Since the introduction of storage buffers in Blender, the calling
code has been responsible for ensuring the buffer meets allocation
requirements. All backends require the allocation size to be divisible
by 16 bytes. Until now, this was sufficient, but with GPU subdivision
changes, an external library must also adhere to these requirements.
For OpenSubdiv (OSD), some buffers are not 16-byte aligned, leading
to potential misallocation. Currently, this is mitigated by allocating
a few extra bytes, but this approach has the drawback of potentially
reading unintended bytes beyond the source buffer.
This PR adopts a similar approach to vertex buffers: the backend handles
extra byte allocation while ensuring data uploads and downloads function
correctly without requiring those additional bytes.
No changes were needed for Metal, as its allocation size is already
aligned to 256 bytes.
**Alternative solutions considered**:
- Copying the CPU buffer to a larger buffer when needed (performance impact).
- Modifying OSD buffers to allocate extra space (requires changes to an external library).
- Implementing GPU_storagebuf_update_sub.
Ref #135873
Pull Request: https://projects.blender.org/blender/blender/pulls/135716
15d88e544a