Overlays: Reserve space for a "Onion Skins" overlay

While we probably won't be getting a general purpose "Onion Skinning"
overlay anytime soon for meshes, etc. (at least not before the
depsgraph stabilises, and we also get geometry caching working),
for the Grease Pencil integration at least, it makes sense to move
GP objects to using a more general/future-proof solution, instead
of continuing to use a special/dedicated button in the header.

Currently the UI part of this is commented out. Also, the GP branch
doesn't need to move to this pre-merge. But, since 2.8 changes move
fast, it's better to reserve the space now to have it next to motionpaths,
than introduce it later.

2 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/makesdna/DNA_view3d_types.h b/source/blender/makesdna/DNA_view3d_types.h
index 9794a1efbf5..9686981d674 100644
--- a/source/blender/makesdna/DNA_view3d_types.h
+++ b/source/blender/makesdna/DNA_view3d_types.h
@@ -371,6 +371,7 @@ enum {
 	V3D_OVERLAY_WIREFRAMES        = (1 << 4),
 	V3D_OVERLAY_HIDE_TEXT         = (1 << 5),
 	V3D_OVERLAY_HIDE_MOTION_PATHS = (1 << 6),
+	V3D_OVERLAY_ONION_SKINS       = (1 << 7),
 };
 
 /* View3DOverlay->edit_flag */
diff --git a/source/blender/makesrna/intern/rna_space.c b/source/blender/makesrna/intern/rna_space.c
index 489f2b73bf3..fca8e3ab9f9 100644
--- a/source/blender/makesrna/intern/rna_space.c
+++ b/source/blender/makesrna/intern/rna_space.c
@@ -2583,6 +2583,12 @@ static void rna_def_space_view3d_overlay(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Motion Paths", "Show the Motion Paths Overlay");
 	RNA_def_property_update(prop, NC_SPACE | ND_SPACE_VIEW3D, NULL);
 
+	prop = RNA_def_property(srna, "show_onion_skins", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "overlay.flag", V3D_OVERLAY_ONION_SKINS);
+	RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+	RNA_def_property_ui_text(prop, "Onion Skins", "Show the Onion Skinning Overlay");
+	RNA_def_property_update(prop, NC_SPACE | ND_SPACE_VIEW3D, NULL);
+
 	prop = RNA_def_property(srna, "show_look_dev", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_sdna(prop, NULL, "overlay.flag", V3D_OVERLAY_LOOK_DEV);
 	RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);