63 lines
3.4 KiB
Markdown
63 lines
3.4 KiB
Markdown
Blender Cloud addon
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===================
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Installation requires the [Pillar SDK](https://github.com/armadillica/pillar-python-sdk)
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to be installed. It can either be installed regularly somewhere on
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the Python PATH, or be stored as a [wheel file](http://pythonwheels.com/)
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at `blender_cloud/wheels/pillar_sdk-*.whl`.
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Communication & File Structure
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------------------------------
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### Assumptions
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* Cache is user-global, stored in an OS-specific location, and can be removed/recreated. This
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document refers to that location as `$CACHE`, and is typically a directory like
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`$HOME/.cache/blender/blender_cloud`. Also see
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[T47684](https://developer.blender.org/T47684). This directory should not be tied to the
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version of Blender -- malformed/invalid caches should just be ignored or removed.
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* At the moment, versioning of files is limited to re-syncing to get the latest versions. More
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extensive versioning falls under the umbrella of "asset management" and is out of scope of
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this addon.
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* Users can download texture nodes. Such a download may result in multiple files on the local
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filesystem (think of one texture node containing diffuse, bump and specular maps).
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### Caching
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Caching is performed at different levels:
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* Caching of HTTP GET requests is performed by [CacheControl](https://cachecontrol.readthedocs.org/).
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* Cache is stored in `$CACHE/blender_cloud_http/`; by using the file
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backend, we ensure cache persistence across Blender runs. This
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does require the `lockfile` package to be installed or bundled.
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* The code should be made cache-aware and use the Requests-Cache `CachedSession` sessions.
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This allows for more granular control over where in the code cache is (not) used.
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* Downloaded thumbnails are cached (by us) in `$CACHE/thumbnails/node_uuid/filename`.
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* Use a non-cached HTTP GET to download these (using [session.cache_disabled()](http://requests-cache.readthedocs.org/en/stable/api.html#requests_cache.core.CachedSession.cache_disabled)).
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* HTTP headers are stored as JSON key/value pairs in `$CACHE/thumbnails/node_uuid/filename.headers`.
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* Use the ETag and If-Modified-Since headers to prevent unnecessary re-downloading.
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* Check Content-Length header against actual file size to detect partially-downloaded files that need re-downloading.
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* Downloaded files (such as textures) are handled in the same way as thumbnails (described above),
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but have their metadata stored somewhere else (described below).
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### Filesystem Layout
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* Top-level texture directory, referred to as `$TEXTURES` in this document, can be configured per
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Blender scene. It defaults to a global addon preference, which in turns defaults to `//textures`.
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* Texture files are stored in `$TEXTURES/{project_name}/{node_name}/{node_name}/.../{file_variant}-{file_name}`.
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`file_variant` is "col" for colour/diffuse textures, "nor" for normal/bump textures, etc.
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* Metadata is stored in `$TEXTURES/.blender_cloud`, with the following subdirectories:
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* `projects/{project_uuid}.json` containing the project document from Pillar
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* `nodes/{node_uuid}.json` containing the node document from Pillar
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* `files/{file_uuid}.json` containing the file document from Pillar
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* `index.sqlite` containing a mapping from `{project_name}/{node_name}/{node_name}/...`
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to the UUID of the last-named path component (project, node, or file). This allows us
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to map the path of a filesystem path to its Pillar document.
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