Overlay: Fade Inactive Geometry

This implements a new overlay that blends the bakground color over the
objects that are not in the same mode as the active object, making
them fade with the background.
This is especially needed for sculpt mode as there is no other overlay
or indication in the viewport to display which object is active.

This is intended to be used with D7510 in order to have a faster
workflow when sculpting models with multiple objects.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D8679

release/scripts/startup/bl_ui/space_view3d.py

@@ -6122,6 +6122,10 @@ class VIEW3D_PT_overlay_geometry(Panel):
         col.active = display_all
 
         col.prop(overlay, "show_face_orientation")
+        row = col.row(align=True)
+        row.prop(overlay, "show_fade_inactive", text="")
+        sub = row.row()
+        sub.prop(overlay, "fade_inactive_alpha", text="Fade Inactive Geometry")
 
         # sub.prop(overlay, "show_onion_skins")