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):

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)) {

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);

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();

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")

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;
 

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);