Introduction​

AYON Loader HDAs serve as controllers that let you select and load AYON products into your scene.

• Generic Loader: As the name suggests, it is generic and loads any AYON product as a filepath.

• Lop Import (Load Asset): Loads USD assets.

• Load Shot: Loads USD shots.

Generic Loader

Currently, Available in OBJs, SOPs and LOPs.

LOP Import	Load Shot

Access Loader HDAs​

TAB Menu​

These nodes are accessible in the TAB menu.

LOPs	OBJs	SOPs

Loader Tool​

Some loader plugins rely on these nodes to perform loading:

1. Load Asset: Creates a LOP Import node in \stage.

2. Load Shot: Creates a Load Shot node in \stage.

3. Load Filepath to Node: Creates a Generic Loader node in \obj\AVALON_CONTAINERS.

Quickly Load into Any String Parameter​

You can find a parameter action called Load with AYON by right-clicking any file-type parameter on non-Rop nodes. This action creates a Generic Loader node in \obj\AVALON_CONTAINERS, copies its file parameter to the File parameter where the action was triggered, and opens the parameter panel for the created Generic Loader node.

Loader HDAs​

Generic Loader​

Overview​

Parameters​

• Project: Select a project.

• Folder Path: Select a folder path.

• Folder Name: Shows the name of the selected folder.

• Product: Select a product.

• Version: Select the product's version.

• Representation: Select the product's representation (format).

• Enable Representation Filter: Toggle to show the Representation Filter parameter.

• Representation Filter: Enter a space-separated list of representation names to filter. This filters the representation drop-down menu.

• Clear Cache: Clears the node's cache.

• File: Displays the file of the selected product. Automatically applies $F and <UDIM> tokens.

• Use AYON Entity URI: When enabled, the File parameter becomes an AYON URI.

• Show Entity Thumbnail: When enabled, shows the selected product's thumbnail and extra parameters for adjusting the image in the network view.

• Size & Offset: Adjust the displayed thumbnail in the network view.

• Update Thumbnail: Click to manually update the thumbnail. Use this if auto-update doesn't work.

• Show Pipeline Parms: Displays extra pipeline parameters like Representation ID, mainly for debugging and automation.

• Nodes Referencing File: Displays nodes that reference the File parameter.

How to Use Generic Loader​

1. Select the project and folder path.

2. Choose the product, version, and representation.

3. The File parameter will be populated, allowing you to copy and use it as needed.

4. Product selection fields support expressions and context options. Find examples below Example Usages.

Lop Import​

Overview​

It uses a combination of the Generic Loader and the Reference node.

The representation filter parameter on the inner Generic Loader node is set to:

usd usda usdlc usdnc abc

Parameters​

This shares the same parameters as the Generic Loader and adds a few more. It also exposes some parameters of the Reference node.

Additional parameters on the node include:

• Reload Files: Click to reload the contents of all files imported by this node.

• Primitive Root: The referenced prim will be overlayed onto this prim, and the referenced prim’s descendants will become this prim’s descendants. If this prim doesn’t exist, the node will create it.

• Presets: This menu provides default values for building assets and shots.

• Reference Type: The type of composition arc to create to the referenced prim.

• Make Instanceable: Mark the new or modified prims as instanceable.

• Reference Primitive: Controls which prim to import from the multi-input connections.

• Reference Primitive Path: The scene graph path of the prim in the referenced layer that that is composed onto the stage. Contents of the referenced layer outside of this referenced primitive path will not appear on the composed stage. This parameter is only used if the Reference primitive parameter is set to “Reference specific primitive”.

• Time Offset (in Frames): Offsets all time samples from the file or target primitive on the first input. You can use this to re-time animations in the references file.

• Time Scale: Scales all time samples from the file or target primitive on the first input. You can use this to re-time animations in the references file.

How to Use LOP Import​

• Selecting products works the same as with the Generic Loader.

• Set the Primitive Root. The Presets menu provides default values for building assets and shots.

Load Shot​

Overview​

It uses a combination of the Generic Loader and the Sublayer node.

The representation filter parameter on the inner Generic Loader node is set to:

usd usda usdlc usdnc abc

Parameters​

It shares the same parameters as the Generic Loader and also exposes some parameters of the Sublayer node:

• Reload Files: Click to reload the contents of all files imported by this node.

• Mute Layer: Load the layer but immediately mute it. This may be useful if the layer must be loaded for other layers to work, but you don’t need to edit or display it.

• Time Offset (in Frames): Offsets all time samples from the file or target primitive on the first input. You can use this to re-time animations in the references file.

• Time Scale: Scales all time samples from the file or target primitive on the first input. You can use this to re-time animations in the references file.

How to Use Load Shot​

• Selecting products works the same as with the Generic Loader.

• Keep in mind, it adds the loaded product as a sublayer.

Example Usages​ of Loader HDAs

These examples come from tests during the development of the HDAs and various discussions in our community. You might find some inspiration here. While they may not perfectly meet your studio's needs, they can serve as a good starting point.

Context Options and MultiShots​

You can use a context options entry to select from, allowing the user to choose any folder in the project. For example, you can create a context options menu that includes all folder paths in the current project.

Expressions and Context Options​

AYON Loader HDAs support expressions and context options, allowing users to automate operations.

For instance, you can use this feature to load multiple products in a loop with a single loader. This method requires the products to share the same name, differing only by a number.

First, I published three products: pointcacherock_1, pointcacherock_2, and pointcacherock_3.

Next, I loaded them into my scene using loader HDAs in a loop with expressions.

• LOP, expressions, and context options:

  pointcacherock_`@ITERATIONVALUE+1`

  

• SOP, expressions, and detail attribute:

  pointcacherock_`detail("../foreach_count","iteration", 0)+1`

  

Building Custom HDAs on Top of Loader HDAs

Loader HDAs are highly versatile and can be integrated as foundation for building custom Loader HDAs. This guide outlines the process and provides examples to help you get started.

Building a Custom HDA in AYON with a Loader HDA Inside

Follow these steps to create a custom HDA using Houdini AYON loader HDAs and promote the parameters properly:

• Create a Subnetwork: Start by creating a subnetwork.

• Add Internal Nodes: Add the nodes you need within the subnetwork based on your requirements.

• Promote Parameters: Open the Edit Parameter Interface for the subnetwork. In the Parameters tab, go to Node Properties, select the required parameters, and use the arrow button to add them.

  

• Create the HDA: Select your subnetwork, and using the Creator / Publisher

  AYON tool, choose the HDA product type and click Create.

  

• Publish: Publish your HDA to AYON.

  

Extend LOP Loaders Example

This example demonstrates how to extend a LOP import node. The custom HDA allows you to set variants, apply transformations, and perform simple grafting for repositioning the loaded asset in the scene.

Download Example

Expr_load_lop_load_lop_Extended_v004.hda

19.6 KB

Internal Nodes Used:

• lop import

• set variants

• transform

• graft branches

To promote parameters, follow the steps outlined in the previous section.

Promoting Strings with Menus in Multiparms

When promoting strings with menus within a multiparm (e.g., promoting "set variants" parameters), the menu options might not be promoted correctly. Use the following Python snippet for the menu script of that parameter:

Example
Python
Copy
pname = kwargs['parm'].name()
# You only need to specify the name of the inner node.
vsetnode = kwargs['node'].node("setvariants")
menu = []
mitems = vsetnode.parm(pname).menuItems()
mlabels = vsetnode.parm(pname).menuLabels()

for i,item in enumerate(mitems):
    menu.append(item)
    menu.append(mlabels[i])

return(menu)

Texture Pack Loader Example

The texture pack hda example demonstrates creating a custom HDA based on the generic loader. where some parameters of the generic loader were exposed like: project , folder path and version. Other parameters are specific to the custom HDA's logic.

Keep in mind it’s an example for creating your custom HDAs, you can use it as it is in your pipeline or prerferably, you use it as inspiration.

This HDA allows you to load texture bundles into your Houdini scene as a MaterialX material.

This HDA example expects published textures with unified naming conventions in your library project, such as:

• Folder path: e.g. /texturepacks/{texture_pack_name}

• Published Texture Naming: {product_name_prefix}{texture_pack_name}_{map}.
  The product name prefix in my example, it’s image.

  Textures in my screenshot above were published via Working with AYON Tray Publisher with the product type image , variant name TexturePackName_Map , and jpg representation.

  

  The texture pack used in this example is Concrete Floor Poured | Poliigon.

• Map names are hardcoded based on the inner generic loader node names.

  • BaseColor

  • Metallic

  • Normal

  • Roughness

Download example

Expr_texture_pack_loader_texture_pack_loader_Main_v002.hda

17.6 KB