overlay_engine.cc
index 0fcfc76e5ca..35aebd39b0e 100644
--- a/source/blender/draw/engines/overlay/overlay_engine.cc
+++ b/source/blender/draw/engines/overlay/overlay_engine.cc
@@ -216,10 +216,12 @@ 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)
@@ -357,6 +359,8 @@ static void OVERLAY_cache_populate(void *vedata, Object *ob)
 
   const bool draw_motion_paths = (pd->overlay.flag & V3D_OVERLAY_HIDE_MOTION_PATHS) == 0;
 
+  const bool draw_onion_skins = pd->overlay.flag & V3D_OVERLAY_ONION_SKINS;
+
   bool do_init;
   OVERLAY_DupliData *dupli = OVERLAY_duplidata_get(ob, vedata, &do_init);
 
@@ -378,6 +382,9 @@ static void OVERLAY_cache_populate(void *vedata, Object *ob)
   if (draw_bone_selection) {
     OVERLAY_pose_cache_populate(data, ob);
   }
+  if (draw_onion_skins) {
+    OVERLAY_onion_skin_populate(data, ob);
+  }
 
   if (pd->overlay.flag & V3D_OVERLAY_VIEWER_ATTRIBUTE) {
     if (is_preview) {
@@ -678,6 +685,7 @@ static void OVERLAY_draw_scene(void *vedata)
 
   OVERLAY_image_in_front_draw(data);
   OVERLAY_motion_path_draw(data);
+  OVERLAY_onion_skin_draw(data);
   OVERLAY_extra_centers_draw(data);
 
   if (DRW_state_is_select() || DRW_state_is_depth()) {
diff --git a/source/blender/draw/engines/overlay/overlay_onion_skin.cc b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
new file mode 100644
index 00000000000..7bc672b6d05
--- /dev/null
+++ b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
@@ -0,0 +1,31 @@
+#include "DRW_render.h"
+#include "overlay_private.hh"
+
+void OVERLAY_onion_skin_init(OVERLAY_Data *vedata)
+{
+  OVERLAY_PassList *psl = vedata->psl;
+  OVERLAY_PrivateData *pd = vedata->stl->pd;
+
+  DRWState state = DRW_STATE_WRITE_COLOR | DRW_STATE_BLEND_ALPHA;
+  DRW_PASS_CREATE(psl->onion_skin_ps, state | pd->clipping_state);
+
+  GPUShader *shader = OVERLAY_shader_onion_skin_mesh();
+  DRWShadingGroup *grp;
+  pd->onion_skin_grp = grp = DRW_shgroup_create(shader, psl->onion_skin_ps);
+  DRW_shgroup_uniform_block(grp, "globalsBlock", G_draw.block_ubo);
+}
+
+void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
+{
+  OVERLAY_PrivateData *pd = vedata->stl->pd;
+  struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
+  if (geom) {
+    DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
+  }
+}
+
+void OVERLAY_onion_skin_draw(OVERLAY_Data *vedata)
+{
+  OVERLAY_PassList *psl = vedata->psl;
+  DRW_draw_pass(psl->onion_skin_ps);
+}
\ No newline at end of file
diff --git a/source/blender/draw/engines/overlay/overlay_private.hh b/source/blender/draw/engines/overlay/overlay_private.hh
index 6c6e5cc7fbd..7825baa1dee 100644
--- a/source/blender/draw/engines/overlay/overlay_private.hh
+++ b/source/blender/draw/engines/overlay/overlay_private.hh
@@ -110,6 +110,7 @@ typedef struct OVERLAY_PassList {
   DRWPass *image_foreground_scene_ps;
   DRWPass *metaball_ps[2];
   DRWPass *motion_paths_ps;
+  DRWPass *onion_skin_ps;
   DRWPass *outlines_prepass_ps;
   DRWPass *outlines_detect_ps;
   DRWPass *outlines_resolve_ps;
@@ -276,6 +277,7 @@ typedef struct OVERLAY_PrivateData {
   DRWShadingGroup *flash_grp[2];
   DRWShadingGroup *motion_path_lines_grp;
   DRWShadingGroup *motion_path_points_grp;
+  DRWShadingGroup *onion_skin_grp;
   DRWShadingGroup *outlines_grp;
   DRWShadingGroup *outlines_curves_grp;
   DRWShadingGroup *outlines_ptcloud_grp;
@@ -649,6 +651,7 @@ void OVERLAY_image_empty_cache_populate(OVERLAY_Data *vedata, Object *ob);
 void OVERLAY_image_cache_finish(OVERLAY_Data *vedata);
 void OVERLAY_image_draw(OVERLAY_Data *vedata);
 void OVERLAY_image_background_draw(OVERLAY_Data *vedata);
+
 /**
  * This function draws images that needs the view transform applied.
  * It draws these images directly into the scene color buffer.
@@ -666,6 +669,10 @@ void OVERLAY_motion_path_cache_init(OVERLAY_Data *vedata);
 void OVERLAY_motion_path_cache_populate(OVERLAY_Data *vedata, Object *ob);
 void OVERLAY_motion_path_draw(OVERLAY_Data *vedata);
 
+void OVERLAY_onion_skin_init(OVERLAY_Data *vedata);
+void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob);
+void OVERLAY_onion_skin_draw(OVERLAY_Data *vedata);
+
 void OVERLAY_outline_init(OVERLAY_Data *vedata);
 void OVERLAY_outline_cache_init(OVERLAY_Data *vedata);
 void OVERLAY_outline_cache_populate(OVERLAY_Data *vedata,
@@ -765,6 +772,7 @@ GPUShader *OVERLAY_shader_grid_image(void);
 GPUShader *OVERLAY_shader_image(void);
 GPUShader *OVERLAY_shader_motion_path_line(void);
 GPUShader *OVERLAY_shader_motion_path_vert(void);
+GPUShader *OVERLAY_shader_onion_skin_mesh(void);
 GPUShader *OVERLAY_shader_uniform_color(void);
 GPUShader *OVERLAY_shader_uniform_color_pointcloud(void);
 GPUShader *OVERLAY_shader_outline_prepass(bool use_wire);
diff --git a/source/blender/draw/engines/overlay/overlay_shader.cc b/source/blender/draw/engines/overlay/overlay_shader.cc
index f549a66a537..4fab971516b 100644
--- a/source/blender/draw/engines/overlay/overlay_shader.cc
+++ b/source/blender/draw/engines/overlay/overlay_shader.cc
@@ -76,6 +76,7 @@ struct OVERLAY_Shaders {
   GPUShader *image;
   GPUShader *motion_path_line;
   GPUShader *motion_path_vert;
+  GPUShader *onion_skin_mesh;
   GPUShader *outline_prepass;
   GPUShader *outline_prepass_curves;
   GPUShader *outline_prepass_gpencil;
@@ -683,6 +684,16 @@ GPUShader *OVERLAY_shader_motion_path_vert(void)
   return sh_data->motion_path_vert;
 }
 
+GPUShader *OVERLAY_shader_onion_skin_mesh(void)
+{
+  const DRWContextState *draw_ctx = DRW_context_state_get();
+  OVERLAY_Shaders *sh_data = &e_data.sh_data[draw_ctx->sh_cfg];
+  if (!sh_data->onion_skin_mesh) {
+    sh_data->onion_skin_mesh = GPU_shader_create_from_info_name("overlay_onion_skin_mesh");
+  }
+  return sh_data->onion_skin_mesh;
+}
+
 GPUShader *OVERLAY_shader_outline_prepass(bool use_wire)
 {
   const DRWContextState *draw_ctx = DRW_context_state_get();
diff --git a/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh b/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh
index 9e6b6e5f737..a422734f0b5 100644
--- a/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh
+++ b/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh
@@ -247,6 +247,23 @@ GPU_SHADER_CREATE_INFO(overlay_motion_path_point_clipped)
 
 /** \} */
 
+/* -------------------------------------------------------------------- */
+/** \name Onion Skin
+ * \{ */
+
+GPU_SHADER_INTERFACE_INFO(onion_skin_iface, "interp").smooth(Type::VEC4, "color");
+
+GPU_SHADER_CREATE_INFO(overlay_onion_skin_mesh)
+    .do_static_compilation(true)
+    .vertex_in(0, Type::VEC3, "pos")
+    .vertex_out(onion_skin_iface)
+    .fragment_out(0, Type::VEC4, "fragColor")
+    .fragment_source("overlay_onion_skin_mesh_frag.glsl")
+    .vertex_source("overlay_onion_skin_mesh_vert.glsl")
+    .additional_info("draw_mesh", "draw_globals");
+
+/** \} */
+
 /* -------------------------------------------------------------------- */
 /** \name Image Empty
  * \{ */
diff --git a/source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_frag.glsl b/source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_frag.glsl
new file mode 100644
index 00000000000..dcf65b15cdf
--- /dev/null
+++ b/source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_frag.glsl
@@ -0,0 +1,4 @@
+void main()
+{
+    fragColor = interp.color;
+}
\ No newline at end of file
diff --git a/source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_vert.glsl b/source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_vert.glsl
new file mode 100644
index 00000000000..95bef155ba0
--- /dev/null
+++ b/source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_vert.glsl
@@ -0,0 +1,11 @@
+#pragma BLENDER_REQUIRE(common_view_clipping_lib.glsl)
+#pragma BLENDER_REQUIRE(common_view_lib.glsl)
+
+void main()
+{
+    interp.color.rgb = vec3(1, 0, 1);
+    interp.color.a = 0.5f;
+    vec3 world_pos = point_object_to_world(pos);
+    gl_Position = point_world_to_ndc(world_pos);
+    /* view_clipping_distances(world_pos); */
+}
\ No newline at end of file
-- 
2.30.2


From 23b6819fe4f802c5dd8fe2eab213bb1c011f2df8 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Wed, 3 May 2023 16:16:29 +0200
Subject: [PATCH 02/16] cpolor and alpha shader inputs

---
 source/blender/draw/engines/overlay/overlay_onion_skin.cc  | 7 +++++++
 .../engines/overlay/shaders/infos/overlay_extra_info.hh    | 2 ++
 .../overlay/shaders/overlay_onion_skin_mesh_vert.glsl      | 4 ++--
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/source/blender/draw/engines/overlay/overlay_onion_skin.cc b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
index 7bc672b6d05..c4c474bc573 100644
--- a/source/blender/draw/engines/overlay/overlay_onion_skin.cc
+++ b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
@@ -12,12 +12,19 @@ void OVERLAY_onion_skin_init(OVERLAY_Data *vedata)
   GPUShader *shader = OVERLAY_shader_onion_skin_mesh();
   DRWShadingGroup *grp;
   pd->onion_skin_grp = grp = DRW_shgroup_create(shader, psl->onion_skin_ps);
+
   DRW_shgroup_uniform_block(grp, "globalsBlock", G_draw.block_ubo);
 }
 
 void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
 {
   OVERLAY_PrivateData *pd = vedata->stl->pd;
+  DRWShadingGroup *grp = pd->onion_skin_grp;
+
+  float color[3] = {1, 1, 0};
+  DRW_shgroup_uniform_vec3_copy(grp, "color", color);
+  DRW_shgroup_uniform_float_copy(grp, "alpha", 0.2f);
+
   struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
   if (geom) {
     DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
diff --git a/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh b/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh
index a422734f0b5..e6d1fb53422 100644
--- a/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh
+++ b/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh
@@ -257,6 +257,8 @@ GPU_SHADER_CREATE_INFO(overlay_onion_skin_mesh)
     .do_static_compilation(true)
     .vertex_in(0, Type::VEC3, "pos")
     .vertex_out(onion_skin_iface)
+    .push_constant(Type::VEC3, "color")
+    .push_constant(Type::FLOAT, "alpha")
     .fragment_out(0, Type::VEC4, "fragColor")
     .fragment_source("overlay_onion_skin_mesh_frag.glsl")
     .vertex_source("overlay_onion_skin_mesh_vert.glsl")
diff --git a/source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_vert.glsl b/source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_vert.glsl
index 95bef155ba0..beeead0b6b9 100644
--- a/source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_vert.glsl
+++ b/source/blender/draw/engines/overlay/shaders/overlay_onion_skin_mesh_vert.glsl
@@ -3,8 +3,8 @@
 
 void main()
 {
-    interp.color.rgb = vec3(1, 0, 1);
-    interp.color.a = 0.5f;
+    interp.color.rgb = color;
+    interp.color.a = alpha;
     vec3 world_pos = point_object_to_world(pos);
     gl_Position = point_world_to_ndc(world_pos);
     /* view_clipping_distances(world_pos); */
-- 
2.30.2


From 3a439111f9562c01bc2b14d82ee84b60a2d440d1 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Thu, 4 May 2023 09:40:48 +0200
Subject: [PATCH 03/16] operators wip

---
 .../editors/animation/anim_onion_skin.c       | 41 +++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 source/blender/editors/animation/anim_onion_skin.c

diff --git a/source/blender/editors/animation/anim_onion_skin.c b/source/blender/editors/animation/anim_onion_skin.c
new file mode 100644
index 00000000000..e015b08f6ab
--- /dev/null
+++ b/source/blender/editors/animation/anim_onion_skin.c
@@ -0,0 +1,41 @@
+#include "BKE_context.h"
+#include "DNA_scene_types.h"
+#include "DNA_windowmanager_types.h"
+
+#include "ED_onion_skin.h"
+#include "MEM_guardedalloc.h"
+#include "WM_types.h"
+
+static void 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);
+  
+  BLI_freelistN(&selected);
+}
+
+static void ANIM_OT_onion_skin_add(wmOperatorType *ot)
+{
+  /* identifiers */
+  ot->name = "Add Onion Skin";
+  ot->description = "foobar";
+  ot->idname = "ANIM_OT_onion_skin_add";
+
+  /* api callbacks */
+  ot->exec = add_exec;
+  /* ot->cancel = WM_gesture_box_cancel; */
+
+  /* ot->poll = ed_markers_poll_markers_exist; */
+
+  /* flags */
+  ot->flag = OPTYPE_UNDO | OPTYPE_REGISTER;
+
+  /* properties */
+}
+
+ED_operatortypes_onion_skin(void)
+{
+  WM_operatortype_append(ANIM_OT_onion_skin_add);
+}
-- 
2.30.2


From 8fea5f23dc49906ee36c2104cd16e7c035576325 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Thu, 4 May 2023 09:41:10 +0200
Subject: [PATCH 04/16] operators wip

---
 source/blender/draw/engines/overlay/overlay_onion_skin.cc | 2 ++
 source/blender/editors/animation/CMakeLists.txt           | 1 +
 source/blender/editors/include/ED_onion_skin.h            | 2 ++
 source/blender/editors/space_api/spacetypes.c             | 2 ++
 source/blender/makesdna/DNA_scene_types.h                 | 6 ++++++
 5 files changed, 13 insertions(+)
 create mode 100644 source/blender/editors/include/ED_onion_skin.h

diff --git a/source/blender/draw/engines/overlay/overlay_onion_skin.cc b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
index c4c474bc573..4fcc87fe9be 100644
--- a/source/blender/draw/engines/overlay/overlay_onion_skin.cc
+++ b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
@@ -21,6 +21,8 @@ void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
   OVERLAY_PrivateData *pd = vedata->stl->pd;
   DRWShadingGroup *grp = pd->onion_skin_grp;
 
+  const DRWContextState *draw_ctx = DRW_context_state_get();
+
   float color[3] = {1, 1, 0};
   DRW_shgroup_uniform_vec3_copy(grp, "color", color);
   DRW_shgroup_uniform_float_copy(grp, "alpha", 0.2f);
diff --git a/source/blender/editors/animation/CMakeLists.txt b/source/blender/editors/animation/CMakeLists.txt
index 66db6eb7924..2d3e76fd863 100644
--- a/source/blender/editors/animation/CMakeLists.txt
+++ b/source/blender/editors/animation/CMakeLists.txt
@@ -29,6 +29,7 @@ set(SRC
   anim_ipo_utils.c
   anim_markers.c
   anim_motion_paths.c
+  anim_onion_skin.c
   anim_ops.c
   drivers.c
   fmodifier_ui.c
diff --git a/source/blender/editors/include/ED_onion_skin.h b/source/blender/editors/include/ED_onion_skin.h
new file mode 100644
index 00000000000..cabf3095c58
--- /dev/null
+++ b/source/blender/editors/include/ED_onion_skin.h
@@ -0,0 +1,2 @@
+
+void ED_operatortypes_onion_skin(void);
diff --git a/source/blender/editors/space_api/spacetypes.c b/source/blender/editors/space_api/spacetypes.c
index 56aa0104329..76bfb15cebf 100644
--- a/source/blender/editors/space_api/spacetypes.c
+++ b/source/blender/editors/space_api/spacetypes.c
@@ -41,6 +41,7 @@
 #include "ED_mesh.h"
 #include "ED_node.h"
 #include "ED_object.h"
+#include "ED_onion_skin.h"
 #include "ED_paint.h"
 #include "ED_physics.h"
 #include "ED_render.h"
@@ -105,6 +106,7 @@ void ED_spacetypes_init(void)
   ED_operatortypes_curves();
   ED_operatortypes_armature();
   ED_operatortypes_marker();
+  ED_operatortypes_onion_skin();
   ED_operatortypes_metaball();
   ED_operatortypes_sound();
   ED_operatortypes_render();
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 81ea41a52d2..875a865cdab 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -1875,6 +1875,11 @@ enum {
 /** \name Scene ID-Block
  * \{ */
 
+typedef struct SceneOnionSkin {
+  SceneOnionSkin *prev, *next;
+  Mesh *mesh;
+} SceneOnionSkin;
+
 typedef struct Scene {
   ID id;
   /** Animation data (must be immediately after id for utilities to use it). */
@@ -1994,6 +1999,7 @@ typedef struct Scene {
   struct SceneDisplay display;
   struct SceneEEVEE eevee;
   struct SceneGpencil grease_pencil_settings;
+  struct ListBase onion_skin_cache /* SceneOnionSkin */;
 } Scene;
 
 /** \} */
-- 
2.30.2


From f5fcc5dd0f23346bcdf2c047308d67c1cee03bf9 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Fri, 5 May 2023 10:14:59 +0200
Subject: [PATCH 05/16] wip

---
 .../draw/engines/overlay/overlay_engine.cc     |  3 +--
 .../editors/animation/anim_onion_skin.c        | 18 +++++++++++++-----
 source/blender/makesdna/DNA_scene_types.h      | 13 ++++++++++---
 3 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/source/blender/draw/engines/overlay/overlay_engine.cc b/source/blender/draw/engines/overlay/overlay_engine.cc
index 35aebd39b0e..880354b88ec 100644
--- a/source/blender/draw/engines/overlay/overlay_engine.cc
+++ b/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)
diff --git a/source/blender/editors/animation/anim_onion_skin.c b/source/blender/editors/animation/anim_onion_skin.c
index e015b08f6ab..0bd56374ab2 100644
--- a/source/blender/editors/animation/anim_onion_skin.c
+++ b/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);
 }
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 4f385a3630e..d45ebfcdffa 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/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 {
-  SceneOnionSkin *prev, *next;
+typedef struct OnionSkinMesh {
+  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;
 
 /** \} */
-- 
2.30.2


From 9d0717ba70b463e872a365996884666ce8a2b69b Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Fri, 5 May 2023 10:49:32 +0200
Subject: [PATCH 06/16] fix

---
 source/blender/makesdna/DNA_scene_types.h | 24 +++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index d45ebfcdffa..bcea007f15c 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -23,7 +23,6 @@
 #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"
 
@@ -1849,6 +1848,18 @@ typedef struct SceneGpencil {
   char _pad[4];
 } SceneGpencil;
 
+typedef struct OnionSkinMesh {
+  struct OnionSkinMesh *prev, *next;
+  /* Having a Mesh pointer here breaks compilation. Complains about "extern C" issues. */
+  void *mesh;
+} OnionSkinMesh;
+
+typedef struct SceneOnionSkin {
+  float color[3];
+  float alpha;
+  ListBase meshes /* OnionSkinMesh */;
+} SceneOnionSkin;
+
 /** \} */
 
 /* -------------------------------------------------------------------- */
@@ -1876,17 +1887,6 @@ enum {
 /** \name Scene ID-Block
  * \{ */
 
-typedef struct OnionSkinMesh {
-  struct OnionSkinMesh *prev, *next;
-  Mesh *mesh;
-} OnionSkinMesh;
-
-typedef struct SceneOnionSkin {
-  float color[3];
-  float alpha;
-  ListBase meshes /* OnionSkinMesh */;
-} SceneOnionSkin;
-
 typedef struct Scene {
   ID id;
   /** Animation data (must be immediately after id for utilities to use it). */
-- 
2.30.2


From 18d660da732d34cc3f4987cc54c7c096d66b5a13 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Fri, 5 May 2023 12:44:18 +0200
Subject: [PATCH 07/16] scene props

---
 scripts/startup/bl_ui/properties_render.py    | 25 ++++++++++++
 .../engines/overlay/overlay_onion_skin.cc     | 12 ++++--
 .../editors/animation/anim_onion_skin.c       | 38 ++++++++++++++-----
 source/blender/makesdna/DNA_scene_types.h     |  8 ++--
 source/blender/makesrna/intern/rna_scene.c    | 15 ++++++++
 source/blender/makesrna/intern/rna_space.c    |  6 ++-
 6 files changed, 85 insertions(+), 19 deletions(-)

diff --git a/scripts/startup/bl_ui/properties_render.py b/scripts/startup/bl_ui/properties_render.py
index bf3c322f377..8f9bdac9a28 100644
--- a/scripts/startup/bl_ui/properties_render.py
+++ b/scripts/startup/bl_ui/properties_render.py
@@ -715,6 +715,29 @@ class RENDER_PT_gpencil(RenderButtonsPanel, Panel):
         col.prop(props, "antialias_threshold")
 
 
+class RENDER_PT_onion_skins(RenderButtonsPanel, Panel):
+    bl_label = "Onion Skins"
+    bl_options = {'DEFAULT_CLOSED'}
+    bl_order = 10
+    COMPAT_ENGINES = {
+        'BLENDER_RENDER',
+        'BLENDER_EEVEE',
+        'BLENDER_EEVEE_NEXT',
+        'BLENDER_WORKBENCH',
+        'BLENDER_WORKBENCH_NEXT'}
+
+    def draw(self, context):
+        layout = self.layout
+        # layout.use_property_split = True
+        # layout.use_property_decorate = False  # No animation.
+
+        scene = context.scene
+
+        col = layout.column()
+        col.prop(scene, "onion_skin_color")
+        col.prop(scene, "onion_skin_alpha")
+
+
 class RENDER_PT_opengl_sampling(RenderButtonsPanel, Panel):
     bl_label = "Sampling"
     COMPAT_ENGINES = {'BLENDER_WORKBENCH', 'BLENDER_WORKBENCH_NEXT'}
@@ -921,6 +944,8 @@ classes = (
     RENDER_PT_simplify_viewport,
     RENDER_PT_simplify_render,
     RENDER_PT_simplify_greasepencil,
+
+    RENDER_PT_onion_skins,
 )
 
 if __name__ == "__main__":  # only for live edit.
diff --git a/source/blender/draw/engines/overlay/overlay_onion_skin.cc b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
index 4fcc87fe9be..ac645926418 100644
--- a/source/blender/draw/engines/overlay/overlay_onion_skin.cc
+++ b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
@@ -1,4 +1,5 @@
 #include "DRW_render.h"
+#include "draw_cache_impl.h"
 #include "overlay_private.hh"
 
 void OVERLAY_onion_skin_init(OVERLAY_Data *vedata)
@@ -23,10 +24,15 @@ void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
 
   const DRWContextState *draw_ctx = DRW_context_state_get();
 
-  float color[3] = {1, 1, 0};
-  DRW_shgroup_uniform_vec3_copy(grp, "color", color);
-  DRW_shgroup_uniform_float_copy(grp, "alpha", 0.2f);
+  DRW_shgroup_uniform_vec3_copy(grp, "color", draw_ctx->scene->onion_skin_cache.color);
+  DRW_shgroup_uniform_float_copy(grp, "alpha", draw_ctx->scene->onion_skin_cache.alpha);
 
+  /* LISTBASE_FOREACH (OnionSkinMeshLink *, mesh_link, &draw_ctx->scene->onion_skin_cache.meshes) {
+    struct GPUBatch *geom = DRW_mesh_batch_cache_get_surface((Mesh *)mesh_link->mesh);
+    if (geom) {
+      DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
+    }
+  } */
   struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
   if (geom) {
     DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
diff --git a/source/blender/editors/animation/anim_onion_skin.c b/source/blender/editors/animation/anim_onion_skin.c
index 0bd56374ab2..bfd992357ec 100644
--- a/source/blender/editors/animation/anim_onion_skin.c
+++ b/source/blender/editors/animation/anim_onion_skin.c
@@ -1,26 +1,44 @@
 #include "BKE_context.h"
+#include "BKE_lib_id.h"
+#include "BKE_mesh.h"
 #include "DNA_scene_types.h"
 #include "DNA_windowmanager_types.h"
-
 #include "ED_onion_skin.h"
 #include "MEM_guardedalloc.h"
 #include "WM_api.h"
 #include "WM_types.h"
 
-static int onion_skin_add_exec(bContext *C, wmOperator *op)
+static void graveyard()
 {
   ListBase selected = {NULL, NULL};
-  CTX_data_selected_objects(C, &selected);
+  LISTBASE_FOREACH (CollectionPointerLink *, object_ptr_link, &selected) {
+    /* Mesh *mesh = BKE_mesh_from_object(ob);
+    if (!mesh) {
+      continue;
+    } */
+    /* Mesh *copy = BKE_mesh_copy_for_eval(mesh); */
+    /* Mesh *mesh_result = (Mesh *)BKE_id_copy_ex(
+        NULL, &mesh->id, NULL, LIB_ID_CREATE_NO_MAIN | LIB_ID_CREATE_NO_USER_REFCOUNT); */
+    /*
+    OnionSkinMeshLink *link = MEM_callocN(sizeof(OnionSkinMeshLink), "onion skin mesh link");
+    link->mesh = copy;
+    BLI_addtail(&scene->onion_skin_cache.meshes, link); */
+  }
+  BLI_freelistN(&selected);
+}
+
+static int onion_skin_add_exec(bContext *C, wmOperator *op)
+{
   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);
-  }
+  Object *ob = CTX_data_active_object(C);
+  Mesh *mesh = BKE_mesh_from_object(ob);
+  Mesh *copy = BKE_mesh_copy_for_eval(mesh);
+
+  OnionSkinMeshLink *link = MEM_callocN(sizeof(OnionSkinMeshLink), "onion skin mesh link");
+  link->mesh = copy;
+  BLI_addtail(&scene->onion_skin_cache.meshes, link);
 
-  BLI_freelistN(&selected);
   return OPERATOR_FINISHED;
 }
 
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index bcea007f15c..588ec989086 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -1848,16 +1848,16 @@ typedef struct SceneGpencil {
   char _pad[4];
 } SceneGpencil;
 
-typedef struct OnionSkinMesh {
-  struct OnionSkinMesh *prev, *next;
+typedef struct OnionSkinMeshLink {
+  struct OnionSkinMeshLink *prev, *next;
   /* Having a Mesh pointer here breaks compilation. Complains about "extern C" issues. */
   void *mesh;
-} OnionSkinMesh;
+} OnionSkinMeshLink;
 
 typedef struct SceneOnionSkin {
   float color[3];
   float alpha;
-  ListBase meshes /* OnionSkinMesh */;
+  ListBase meshes /* OnionSkinMeshLink */;
 } SceneOnionSkin;
 
 /** \} */
diff --git a/source/blender/makesrna/intern/rna_scene.c b/source/blender/makesrna/intern/rna_scene.c
index 989399162e9..00dc405f360 100644
--- a/source/blender/makesrna/intern/rna_scene.c
+++ b/source/blender/makesrna/intern/rna_scene.c
@@ -8358,6 +8358,21 @@ void RNA_def_scene(BlenderRNA *brna)
   RNA_def_property_struct_type(prop, "SceneGpencil");
   RNA_def_property_ui_text(prop, "Grease Pencil", "Grease Pencil settings for the scene");
 
+  prop = RNA_def_property(srna, "onion_skin_color", PROP_FLOAT, PROP_COLOR);
+  RNA_def_property_float_sdna(prop, NULL, "onion_skin_cache.color");
+  RNA_def_property_array(prop, 3);
+  RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+  RNA_def_property_ui_text(prop, "Onion Skin Color", "Define the color of onion skins");
+  RNA_def_property_update(prop, NC_SPACE | ND_SPACE_VIEW3D | NS_VIEW3D_SHADING, NULL);
+
+  prop = RNA_def_property(srna, "onion_skin_alpha", PROP_FLOAT, PROP_FACTOR);
+  RNA_def_property_float_sdna(prop, NULL, "onion_skin_cache.alpha");
+  RNA_def_property_ui_text(prop, "Onion Skin Alpha", "Alpha of drawn onion skins");
+  RNA_def_property_range(prop, 0.0f, 1.0f);
+  RNA_def_property_ui_range(prop, 0.0f, 1.0f, 1, 2);
+  RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+  RNA_def_property_update(prop, NC_SPACE | ND_SPACE_VIEW3D | NS_VIEW3D_SHADING, NULL);
+
   /* Nestled Data. */
   /* *** Non-Animated *** */
   RNA_define_animate_sdna(false);
diff --git a/source/blender/makesrna/intern/rna_space.c b/source/blender/makesrna/intern/rna_space.c
index b8cf054aeb4..9d4fc3f584c 100644
--- a/source/blender/makesrna/intern/rna_space.c
+++ b/source/blender/makesrna/intern/rna_space.c
@@ -1541,7 +1541,8 @@ static void rna_3DViewShading_render_pass_set(PointerRNA *ptr, int value)
     BLI_strncpy(shading->aov_name, aov->name, sizeof(aov->name));
   }
   else if (value == EEVEE_RENDER_PASS_BLOOM &&
-           ((scene->eevee.flag & SCE_EEVEE_BLOOM_ENABLED) == 0)) {
+           ((scene->eevee.flag & SCE_EEVEE_BLOOM_ENABLED) == 0))
+  {
     shading->render_pass = EEVEE_RENDER_PASS_COMBINED;
   }
   else {
@@ -3298,7 +3299,8 @@ const EnumPropertyItem *rna_SpaceSpreadsheet_attribute_domain_itemf(bContext *UN
                 ATTR_DOMAIN_CORNER,
                 ATTR_DOMAIN_EDGE,
                 ATTR_DOMAIN_POINT,
-                ATTR_DOMAIN_FACE)) {
+                ATTR_DOMAIN_FACE))
+      {
         continue;
       }
     }
-- 
2.30.2


From 47a7f7e342f109dfd70b9d0ffbaa099cf4de05dd Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Fri, 5 May 2023 14:16:56 +0200
Subject: [PATCH 08/16] wip

---
 .../blender/draw/engines/overlay/overlay_onion_skin.cc   | 8 ++++----
 source/blender/editors/animation/anim_onion_skin.c       | 9 ++++++++-
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/source/blender/draw/engines/overlay/overlay_onion_skin.cc b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
index ac645926418..21c49ee13b8 100644
--- a/source/blender/draw/engines/overlay/overlay_onion_skin.cc
+++ b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
@@ -27,16 +27,16 @@ void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
   DRW_shgroup_uniform_vec3_copy(grp, "color", draw_ctx->scene->onion_skin_cache.color);
   DRW_shgroup_uniform_float_copy(grp, "alpha", draw_ctx->scene->onion_skin_cache.alpha);
 
-  /* LISTBASE_FOREACH (OnionSkinMeshLink *, mesh_link, &draw_ctx->scene->onion_skin_cache.meshes) {
+  LISTBASE_FOREACH (OnionSkinMeshLink *, mesh_link, &draw_ctx->scene->onion_skin_cache.meshes) {
     struct GPUBatch *geom = DRW_mesh_batch_cache_get_surface((Mesh *)mesh_link->mesh);
     if (geom) {
       DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
     }
-  } */
-  struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
+  }
+  /* struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
   if (geom) {
     DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
-  }
+  } */
 }
 
 void OVERLAY_onion_skin_draw(OVERLAY_Data *vedata)
diff --git a/source/blender/editors/animation/anim_onion_skin.c b/source/blender/editors/animation/anim_onion_skin.c
index bfd992357ec..03304af78b6 100644
--- a/source/blender/editors/animation/anim_onion_skin.c
+++ b/source/blender/editors/animation/anim_onion_skin.c
@@ -32,8 +32,15 @@ static int onion_skin_add_exec(bContext *C, wmOperator *op)
   Scene *scene = CTX_data_scene(C);
 
   Object *ob = CTX_data_active_object(C);
+  if (!ob) {
+    return OPERATOR_CANCELLED;
+  }
   Mesh *mesh = BKE_mesh_from_object(ob);
-  Mesh *copy = BKE_mesh_copy_for_eval(mesh);
+  if (!mesh) {
+    return OPERATOR_CANCELLED;
+  }
+  /* Mesh *copy = BKE_mesh_copy_for_eval(mesh); */
+  Mesh *copy = (Mesh *)BKE_id_copy_ex(NULL, &mesh->id, NULL, LIB_ID_COPY_LOCALIZE);
 
   OnionSkinMeshLink *link = MEM_callocN(sizeof(OnionSkinMeshLink), "onion skin mesh link");
   link->mesh = copy;
-- 
2.30.2


From 0a225f889578cceea62e3970cbea636ea7a0df80 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Fri, 19 May 2023 14:11:37 +0200
Subject: [PATCH 09/16] wip test

---
 .../engines/overlay/overlay_onion_skin.cc     | 10 ++++--
 .../editors/animation/anim_onion_skin.c       | 32 ++++++++++++++++---
 source/blender/makesdna/DNA_scene_types.h     |  4 +--
 3 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/source/blender/draw/engines/overlay/overlay_onion_skin.cc b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
index 21c49ee13b8..f31175ccc1c 100644
--- a/source/blender/draw/engines/overlay/overlay_onion_skin.cc
+++ b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
@@ -1,3 +1,4 @@
+#include "BKE_mesh.h"
 #include "DRW_render.h"
 #include "draw_cache_impl.h"
 #include "overlay_private.hh"
@@ -27,8 +28,13 @@ void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
   DRW_shgroup_uniform_vec3_copy(grp, "color", draw_ctx->scene->onion_skin_cache.color);
   DRW_shgroup_uniform_float_copy(grp, "alpha", draw_ctx->scene->onion_skin_cache.alpha);
 
-  LISTBASE_FOREACH (OnionSkinMeshLink *, mesh_link, &draw_ctx->scene->onion_skin_cache.meshes) {
-    struct GPUBatch *geom = DRW_mesh_batch_cache_get_surface((Mesh *)mesh_link->mesh);
+  LISTBASE_FOREACH (OnionSkinMeshLink *, mesh_link, &draw_ctx->scene->onion_skin_cache.objects) {
+    if (ob != mesh_link->object) {
+      continue;
+    }
+    Mesh *mesh = BKE_mesh_from_object(ob);
+
+    struct GPUBatch *geom = DRW_mesh_batch_cache_get_surface(mesh);
     if (geom) {
       DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
     }
diff --git a/source/blender/editors/animation/anim_onion_skin.c b/source/blender/editors/animation/anim_onion_skin.c
index 03304af78b6..2c21e1f2be4 100644
--- a/source/blender/editors/animation/anim_onion_skin.c
+++ b/source/blender/editors/animation/anim_onion_skin.c
@@ -1,9 +1,15 @@
 #include "BKE_context.h"
+#include "BKE_layer.h"
 #include "BKE_lib_id.h"
+#include "BKE_main.h"
 #include "BKE_mesh.h"
+#include "BKE_object.h"
+#include "DEG_depsgraph.h"
+#include "DEG_depsgraph_build.h"
 #include "DNA_scene_types.h"
 #include "DNA_windowmanager_types.h"
 #include "ED_onion_skin.h"
+#include "ED_outliner.h"
 #include "MEM_guardedalloc.h"
 #include "WM_api.h"
 #include "WM_types.h"
@@ -30,6 +36,9 @@ static void graveyard()
 static int onion_skin_add_exec(bContext *C, wmOperator *op)
 {
   Scene *scene = CTX_data_scene(C);
+  Main *bmain = CTX_data_main(C);
+  BKE_main_id_newptr_and_tag_clear(bmain);
+  ViewLayer *view_layer = CTX_data_view_layer(C);
 
   Object *ob = CTX_data_active_object(C);
   if (!ob) {
@@ -40,11 +49,26 @@ static int onion_skin_add_exec(bContext *C, wmOperator *op)
     return OPERATOR_CANCELLED;
   }
   /* Mesh *copy = BKE_mesh_copy_for_eval(mesh); */
-  Mesh *copy = (Mesh *)BKE_id_copy_ex(NULL, &mesh->id, NULL, LIB_ID_COPY_LOCALIZE);
-
+  /* Mesh *copy = (Mesh *)BKE_id_copy_ex(bmain, &mesh->id, NULL, LIB_ID_COPY_DEFAULT); */
+  Object *ob_new = BKE_object_duplicate(bmain,
+                                        ob,
+                                        (eDupli_ID_Flags)U.dupflag,
+                                        LIB_ID_DUPLICATE_IS_SUBPROCESS |
+                                            LIB_ID_DUPLICATE_IS_ROOT_ID);
+  LayerCollection *layer_collection = BKE_layer_collection_from_index(view_layer, 2);
+  BKE_collection_object_add(bmain, layer_collection->collection, ob_new);
   OnionSkinMeshLink *link = MEM_callocN(sizeof(OnionSkinMeshLink), "onion skin mesh link");
-  link->mesh = copy;
-  BLI_addtail(&scene->onion_skin_cache.meshes, link);
+  link->object = ob_new;
+  ob_new->adt = NULL;
+  BLI_addtail(&scene->onion_skin_cache.objects, link);
+
+  ED_outliner_select_sync_from_object_tag(C);
+
+  DEG_relations_tag_update(bmain);
+  DEG_id_tag_update(&scene->id, ID_RECALC_COPY_ON_WRITE | ID_RECALC_SELECT);
+
+  WM_event_add_notifier(C, NC_SCENE | ND_OB_SELECT, scene);
+  WM_event_add_notifier(C, NC_SCENE | ND_LAYER_CONTENT, scene);
 
   return OPERATOR_FINISHED;
 }
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 4796b77823f..99b5e1225aa 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -1852,13 +1852,13 @@ typedef struct SceneGpencil {
 typedef struct OnionSkinMeshLink {
   struct OnionSkinMeshLink *prev, *next;
   /* Having a Mesh pointer here breaks compilation. Complains about "extern C" issues. */
-  void *mesh;
+  struct Object *object;
 } OnionSkinMeshLink;
 
 typedef struct SceneOnionSkin {
   float color[3];
   float alpha;
-  ListBase meshes /* OnionSkinMeshLink */;
+  ListBase objects /* OnionSkinMeshLink */;
 } SceneOnionSkin;
 
 /** \} */
-- 
2.30.2


From 1dc4512cdeff62d98794a64f6206c992fda0ce46 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Sun, 21 May 2023 13:22:33 +0200
Subject: [PATCH 10/16] hacky implementation

---
 .../engines/overlay/overlay_onion_skin.cc     | 25 ++++++++++++++-----
 .../editors/animation/anim_onion_skin.c       |  3 +--
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/source/blender/draw/engines/overlay/overlay_onion_skin.cc b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
index f31175ccc1c..21630406b62 100644
--- a/source/blender/draw/engines/overlay/overlay_onion_skin.cc
+++ b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
@@ -18,6 +18,17 @@ void OVERLAY_onion_skin_init(OVERLAY_Data *vedata)
   DRW_shgroup_uniform_block(grp, "globalsBlock", G_draw.block_ubo);
 }
 
+static bool str_equals(const char *__restrict str, const char *__restrict start)
+{
+  for (; *str && *start; str++, start++) {
+    if (*str != *start) {
+      return false;
+    }
+  }
+
+  return (*start == *str);
+}
+
 void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
 {
   OVERLAY_PrivateData *pd = vedata->stl->pd;
@@ -29,20 +40,22 @@ void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
   DRW_shgroup_uniform_float_copy(grp, "alpha", draw_ctx->scene->onion_skin_cache.alpha);
 
   LISTBASE_FOREACH (OnionSkinMeshLink *, mesh_link, &draw_ctx->scene->onion_skin_cache.objects) {
-    if (ob != mesh_link->object) {
+    // if(BKE_id_comp)
+
+    if (!str_equals(ob->id.name, mesh_link->object->id.name)) {
       continue;
     }
-    Mesh *mesh = BKE_mesh_from_object(ob);
+    /* Mesh *mesh = BKE_mesh_from_object(ob);
 
     struct GPUBatch *geom = DRW_mesh_batch_cache_get_surface(mesh);
+    if (geom) {
+      DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
+    } */
+    struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
     if (geom) {
       DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
     }
   }
-  /* struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
-  if (geom) {
-    DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
-  } */
 }
 
 void OVERLAY_onion_skin_draw(OVERLAY_Data *vedata)
diff --git a/source/blender/editors/animation/anim_onion_skin.c b/source/blender/editors/animation/anim_onion_skin.c
index 2c21e1f2be4..d8518743400 100644
--- a/source/blender/editors/animation/anim_onion_skin.c
+++ b/source/blender/editors/animation/anim_onion_skin.c
@@ -67,8 +67,7 @@ static int onion_skin_add_exec(bContext *C, wmOperator *op)
   DEG_relations_tag_update(bmain);
   DEG_id_tag_update(&scene->id, ID_RECALC_COPY_ON_WRITE | ID_RECALC_SELECT);
 
-  WM_event_add_notifier(C, NC_SCENE | ND_OB_SELECT, scene);
-  WM_event_add_notifier(C, NC_SCENE | ND_LAYER_CONTENT, scene);
+  WM_event_add_notifier(C, NC_SCENE | ND_OB_SELECT | ND_LAYER_CONTENT, scene);
 
   return OPERATOR_FINISHED;
 }
-- 
2.30.2


From ea6670404f5407e395c7eac9d5319050eee40f14 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Thu, 25 May 2023 15:10:12 +0200
Subject: [PATCH 11/16] onion skin range stuff

---
 .../keyconfig/keymap_data/blender_default.py  |   1 +
 source/blender/editors/animation/anim_ops.c   | 148 ++++++++++++++++++
 .../blender/editors/animation/time_scrub_ui.c |  35 +++++
 source/blender/makesdna/DNA_scene_types.h     |   1 +
 4 files changed, 185 insertions(+)

diff --git a/scripts/presets/keyconfig/keymap_data/blender_default.py b/scripts/presets/keyconfig/keymap_data/blender_default.py
index 9459c5eb122..65b53def66a 100644
--- a/scripts/presets/keyconfig/keymap_data/blender_default.py
+++ b/scripts/presets/keyconfig/keymap_data/blender_default.py
@@ -1056,6 +1056,7 @@ def km_time_scrub(_params):
 
     items.extend([
         ("anim.change_frame", {"type": 'LEFTMOUSE', "value": 'PRESS'}, None),
+        ("anim.change_onion_skin_range", {"type": 'LEFTMOUSE', "value": 'PRESS', "alt": True}, None),
     ])
 
     return keymap
diff --git a/source/blender/editors/animation/anim_ops.c b/source/blender/editors/animation/anim_ops.c
index 22c9217dc35..3a6c8bae7e3 100644
--- a/source/blender/editors/animation/anim_ops.c
+++ b/source/blender/editors/animation/anim_ops.c
@@ -395,6 +395,153 @@ static void ANIM_OT_change_frame(wmOperatorType *ot)
 
 /** \} */
 
+/* Set the new frame number */
+static void change_onion_skin_range_apply(bContext *C, wmOperator *op, const bool always_update)
+{
+  Scene *scene = CTX_data_scene(C);
+  const int left = RNA_int_get(op->ptr, "left");
+  const int right = RNA_int_get(op->ptr, "right");
+
+  scene->onion_skin_cache.relative_left = left;
+  scene->onion_skin_cache.relative_right = right;
+
+  /* do updates */
+  if (always_update) {
+    DEG_id_tag_update(&scene->id, ID_RECALC_FRAME_CHANGE);
+    WM_event_add_notifier(C, NC_SCENE | ND_FRAME, scene);
+  }
+}
+
+static void change_onion_skin_range_cancel(bContext *C, wmOperator *UNUSED(op))
+{
+  bScreen *screen = CTX_wm_screen(C);
+  screen->scrubbing = false;
+
+  SpaceSeq *sseq = CTX_wm_space_seq(C);
+  if (sseq != NULL) {
+    change_frame_seq_preview_end(sseq);
+  }
+
+  if (need_extra_redraw_after_scrubbing_ends(C)) {
+    Scene *scene = CTX_data_scene(C);
+    WM_event_add_notifier(C, NC_SCENE | ND_FRAME, scene);
+  }
+}
+
+/* Modal event handling of frame changing */
+static int change_onion_skin_range_modal(bContext *C, wmOperator *op, const wmEvent *event)
+{
+  int ret = OPERATOR_RUNNING_MODAL;
+  /* execute the events */
+  switch (event->type) {
+    case EVT_ESCKEY:
+      ret = OPERATOR_FINISHED;
+      break;
+
+    case MOUSEMOVE:
+      Scene *scene = CTX_data_scene(C);
+      const int clicked_frame = roundf(frame_from_event(C, event));
+      const int current_scene_frame = BKE_scene_ctime_get(scene);
+      if (clicked_frame > current_scene_frame) {
+        RNA_int_set(op->ptr, "right", clicked_frame);
+      }
+      else if (clicked_frame < current_scene_frame) {
+        RNA_int_set(op->ptr, "left", clicked_frame);
+      }
+      else {
+        return OPERATOR_CANCELLED;
+      }
+      change_onion_skin_range_apply(C, op, false);
+      break;
+
+    case LEFTMOUSE:
+    case RIGHTMOUSE:
+    case MIDDLEMOUSE:
+      /* We check for either mouse-button to end, to work with all user keymaps. */
+      if (event->val == KM_RELEASE) {
+        ret = OPERATOR_FINISHED;
+      }
+      break;
+  }
+
+  if (ret != OPERATOR_RUNNING_MODAL) {
+    bScreen *screen = CTX_wm_screen(C);
+    screen->scrubbing = false;
+
+    SpaceSeq *sseq = CTX_wm_space_seq(C);
+    if (sseq != NULL) {
+      change_frame_seq_preview_end(sseq);
+    }
+    if (need_extra_redraw_after_scrubbing_ends(C)) {
+      Scene *scene = CTX_data_scene(C);
+      WM_event_add_notifier(C, NC_SCENE | ND_FRAME, scene);
+    }
+  }
+
+  return ret;
+}
+
+/* Modal Operator init */
+static int change_onion_skin_range_invoke(bContext *C, wmOperator *op, const wmEvent *event)
+{
+  ARegion *region = CTX_wm_region(C);
+  bScreen *screen = CTX_wm_screen(C);
+  if (CTX_wm_space_seq(C) != NULL && region->regiontype == RGN_TYPE_PREVIEW) {
+    return OPERATOR_CANCELLED;
+  }
+
+  Scene *scene = CTX_data_scene(C);
+  RNA_int_set(op->ptr, "right", scene->onion_skin_cache.relative_right);
+  RNA_int_set(op->ptr, "left", scene->onion_skin_cache.relative_left);
+
+  const int clicked_frame = roundf(frame_from_event(C, event));
+  const int current_scene_frame = BKE_scene_ctime_get(scene);
+  if (clicked_frame > current_scene_frame) {
+    RNA_int_set(op->ptr, "right", clicked_frame);
+  }
+  else if (clicked_frame < current_scene_frame) {
+    RNA_int_set(op->ptr, "left", clicked_frame);
+  }
+  else {
+    return OPERATOR_CANCELLED;
+  }
+
+  screen->scrubbing = true;
+
+  change_onion_skin_range_apply(C, op, true);
+
+  /* add temp handler */
+  WM_event_add_modal_handler(C, op);
+
+  return OPERATOR_RUNNING_MODAL;
+}
+
+static int change_onion_skin_range_exec(bContext *C, wmOperator *op)
+{
+  change_onion_skin_range_apply(C, op, true);
+  return OPERATOR_FINISHED;
+}
+
+static void ANIM_OT_change_onion_skin_range(wmOperatorType *ot)
+{
+  /* identifiers */
+  ot->name = "Change Onion Skin Range";
+  ot->idname = "ANIM_OT_change_onion_skin_range";
+  ot->description = "Interactively change the amount of onion skins shown";
+
+  ot->exec = change_onion_skin_range_exec;
+  ot->poll = change_frame_poll;
+  ot->invoke = change_onion_skin_range_invoke;
+  ot->modal = change_onion_skin_range_modal;
+  ot->cancel = change_onion_skin_range_cancel;
+
+  /* rna */
+  ot->prop = RNA_def_int(
+      ot->srna, "left", 0, MINAFRAME, MAXFRAME, "Left", "", MINAFRAME, MAXFRAME);
+  ot->prop = RNA_def_int(
+      ot->srna, "right", 0, MINAFRAME, MAXFRAME, "Right", "", MINAFRAME, MAXFRAME);
+}
+
 /* -------------------------------------------------------------------- */
 /** \name Start/End Frame Operators
  * \{ */
@@ -652,6 +799,7 @@ void ED_operatortypes_anim(void)
 {
   /* Animation Editors only -------------------------- */
   WM_operatortype_append(ANIM_OT_change_frame);
+  WM_operatortype_append(ANIM_OT_change_onion_skin_range);
 
   WM_operatortype_append(ANIM_OT_start_frame_set);
   WM_operatortype_append(ANIM_OT_end_frame_set);
diff --git a/source/blender/editors/animation/time_scrub_ui.c b/source/blender/editors/animation/time_scrub_ui.c
index 5b7eee00521..10bb3ff4a0f 100644
--- a/source/blender/editors/animation/time_scrub_ui.c
+++ b/source/blender/editors/animation/time_scrub_ui.c
@@ -136,6 +136,41 @@ static void draw_current_frame(const Scene *scene,
       U.pixelsize,
       4 * UI_SCALE_FAC);
 
+  if (scene->onion_skin_cache.relative_left != 0) {
+    const int frame_relative_left = UI_view2d_view_to_region_x(
+        v2d, current_frame - scene->onion_skin_cache.relative_left);
+    UI_draw_roundbox_4fv_ex(
+        &(const rctf){
+            .xmin = frame_relative_left - box_width / 4 + U.pixelsize / 2,
+            .xmax = frame_relative_left + box_width / 4 + U.pixelsize / 2,
+            .ymin = scrub_region_rect->ymin + box_padding,
+            .ymax = scrub_region_rect->ymax - box_padding,
+        },
+        bg_color,
+        NULL,
+        1.0f,
+        outline_color,
+        U.pixelsize,
+        4 * UI_SCALE_FAC);
+  }
+  if (scene->onion_skin_cache.relative_right != 0) {
+    const int frame_relative_right = UI_view2d_view_to_region_x(
+        v2d, current_frame - scene->onion_skin_cache.relative_right);
+    UI_draw_roundbox_4fv_ex(
+        &(const rctf){
+            .xmin = frame_relative_right - box_width / 4 + U.pixelsize / 2,
+            .xmax = frame_relative_right + box_width / 4 + U.pixelsize / 2,
+            .ymin = scrub_region_rect->ymin + box_padding,
+            .ymax = scrub_region_rect->ymax - box_padding,
+        },
+        bg_color,
+        NULL,
+        1.0f,
+        outline_color,
+        U.pixelsize,
+        4 * UI_SCALE_FAC);
+  }
+
   uchar text_color[4];
   UI_GetThemeColor4ubv(TH_HEADER_TEXT_HI, text_color);
   UI_fontstyle_draw_simple(fstyle,
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index be1e978127e..8f9b9b515e2 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -1866,6 +1866,7 @@ typedef struct OnionSkinMeshLink {
 typedef struct SceneOnionSkin {
   float color[3];
   float alpha;
+  int relative_left, relative_right;
   ListBase objects /* OnionSkinMeshLink */;
 } SceneOnionSkin;
 
-- 
2.30.2


From 49a320d236fad3068c92f758bf88ea5b61241226 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Thu, 25 May 2023 15:48:13 +0200
Subject: [PATCH 12/16] fix update issue

---
 source/blender/editors/animation/anim_ops.c   | 55 +++++++------------
 .../blender/editors/animation/time_scrub_ui.c |  2 +-
 2 files changed, 21 insertions(+), 36 deletions(-)

diff --git a/source/blender/editors/animation/anim_ops.c b/source/blender/editors/animation/anim_ops.c
index 3a6c8bae7e3..4371d19315d 100644
--- a/source/blender/editors/animation/anim_ops.c
+++ b/source/blender/editors/animation/anim_ops.c
@@ -396,7 +396,7 @@ static void ANIM_OT_change_frame(wmOperatorType *ot)
 /** \} */
 
 /* Set the new frame number */
-static void change_onion_skin_range_apply(bContext *C, wmOperator *op, const bool always_update)
+static void change_onion_skin_range_apply(bContext *C, wmOperator *op)
 {
   Scene *scene = CTX_data_scene(C);
   const int left = RNA_int_get(op->ptr, "left");
@@ -405,10 +405,20 @@ static void change_onion_skin_range_apply(bContext *C, wmOperator *op, const boo
   scene->onion_skin_cache.relative_left = left;
   scene->onion_skin_cache.relative_right = right;
 
-  /* do updates */
-  if (always_update) {
-    DEG_id_tag_update(&scene->id, ID_RECALC_FRAME_CHANGE);
-    WM_event_add_notifier(C, NC_SCENE | ND_FRAME, scene);
+  DEG_id_tag_update(&scene->id, ID_RECALC_FRAME_CHANGE);
+  WM_event_add_notifier(C, NC_SCENE | ND_FRAME, scene);
+}
+
+static void onion_skin_range_foo(bContext *C, wmOperator *op, const wmEvent *event)
+{
+  Scene *scene = CTX_data_scene(C);
+  const int clicked_frame = roundf(frame_from_event(C, event));
+  const int current_scene_frame = BKE_scene_ctime_get(scene);
+  if (clicked_frame > current_scene_frame) {
+    RNA_int_set(op->ptr, "right", clicked_frame - current_scene_frame);
+  }
+  else if (clicked_frame < current_scene_frame) {
+    RNA_int_set(op->ptr, "left", current_scene_frame - clicked_frame);
   }
 }
 
@@ -439,19 +449,8 @@ static int change_onion_skin_range_modal(bContext *C, wmOperator *op, const wmEv
       break;
 
     case MOUSEMOVE:
-      Scene *scene = CTX_data_scene(C);
-      const int clicked_frame = roundf(frame_from_event(C, event));
-      const int current_scene_frame = BKE_scene_ctime_get(scene);
-      if (clicked_frame > current_scene_frame) {
-        RNA_int_set(op->ptr, "right", clicked_frame);
-      }
-      else if (clicked_frame < current_scene_frame) {
-        RNA_int_set(op->ptr, "left", clicked_frame);
-      }
-      else {
-        return OPERATOR_CANCELLED;
-      }
-      change_onion_skin_range_apply(C, op, false);
+      onion_skin_range_foo(C, op, event);
+      change_onion_skin_range_apply(C, op);
       break;
 
     case LEFTMOUSE:
@@ -468,10 +467,6 @@ static int change_onion_skin_range_modal(bContext *C, wmOperator *op, const wmEv
     bScreen *screen = CTX_wm_screen(C);
     screen->scrubbing = false;
 
-    SpaceSeq *sseq = CTX_wm_space_seq(C);
-    if (sseq != NULL) {
-      change_frame_seq_preview_end(sseq);
-    }
     if (need_extra_redraw_after_scrubbing_ends(C)) {
       Scene *scene = CTX_data_scene(C);
       WM_event_add_notifier(C, NC_SCENE | ND_FRAME, scene);
@@ -494,21 +489,11 @@ static int change_onion_skin_range_invoke(bContext *C, wmOperator *op, const wmE
   RNA_int_set(op->ptr, "right", scene->onion_skin_cache.relative_right);
   RNA_int_set(op->ptr, "left", scene->onion_skin_cache.relative_left);
 
-  const int clicked_frame = roundf(frame_from_event(C, event));
-  const int current_scene_frame = BKE_scene_ctime_get(scene);
-  if (clicked_frame > current_scene_frame) {
-    RNA_int_set(op->ptr, "right", clicked_frame);
-  }
-  else if (clicked_frame < current_scene_frame) {
-    RNA_int_set(op->ptr, "left", clicked_frame);
-  }
-  else {
-    return OPERATOR_CANCELLED;
-  }
+  onion_skin_range_foo(C, op, event);
 
   screen->scrubbing = true;
 
-  change_onion_skin_range_apply(C, op, true);
+  change_onion_skin_range_apply(C, op);
 
   /* add temp handler */
   WM_event_add_modal_handler(C, op);
@@ -518,7 +503,7 @@ static int change_onion_skin_range_invoke(bContext *C, wmOperator *op, const wmE
 
 static int change_onion_skin_range_exec(bContext *C, wmOperator *op)
 {
-  change_onion_skin_range_apply(C, op, true);
+  change_onion_skin_range_apply(C, op);
   return OPERATOR_FINISHED;
 }
 
diff --git a/source/blender/editors/animation/time_scrub_ui.c b/source/blender/editors/animation/time_scrub_ui.c
index 10bb3ff4a0f..0d2965ae946 100644
--- a/source/blender/editors/animation/time_scrub_ui.c
+++ b/source/blender/editors/animation/time_scrub_ui.c
@@ -155,7 +155,7 @@ static void draw_current_frame(const Scene *scene,
   }
   if (scene->onion_skin_cache.relative_right != 0) {
     const int frame_relative_right = UI_view2d_view_to_region_x(
-        v2d, current_frame - scene->onion_skin_cache.relative_right);
+        v2d, current_frame + scene->onion_skin_cache.relative_right);
     UI_draw_roundbox_4fv_ex(
         &(const rctf){
             .xmin = frame_relative_right - box_width / 4 + U.pixelsize / 2,
-- 
2.30.2


From 80a4e7b010da9d8bd90ced0064b1c4b2a7efb5bc Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Thu, 25 May 2023 15:52:08 +0200
Subject: [PATCH 13/16] change draw call order

---
 .../blender/editors/animation/time_scrub_ui.c | 28 +++++++++----------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/source/blender/editors/animation/time_scrub_ui.c b/source/blender/editors/animation/time_scrub_ui.c
index 0d2965ae946..4a299ba51e8 100644
--- a/source/blender/editors/animation/time_scrub_ui.c
+++ b/source/blender/editors/animation/time_scrub_ui.c
@@ -122,20 +122,6 @@ static void draw_current_frame(const Scene *scene,
   float outline_color[4];
   UI_GetThemeColorShade4fv(TH_CFRAME, 5, outline_color);
 
-  UI_draw_roundbox_4fv_ex(
-      &(const rctf){
-          .xmin = frame_x - box_width / 2 + U.pixelsize / 2,
-          .xmax = frame_x + box_width / 2 + U.pixelsize / 2,
-          .ymin = scrub_region_rect->ymin + box_padding,
-          .ymax = scrub_region_rect->ymax - box_padding,
-      },
-      bg_color,
-      NULL,
-      1.0f,
-      outline_color,
-      U.pixelsize,
-      4 * UI_SCALE_FAC);
-
   if (scene->onion_skin_cache.relative_left != 0) {
     const int frame_relative_left = UI_view2d_view_to_region_x(
         v2d, current_frame - scene->onion_skin_cache.relative_left);
@@ -171,6 +157,20 @@ static void draw_current_frame(const Scene *scene,
         4 * UI_SCALE_FAC);
   }
 
+  UI_draw_roundbox_4fv_ex(
+      &(const rctf){
+          .xmin = frame_x - box_width / 2 + U.pixelsize / 2,
+          .xmax = frame_x + box_width / 2 + U.pixelsize / 2,
+          .ymin = scrub_region_rect->ymin + box_padding,
+          .ymax = scrub_region_rect->ymax - box_padding,
+      },
+      bg_color,
+      NULL,
+      1.0f,
+      outline_color,
+      U.pixelsize,
+      4 * UI_SCALE_FAC);
+
   uchar text_color[4];
   UI_GetThemeColor4ubv(TH_HEADER_TEXT_HI, text_color);
   UI_fontstyle_draw_simple(fstyle,
-- 
2.30.2


From ba45e6bca3e44d1b0b6db303f5aaeb08c4fcc7d3 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Thu, 25 May 2023 16:57:17 +0200
Subject: [PATCH 14/16] onion skin drawing relative to current frame

---
 .../draw/engines/overlay/overlay_onion_skin.cc | 18 +++++++++++-------
 .../editors/animation/anim_onion_skin.c        |  2 ++
 source/blender/makesdna/DNA_scene_types.h      |  2 ++
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/source/blender/draw/engines/overlay/overlay_onion_skin.cc b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
index 21630406b62..4da0575e1cd 100644
--- a/source/blender/draw/engines/overlay/overlay_onion_skin.cc
+++ b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
@@ -39,18 +39,22 @@ void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
   DRW_shgroup_uniform_vec3_copy(grp, "color", draw_ctx->scene->onion_skin_cache.color);
   DRW_shgroup_uniform_float_copy(grp, "alpha", draw_ctx->scene->onion_skin_cache.alpha);
 
-  LISTBASE_FOREACH (OnionSkinMeshLink *, mesh_link, &draw_ctx->scene->onion_skin_cache.objects) {
-    // if(BKE_id_comp)
+  Scene *scene = draw_ctx->scene;
+  const float current_frame = BKE_scene_ctime_get(scene);
 
+  LISTBASE_FOREACH (OnionSkinMeshLink *, mesh_link, &scene->onion_skin_cache.objects) {
     if (!str_equals(ob->id.name, mesh_link->object->id.name)) {
       continue;
     }
-    /* Mesh *mesh = BKE_mesh_from_object(ob);
 
-    struct GPUBatch *geom = DRW_mesh_batch_cache_get_surface(mesh);
-    if (geom) {
-      DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
-    } */
+    if (mesh_link->frame < current_frame - scene->onion_skin_cache.relative_left) {
+      continue;
+    }
+
+    if (mesh_link->frame > current_frame + scene->onion_skin_cache.relative_right) {
+      continue;
+    }
+
     struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
     if (geom) {
       DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
diff --git a/source/blender/editors/animation/anim_onion_skin.c b/source/blender/editors/animation/anim_onion_skin.c
index d8518743400..441a58c46fe 100644
--- a/source/blender/editors/animation/anim_onion_skin.c
+++ b/source/blender/editors/animation/anim_onion_skin.c
@@ -4,6 +4,7 @@
 #include "BKE_main.h"
 #include "BKE_mesh.h"
 #include "BKE_object.h"
+#include "BKE_scene.h"
 #include "DEG_depsgraph.h"
 #include "DEG_depsgraph_build.h"
 #include "DNA_scene_types.h"
@@ -60,6 +61,7 @@ static int onion_skin_add_exec(bContext *C, wmOperator *op)
   OnionSkinMeshLink *link = MEM_callocN(sizeof(OnionSkinMeshLink), "onion skin mesh link");
   link->object = ob_new;
   ob_new->adt = NULL;
+  link->frame = BKE_scene_ctime_get(scene);
   BLI_addtail(&scene->onion_skin_cache.objects, link);
 
   ED_outliner_select_sync_from_object_tag(C);
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 8f9b9b515e2..62337e1293a 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -1861,6 +1861,8 @@ typedef struct OnionSkinMeshLink {
   struct OnionSkinMeshLink *prev, *next;
   /* Having a Mesh pointer here breaks compilation. Complains about "extern C" issues. */
   struct Object *object;
+  float frame;
+  char _pad[4];
 } OnionSkinMeshLink;
 
 typedef struct SceneOnionSkin {
-- 
2.30.2


From bc0d9a18b72f09cfcf639e76f77d2f13813cad26 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Fri, 26 May 2023 16:57:49 +0200
Subject: [PATCH 15/16] left and right color. not working properly

---
 scripts/startup/bl_ui/properties_render.py    |  5 +++-
 .../engines/overlay/overlay_onion_skin.cc     | 17 +++++++++---
 source/blender/makesdna/DNA_scene_types.h     |  4 ++-
 source/blender/makesrna/intern/rna_scene.c    | 27 ++++++++++++++++---
 4 files changed, 44 insertions(+), 9 deletions(-)

diff --git a/scripts/startup/bl_ui/properties_render.py b/scripts/startup/bl_ui/properties_render.py
index 8f9bdac9a28..6d9def40e2a 100644
--- a/scripts/startup/bl_ui/properties_render.py
+++ b/scripts/startup/bl_ui/properties_render.py
@@ -734,7 +734,10 @@ class RENDER_PT_onion_skins(RenderButtonsPanel, Panel):
         scene = context.scene
 
         col = layout.column()
-        col.prop(scene, "onion_skin_color")
+        col.prop(scene, "onion_skin_color_left")
+        col.prop(scene, "onion_skin_color_right")
+        col.prop(scene, "os_relative_left")
+        col.prop(scene, "os_relative_right")
         col.prop(scene, "onion_skin_alpha")
 
 
diff --git a/source/blender/draw/engines/overlay/overlay_onion_skin.cc b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
index 4da0575e1cd..dd39a726669 100644
--- a/source/blender/draw/engines/overlay/overlay_onion_skin.cc
+++ b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
@@ -36,17 +36,20 @@ void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
 
   const DRWContextState *draw_ctx = DRW_context_state_get();
 
-  DRW_shgroup_uniform_vec3_copy(grp, "color", draw_ctx->scene->onion_skin_cache.color);
-  DRW_shgroup_uniform_float_copy(grp, "alpha", draw_ctx->scene->onion_skin_cache.alpha);
-
   Scene *scene = draw_ctx->scene;
   const float current_frame = BKE_scene_ctime_get(scene);
 
+  DRW_shgroup_uniform_float_copy(grp, "alpha", draw_ctx->scene->onion_skin_cache.alpha);
+
   LISTBASE_FOREACH (OnionSkinMeshLink *, mesh_link, &scene->onion_skin_cache.objects) {
     if (!str_equals(ob->id.name, mesh_link->object->id.name)) {
       continue;
     }
 
+    if (compare_ff(mesh_link->frame, current_frame, FLT_EPSILON)) {
+      continue;
+    }
+
     if (mesh_link->frame < current_frame - scene->onion_skin_cache.relative_left) {
       continue;
     }
@@ -54,10 +57,16 @@ void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
     if (mesh_link->frame > current_frame + scene->onion_skin_cache.relative_right) {
       continue;
     }
+    if (mesh_link->frame < current_frame) {
+      DRW_shgroup_uniform_vec3_copy(grp, "color", draw_ctx->scene->onion_skin_cache.color_left);
+    }
+    else {
+      DRW_shgroup_uniform_vec3_copy(grp, "color", draw_ctx->scene->onion_skin_cache.color_right);
+    }
 
     struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
     if (geom) {
-      DRW_shgroup_call(pd->onion_skin_grp, geom, ob);
+      DRW_shgroup_call(grp, geom, ob);
     }
   }
 }
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 62337e1293a..28a835cd580 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -1866,9 +1866,11 @@ typedef struct OnionSkinMeshLink {
 } OnionSkinMeshLink;
 
 typedef struct SceneOnionSkin {
-  float color[3];
+  float color_left[3];
+  float color_right[3];
   float alpha;
   int relative_left, relative_right;
+  char _pad[4];
   ListBase objects /* OnionSkinMeshLink */;
 } SceneOnionSkin;
 
diff --git a/source/blender/makesrna/intern/rna_scene.c b/source/blender/makesrna/intern/rna_scene.c
index 7a3923c6bba..b5253ad5395 100644
--- a/source/blender/makesrna/intern/rna_scene.c
+++ b/source/blender/makesrna/intern/rna_scene.c
@@ -8442,11 +8442,32 @@ void RNA_def_scene(BlenderRNA *brna)
   RNA_def_property_struct_type(prop, "SceneGpencil");
   RNA_def_property_ui_text(prop, "Grease Pencil", "Grease Pencil settings for the scene");
 
-  prop = RNA_def_property(srna, "onion_skin_color", PROP_FLOAT, PROP_COLOR);
-  RNA_def_property_float_sdna(prop, NULL, "onion_skin_cache.color");
+  prop = RNA_def_property(srna, "onion_skin_color_left", PROP_FLOAT, PROP_COLOR);
+  RNA_def_property_float_sdna(prop, NULL, "onion_skin_cache.color_left");
   RNA_def_property_array(prop, 3);
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
-  RNA_def_property_ui_text(prop, "Onion Skin Color", "Define the color of onion skins");
+  RNA_def_property_ui_text(prop, "Onion Skin Color Left", "Define the color of onion skins");
+  RNA_def_property_update(prop, NC_SPACE | ND_SPACE_VIEW3D | NS_VIEW3D_SHADING, NULL);
+
+  prop = RNA_def_property(srna, "onion_skin_color_right", PROP_FLOAT, PROP_COLOR);
+  RNA_def_property_float_sdna(prop, NULL, "onion_skin_cache.color_right");
+  RNA_def_property_array(prop, 3);
+  RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+  RNA_def_property_ui_text(prop, "Onion Skin Color Right", "Define the color of onion skins");
+  RNA_def_property_update(prop, NC_SPACE | ND_SPACE_VIEW3D | NS_VIEW3D_SHADING, NULL);
+
+  prop = RNA_def_property(srna, "os_relative_left", PROP_INT, PROP_UNSIGNED);
+  RNA_def_property_int_sdna(prop, NULL, "onion_skin_cache.relative_left");
+  RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+  RNA_def_property_ui_text(
+      prop, "Onion Skin Range Left", "how far to the lef to draw onion skins");
+  RNA_def_property_update(prop, NC_SPACE | ND_SPACE_VIEW3D | NS_VIEW3D_SHADING, NULL);
+
+  prop = RNA_def_property(srna, "os_relative_right", PROP_INT, PROP_UNSIGNED);
+  RNA_def_property_int_sdna(prop, NULL, "onion_skin_cache.relative_right");
+  RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+  RNA_def_property_ui_text(
+      prop, "Onion Skin Range Right", "how far to the lef to draw onion skins");
   RNA_def_property_update(prop, NC_SPACE | ND_SPACE_VIEW3D | NS_VIEW3D_SHADING, NULL);
 
   prop = RNA_def_property(srna, "onion_skin_alpha", PROP_FLOAT, PROP_FACTOR);
-- 
2.30.2


From efa97892e0696907a7064e0a5e562286e332c581 Mon Sep 17 00:00:00 2001
From: Christoph Lendenfeld <chris.lenden@gmail.com>
Date: Fri, 26 May 2023 18:06:29 +0200
Subject: [PATCH 16/16] outline wip

---
 scripts/startup/bl_ui/properties_render.py     |  1 +
 .../draw/engines/overlay/overlay_onion_skin.cc | 18 ++++++++++++++----
 .../draw/engines/overlay/overlay_private.hh    |  2 ++
 .../draw/engines/overlay/overlay_shader.cc     | 11 +++++++++++
 .../shaders/infos/overlay_extra_info.hh        |  1 +
 source/blender/makesdna/DNA_scene_types.h      |  7 ++++++-
 source/blender/makesrna/intern/rna_scene.c     | 12 ++++++++++++
 7 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/scripts/startup/bl_ui/properties_render.py b/scripts/startup/bl_ui/properties_render.py
index 6d9def40e2a..f83ecc7e20f 100644
--- a/scripts/startup/bl_ui/properties_render.py
+++ b/scripts/startup/bl_ui/properties_render.py
@@ -739,6 +739,7 @@ class RENDER_PT_onion_skins(RenderButtonsPanel, Panel):
         col.prop(scene, "os_relative_left")
         col.prop(scene, "os_relative_right")
         col.prop(scene, "onion_skin_alpha")
+        col.prop(scene, "onion_skin_draw_modes")
 
 
 class RENDER_PT_opengl_sampling(RenderButtonsPanel, Panel):
diff --git a/source/blender/draw/engines/overlay/overlay_onion_skin.cc b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
index dd39a726669..a0fbcb3aa26 100644
--- a/source/blender/draw/engines/overlay/overlay_onion_skin.cc
+++ b/source/blender/draw/engines/overlay/overlay_onion_skin.cc
@@ -11,10 +11,14 @@ void OVERLAY_onion_skin_init(OVERLAY_Data *vedata)
   DRWState state = DRW_STATE_WRITE_COLOR | DRW_STATE_BLEND_ALPHA;
   DRW_PASS_CREATE(psl->onion_skin_ps, state | pd->clipping_state);
 
-  GPUShader *shader = OVERLAY_shader_onion_skin_mesh();
   DRWShadingGroup *grp;
-  pd->onion_skin_grp = grp = DRW_shgroup_create(shader, psl->onion_skin_ps);
 
+  GPUShader *shader = OVERLAY_shader_onion_skin_mesh();
+  pd->onion_skin_grp = grp = DRW_shgroup_create(shader, psl->onion_skin_ps);
+  DRW_shgroup_uniform_block(grp, "globalsBlock", G_draw.block_ubo);
+
+  GPUShader *shader_outline = OVERLAY_shader_onion_skin_outline();
+  pd->onion_skin_outline_grp = grp = DRW_shgroup_create(shader_outline, psl->onion_skin_ps);
   DRW_shgroup_uniform_block(grp, "globalsBlock", G_draw.block_ubo);
 }
 
@@ -32,14 +36,20 @@ static bool str_equals(const char *__restrict str, const char *__restrict start)
 void OVERLAY_onion_skin_populate(OVERLAY_Data *vedata, Object *ob)
 {
   OVERLAY_PrivateData *pd = vedata->stl->pd;
-  DRWShadingGroup *grp = pd->onion_skin_grp;
 
   const DRWContextState *draw_ctx = DRW_context_state_get();
 
   Scene *scene = draw_ctx->scene;
   const float current_frame = BKE_scene_ctime_get(scene);
 
-  DRW_shgroup_uniform_float_copy(grp, "alpha", draw_ctx->scene->onion_skin_cache.alpha);
+  DRWShadingGroup *grp = nullptr;
+  if (scene->onion_skin_cache.draw_method == ONION_SKIN_DRAW_SOLID) {
+    grp = pd->onion_skin_grp;
+  }
+  else {
+    grp = pd->onion_skin_outline_grp;
+  }
+  DRW_shgroup_uniform_float_copy(grp, "alpha", scene->onion_skin_cache.alpha);
 
   LISTBASE_FOREACH (OnionSkinMeshLink *, mesh_link, &scene->onion_skin_cache.objects) {
     if (!str_equals(ob->id.name, mesh_link->object->id.name)) {
diff --git a/source/blender/draw/engines/overlay/overlay_private.hh b/source/blender/draw/engines/overlay/overlay_private.hh
index 87a7d72aa92..9893ddeac3a 100644
--- a/source/blender/draw/engines/overlay/overlay_private.hh
+++ b/source/blender/draw/engines/overlay/overlay_private.hh
@@ -281,6 +281,7 @@ typedef struct OVERLAY_PrivateData {
   DRWShadingGroup *motion_path_lines_grp;
   DRWShadingGroup *motion_path_points_grp;
   DRWShadingGroup *onion_skin_grp;
+  DRWShadingGroup *onion_skin_outline_grp;
   DRWShadingGroup *outlines_grp;
   DRWShadingGroup *outlines_curves_grp;
   DRWShadingGroup *outlines_ptcloud_grp;
@@ -777,6 +778,7 @@ GPUShader *OVERLAY_shader_image(void);
 GPUShader *OVERLAY_shader_motion_path_line(void);
 GPUShader *OVERLAY_shader_motion_path_vert(void);
 GPUShader *OVERLAY_shader_onion_skin_mesh(void);
+GPUShader *OVERLAY_shader_onion_skin_outline(void);
 GPUShader *OVERLAY_shader_uniform_color(void);
 GPUShader *OVERLAY_shader_uniform_color_pointcloud(void);
 GPUShader *OVERLAY_shader_outline_prepass(bool use_wire);
diff --git a/source/blender/draw/engines/overlay/overlay_shader.cc b/source/blender/draw/engines/overlay/overlay_shader.cc
index b40499a03b9..52af0f080f3 100644
--- a/source/blender/draw/engines/overlay/overlay_shader.cc
+++ b/source/blender/draw/engines/overlay/overlay_shader.cc
@@ -79,6 +79,7 @@ struct OVERLAY_Shaders {
   GPUShader *motion_path_line;
   GPUShader *motion_path_vert;
   GPUShader *onion_skin_mesh;
+  GPUShader *onion_skin_outline;
   GPUShader *outline_prepass;
   GPUShader *outline_prepass_curves;
   GPUShader *outline_prepass_gpencil;
@@ -696,6 +697,16 @@ GPUShader *OVERLAY_shader_onion_skin_mesh(void)
   return sh_data->onion_skin_mesh;
 }
 
+GPUShader *OVERLAY_shader_onion_skin_outline(void)
+{
+  const DRWContextState *draw_ctx = DRW_context_state_get();
+  OVERLAY_Shaders *sh_data = &e_data.sh_data[draw_ctx->sh_cfg];
+  if (!sh_data->onion_skin_outline) {
+    sh_data->onion_skin_outline = GPU_shader_create_from_info_name("overlay_outline_detect");
+  }
+  return sh_data->onion_skin_outline;
+}
+
 GPUShader *OVERLAY_shader_outline_prepass(bool use_wire)
 {
   const DRWContextState *draw_ctx = DRW_context_state_get();
diff --git a/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh b/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh
index b67736c9bfd..0b817b0f565 100644
--- a/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh
+++ b/source/blender/draw/engines/overlay/shaders/infos/overlay_extra_info.hh
@@ -260,6 +260,7 @@ GPU_SHADER_CREATE_INFO(overlay_onion_skin_mesh)
     .vertex_out(onion_skin_iface)
     .push_constant(Type::VEC3, "color")
     .push_constant(Type::FLOAT, "alpha")
+    .push_constant(Type::INT, "draw_method")
     .fragment_out(0, Type::VEC4, "fragColor")
     .fragment_source("overlay_onion_skin_mesh_frag.glsl")
     .vertex_source("overlay_onion_skin_mesh_vert.glsl")
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 28a835cd580..56f71870ae2 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -1865,12 +1865,17 @@ typedef struct OnionSkinMeshLink {
   char _pad[4];
 } OnionSkinMeshLink;
 
+enum {
+  ONION_SKIN_DRAW_SOLID = 0,
+  ONION_SKIN_DRAW_OUTLINE = 1,
+};
+
 typedef struct SceneOnionSkin {
   float color_left[3];
   float color_right[3];
   float alpha;
   int relative_left, relative_right;
-  char _pad[4];
+  int draw_method;
   ListBase objects /* OnionSkinMeshLink */;
 } SceneOnionSkin;
 
diff --git a/source/blender/makesrna/intern/rna_scene.c b/source/blender/makesrna/intern/rna_scene.c
index b5253ad5395..0091d271ca9 100644
--- a/source/blender/makesrna/intern/rna_scene.c
+++ b/source/blender/makesrna/intern/rna_scene.c
@@ -671,6 +671,12 @@ static const EnumPropertyItem plane_orientation_items[] = {
     {0, NULL, 0, NULL, NULL},
 };
 
+static const EnumPropertyItem onion_skin_draw_modes[] = {
+    {ONION_SKIN_DRAW_SOLID, "SOLID", 0, "Solid", "Draw solid shape"},
+    {ONION_SKIN_DRAW_OUTLINE, "OUTLINE", 0, "Outline", "Draw outline"},
+    {0, NULL, 0, NULL, NULL},
+};
+
 static const EnumPropertyItem snap_to_items[] = {
     {SCE_SNAP_MODE_GEOM, "GEOMETRY", 0, "Geometry", "Snap to all geometry"},
     {SCE_SNAP_MODE_NONE, "DEFAULT", 0, "Default", "Use the current snap settings"},
@@ -8478,6 +8484,12 @@ void RNA_def_scene(BlenderRNA *brna)
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
   RNA_def_property_update(prop, NC_SPACE | ND_SPACE_VIEW3D | NS_VIEW3D_SHADING, NULL);
 
+  prop = RNA_def_property(srna, "onion_skin_draw_modes", PROP_ENUM, PROP_NONE);
+  RNA_def_property_enum_sdna(prop, NULL, "onion_skin_cache.draw_method");
+  RNA_def_property_enum_items(prop, onion_skin_draw_modes);
+  RNA_def_property_enum_default(prop, ONION_SKIN_DRAW_SOLID);
+  RNA_def_property_ui_text(prop, "Onion Skin Draw Modes", "How to draw os's");
+
   /* Nestled Data. */
   /* *** Non-Animated *** */
   RNA_define_animate_sdna(false);
-- 
2.30.2