Fix T88026: Repeated switch to rendered viewport crashes

Resolve ownership ambiguity with shared physics pointers.

Previously, LIB_ID_CREATE_NO_MAIN allowed pointer sharing with
the source ID so physics caches can be shared between original and
evaluated data: (Object.soft.shared & Object.rigidbody_object.shared).

This only worked properly for LIB_TAG_COPIED_ON_WRITE ID's,
as LIB_TAG_NO_MAIN can be used in situations where the original ID's
lifetime limited by it's original data.

This commit adds `LIB_ID_COPY_SET_COPIED_ON_WRITE` so ID's only share
memory with original data for ID's evaluated in the depsgraph.

For all other uses, a full copy of physics data is made.

Ref D11228#287094

1 files changed, 8 insertions, 1 deletions

diff --git a/source/blender/makesdna/DNA_ID.h b/source/blender/makesdna/DNA_ID.h
index fa60bba54d5..8bf9afafa1b 100644
--- a/source/blender/makesdna/DNA_ID.h
+++ b/source/blender/makesdna/DNA_ID.h
@@ -555,8 +555,15 @@ enum {
   /* RESET_AFTER_USE tag existing data before linking so we know what is new. */
   LIB_TAG_PRE_EXISTING = 1 << 11,
 
-  /* The data-block is a copy-on-write/localized version. */
+  /**
+   * The data-block is a copy-on-write/localized version.
+   *
+   * \warning This should not be cleared on existing data.
+   * If support for this is needed, see T88026 as this flag controls memory ownership
+   * of physics *shared* pointers.
+   */
   LIB_TAG_COPIED_ON_WRITE = 1 << 12,
+
   LIB_TAG_COPIED_ON_WRITE_EVAL_RESULT = 1 << 13,
   LIB_TAG_LOCALIZED = 1 << 14,