ID: Sanitize handling of 'USER_ONE' (ensure_user) case.

Note that this has little impact on current master - yet it allows to fix the 'Image Editor' bug
(open image in editor, use same image in texture, delete image from texture, image us is 0 and
red in image editor...) and probably a few other similar cases.

But that change is mandatory to get a proper handling of ID deletion/reamapping/reloading/etc. as done in id-remap branch.

Instead of just adding a user if none already present, new code use two new ID tags to get a three-states status:
  - Normal: nothing changes.
  - Needs extra user: we know that ID needs an extra user, so we take of never going down to 0 in 'real' usercount handling.
  - Has extra user: we do have increased that ID usercount to get our needed extrauser.

Reviewers: sergey, campbellbarton

Differential Revision: https://developer.blender.org/D1696

1 files changed, 5 insertions, 0 deletions

diff --git a/source/blender/makesdna/DNA_ID.h b/source/blender/makesdna/DNA_ID.h
index 74a63be8bbc..0bf3c350263 100644
--- a/source/blender/makesdna/DNA_ID.h
+++ b/source/blender/makesdna/DNA_ID.h
@@ -313,6 +313,11 @@ enum {
 	/* RESET_NEVER tag datablock as a place-holder (because the real one could not be linked from its library e.g.). */
 	LIB_TAG_MISSING         = 1 << 6,
 
+	/* tag datablock has having an extra user. */
+	LIB_TAG_EXTRAUSER       = 1 << 2,
+	/* tag datablock has having actually increased usercount for the extra virtual user. */
+	LIB_TAG_EXTRAUSER_SET   = 1 << 7,
+
 	/* RESET_AFTER_USE tag newly duplicated/copied IDs. */
 	LIB_TAG_NEW             = 1 << 8,
 	/* RESET_BEFORE_USE free test flag.