It would run into using the same frame twice, looking like "freeze
frames"
Apparently we had a similar issue before, see 3f8ec963e3
Just a PoC to show that this looks like a precision/rounding issue when
getting a "working" `UsdTimeCode`.
In the modifier code, we are doing a roundtrip going from frame >> time
(in seconds -- via `BKE_cachefile_time_offset`) and then back to frame
before we store that in `USDMeshReadParams`.
To avoid the precision loss, this PR introduces
`BKE_cachefile_frame_offset` to stay in the "frame" domain and
circumvent going through FPS alltogether.
There might be better ways to let USD handle the "sightly off"
`UsdTimeCode` better though.
Pull Request: https://projects.blender.org/blender/blender/pulls/139793
- ImBuf reference counting: turn that into just an atomic integer
- Cachefile safety: turn into a mutex, since work under the spinlock
was quite heavy (hashtable creation, other memory allocations)
- Movie clip editor: turn into a mutex, since work under the spinlock
was very heavy (reading files from disk, etc.)
- Mesh intersect: remove the previously commented out spinlock path;
replace BLI mutex with C++ mutex for shorter code
Pull Request: https://projects.blender.org/blender/blender/pulls/137989
