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, 27 insertions, 2 deletions

diff --git a/source/blender/blenkernel/intern/library.c b/source/blender/blenkernel/intern/library.c
index 4403949274a..9e8d48531d7 100644
--- a/source/blender/blenkernel/intern/library.c
+++ b/source/blender/blenkernel/intern/library.c
@@ -162,20 +162,38 @@ void id_lib_extern(ID *id)
 }
 
 /* ensure we have a real user */
+/* Note: Now that we have flags, we could get rid of the 'fake_user' special case, flags are enough to ensure
+ *       we always have a real user.
+ *       However, ID_REAL_USERS is used in several places outside of core library.c, so think we can wait later
+ *       to make this change... */
 void id_us_ensure_real(ID *id)
 {
 	if (id) {
 		const int limit = ID_FAKE_USERS(id);
+		id->tag |= LIB_TAG_EXTRAUSER;
 		if (id->us <= limit) {
-			if (id->us < limit) {
+			if (id->us < limit || ((id->us == limit) && (id->tag & LIB_TAG_EXTRAUSER_SET))) {
 				printf("ID user count error: %s (from '%s')\n", id->name, id->lib ? id->lib->filepath : "[Main]");
 				BLI_assert(0);
 			}
 			id->us = limit + 1;
+			id->tag |= LIB_TAG_EXTRAUSER_SET;
 		}
 	}
 }
 
+/* Unused currently... */
+static void UNUSED_FUNCTION(id_us_clear_real)(ID *id)
+{
+	if (id && (id->tag & LIB_TAG_EXTRAUSER)) {
+		if (id->tag & LIB_TAG_EXTRAUSER_SET) {
+			id->us--;
+			BLI_assert(id->us >= ID_FAKE_USERS(id));
+		}
+		id->tag &= ~(LIB_TAG_EXTRAUSER | LIB_TAG_EXTRAUSER_SET);
+	}
+}
+
 void id_us_plus(ID *id)
 {
 	if (id) {
@@ -190,8 +208,15 @@ void id_us_min(ID *id)
 {
 	if (id) {
 		const int limit = ID_FAKE_USERS(id);
+
+		if ((id->us == limit) && (id->tag & LIB_TAG_EXTRAUSER) && !(id->tag & LIB_TAG_EXTRAUSER_SET)) {
+			/* We need an extra user here, but never actually incremented user count for it so far, do it now. */
+			id_us_ensure_real(id);
+		}
+
 		if (id->us <= limit) {
-			printf("ID user decrement error: %s (from '%s')\n", id->name, id->lib ? id->lib->filepath : "[Main]");
+			printf("ID user decrement error: %s (from '%s'): %d <= %d\n",
+			       id->name, id->lib ? id->lib->filepath : "[Main]", id->us, limit);
 			/* We cannot assert here, because of how we 'delete' datablocks currently (setting their usercount to zero),
 			 * this is weak but it's how it works for now. */
 			/* BLI_assert(0); */