Getting Started

‍INFO Currently, we only support specific set of DCCs and their versions, and AyonUsd for building revolvers (other software packages and stand-alone setups will follow).

Welcome to the Developer Docs. This document will be split into 2 portions.

1: the Resolver Developer part. Lets take a look at what tools and library's we use and how we use them.

2: documentation for AYON developers that want to use the resolver but don't want to work on the source code. it will outline all the things the resolver offers and how you can control them.

Resolver Developers

Dependencies

• AyonCppApi
  Internal AyonCppApi. Used for communication with the server and specifically designed to allow for Fast resolution.
• HttpLib
  Header only Http lib that we use in the Cpp api to communicate with the server.
• USD
  OpenUsd library from Pixar

compilation

The build.py script located in the scripts folder serves as our primary build script, superseding the previous .sh and .bat files. We plan to replace this with 'Build Stage' using Ayon Automator in the future.

Target tools for compilation are organized into separate BuildPlugins. To compile for a specific tool, select the corresponding BuildPlugin and provide the required environment variables for that tool. Subsequently, execute build.py, ensuring you specify the chosen BuildPlugin as an environment variable.

Varlibes:

COMPILEPLUGIN = Set this variable to the relative path of the desired build plugin, found within the BuildPlugins folder in the repository root. For example, if using HouLinux/LinuxPy310Houdini20.

Developer Guidelines

Testing

The USD Resolver currently does not employ Red-Green development. However, post-alpha release, we plan to integrate Ayon Automator.

Issue Tracking We maintain all our work in GitHub (GH) issues and create branches from these issues. Here are the three types of issue options:

• Bug Report: For reporting any bugs or glitches.
• Feature Request: For suggesting new features or improvements.
• Proposal: For significant changes or complex feature implementations, allowing discussion on technical approaches and review of past decisions.

Choose your Issue Type Depending on the scale of work, you can pick the issue type that best fits. However, for substantial features with high complexity, it's crucial to create a Proposal. This ensures thoughtful debate around technical implementation and allows us to revisit older proposals for context.

Working with Build Plugins

Naming Build Plugins

Build Plugins Naming schema is as follows: {AppName}{PlatfromName}/{AppName}{AppVersion}_Py{pythonVersion}_{PlatfromName}.cmake PlatformName options = {Win, Linux, Mac, specific Os Name}

Resolver Internals

Resolver Behavior:

On USD Init:

• AyonUsdResolver library will be loaded, and a resolverContextCache and a globally accessible shared_ptr will be created

When a USD file is opened:

• Resolver Context is created.
  • every resolver context has a shared_ptr that will point to the global resolverContextCache

When a USD AssetIdentifier is found.

• _Resolve() gets called with the data between the '@' symbols.
• _Resolve() checks if the path is an AYON URI path.
  • Yes? Then we get the current context (because in this resolver, the resolver context interacts with the AyonCppApi and not the Resolver).
    • We ask the ResolverContext to return the path to us, and the ResolverContext calls the getAsset() function in the resolverContextCache.
    • The resolverContextCache will then first check the PreCache and then the Responsible cache. If the resolverContextCache finds the asset, it will return a assetIdent. If the resolverContextCache does not find an asset, it will call the AyonCppApi and request the asset information from the server.
  • No? Then we check if the AssetIdentifier was already registered in the CommonCache, and if so, we will return the cached entry. If not, we will resolve the path against the operating file system the same way that USD Default Resolver does it.

Asset Identifier Behavior:

The AssetIdentifier or AssetPath converts an AYON path to a disk path for the resolver:

1. ayon: signifies an AYON asset (detected via string view comparison).
2. //{ProjectName}/{path/to/ayon/folder}?product={FileName} defines the desired Ayon folder.
3. Version options:
   • latest: Uses latest version available.
   • hero: Searches for pinned hero version, if configured.
   • Specific version number (e.g., v001): Uses specified product version.

The complete asset path format is: ayon://{ProjectName}/{path/to/ayon/folder}?product={FileName}&version=latest&representation=usd

‍CPP files may contain TF_DEBUG().Msg(); and one of the enum values (AYONUSDRESOLVER_RESOLVER, AYONUSDRESOLVER_RESOLVER_CONTEXT). These control debug message output. Keep these in your environment variables for flexibility.

Ayon Developers

Pythonic Usage via USD

First of all, if you setup the resolver via the AyonUsd addon usd will automatically use it as the default resolver meaning every time you call a resolver AyonUsdResolver will be used.

But you have more fine grained control if you want to:

from pxr import Ar
from usdAssetResolver import AyonUsdResolver
Ar.SetPreferredResolver("AyonUsdResolver")

‍note When you get a resolver via Usd.Ar API you will need to get an explicit context to edit the global context as Ar.GetResolver will return a higher order class and not AyonUsdResolver class.

resolver = Ar.GetResolver()
context = AyonUsdResolver.ResolverContext()

If you want fine control over the resolver you will be able to get the connected context via GetConnectedContext
tip Dropping cache entries Using the resolver.GetConnectedContext() is also the recommended way to access the dropCache function for the resolver.

explicit_resolver = AyonUsdResolver.Resolver()
explicit_resolver_context = explicit_resolver.GetConnectedContext()

To access the Python bindings for the AyonUsdResolver:

from usdAssetResolver import AyonUsdResolver

Ar.SetPreferredResolver("AyonUsdResolver") this command allows you to set a preferred Resolver. If you use the AyonUsd addon you wont need to set this line as we register the resolver as the main resolver. But if you have a different resolver set as Main you might need to use this command.

resolver = Ar.GetResolver() there are multiple ways to get access to a resolver instance but using the "Default" Usd option is usually the best idea as it will return the resolver for the current context.

context = AyonUsdResolver.ResolverContext() accessing an ResolverContext instance is useful if you want to manipulate the Global resolver cache.

Pinning

the AyonUsdResolver has a feature called Pinning Support.
In short pinning support allows you to load a pinning file and disconnect the AyonCppApi.
In the implementation this boils down to a static Memory cache that bypasses the resolver Logic.

‍note Why use pinning? When running a resolver on a farm with many workers (render nodes) you might not want them all to call the Ayon server to avoid impacting the server performance. This is because USD Resolvers will resolve paths one by one, potentially resulting in many calls.

How to use it ?
There are 3 Env variables that control the Pinning file support

ENABLE_STATIC_GLOBAL_CACHE
Enables or Disables static Cache creation. This effectively allows you to enable or disable Pinning file support.
as you might want to have a pinning file in your env vars but for e.g debugging you don't want to activate the feature.

PINNING_FILE_PATH
This is a path to the pinning file.

PROJECT_ROOTS
When running the resolver against the AYON server the CppApi will query the Get Project Site Roots endpoint and get a Dict[str,str] of {root[RootOverwriteKey]}=Val overwrites.
when running with a pinning file you will need to set this Dict[str,str] as an ENV variable. e.g:{Key}:{Path},{Key}:{Path} it's not a problem to have duplicates in the keys but the Cache stores the data as an Unordered_Map so it will end up deduplicating the Keys. But you can't have spaces in the list as they are not removed and will be interpreted as part of the Key or Value.

example
setup the resolver for pinning support. we empty all the AYON c++ api keys just for example you can simply not set them.

export AYON_API_KEY=""
export AYON_SITE_ID=""
export AYON_SERVER_URL=""
export AYON_PROJECT_NAME=""
 
export AYONLOGGERLOGLVL=""
export AYONLOGGERFILELOGGING=""
export AYONLOGGERFILEPOS=""
 
export ENABLE_STATIC_GLOBAL_CACHE="true"
export PINNING_FILE_PATH="/path/to/pinning.json"
export PROJECT_ROOTS="key:/val,key:/val"
 
export TF_DEBUG=""

stage = Usd.Stage.Open(pinning_file_json["ayon_pinning_data_entry_sceene"])
print(stage.ExportToString())

PS: its interesting to know that when you generate a pinning file via the AYON-USD addon the json file will have a key named

ayon_pinning_data_entry_scene.
This should always be the path used to open the stage Otherwise the pinning file might not have the correct AssetIdentifier stored.
aka: if this key points to a local path and you use an URI that points to the local path the resolver wont be able to resolve.

Controlling the cache

context = AyonUsdResolver.ResolverContext() there are multiple ways to control the cache of a resolver. but if your resolver uses the global cache you can simply create a new ResolverContext and access the cache control functions to

affect the global cache.
This does not work if you disconnected the Global cache from your resolver.

context.deleteFromCache(AssetIdentifier) delete an individual cached entry. context.clearCache() clear the connected cache.

‍note It is important to understand that by default a Resolver will be connected to the global cache and this call will delete all entries in the global cache not just the ones that where added by this resolver.

context.dropCache() allows you do disconnect from the current cache object and initialize a new one. This can be useful if you want to disconnect from the global cache and have a Resolver local cache instead.

explicit_resolver = AyonUsdResolver.Resolver() if you need to create an explicit resolver because you want to e.g pass a specific instance into a stage or you want to disconnect from the Global Cache you should access the Context

connected to this specific resolver.
explicit_resolver_context = explicit_resolver.GetConnectedContext() all the other functions stay the same.

Examples

Deleting cached entry's

resolver = Ar.GetResolver()
context = AyonUsdResolver.ResolverContext()
 
# Delete From the Global Cache
asset_identifier: str="ayon://{ProjectName}/{path/to/ayon/folder}?product={FileName}&version=latest&representation=usd"
context.deleteFromCache(asset_identifier)
 
# Clear the Global Cache
context.clearCache()

Disconnecting from the global cache

explicit_resolver = AyonUsdResolver.Resolver()
explicit_resolver_context = explicit_resolver.GetConnectedContext()
 
# Drooping the cache so that the resolver will generate its own dedicated cache instance
explicit_resolver_context.dropCache()
 
# Delete from cache and clearCache will also work with an explicit_resolver_context