Alembic\USD: Mesh Sequence Cache data loading and configuration #124554

New Issue

Jesse Yurkovich · 2024-07-11T22:27:26+02:00

Jesse Yurkovich commented

2024-07-11 22:27:26 +02:00

Context

The Mesh Sequence Cache (MSC) modifier allows data from Alembic and USD files to be loaded on a per-frame basis for time-varying mesh and curve data. In order for this to happen properly, the Mesh Sequence Cache needs to be configured with the correct set of flags/options which determines what type of data to read during each frame. These options are used to construct the native Alembic and USD "import options" data structures which ultimately control the actual loading of data.

Existing Tasks and PRs

[1] #104683
[2] #118754

Problem

Currently 5 flags are possible to set on the MSC which determine which data to load as we advance the timeline: Vertex, Faces, UV, Color, and Attribute data

The Attribute flag is "hidden" and not exposed in the UI today (a bug to be handled separately)
New scenarios have come to light which would necessitate adding at least one more option: Material data
In the case of USD, of the 36 total options available during Import, only those corresponding to the 5 existing flags are correctly set when the MSC needs to read a given frame of data. Not all 36 options relate to mesh geometry data, it just serves to put the scale of the problem into perspective.

There may be more cases beyond Materials in the future. The question becomes: Do we just add more options, 1 by 1, as they are found?

A compounding issue is that users are able to add/remove this modifier at will. While it will typically be created automatically during the Import process, the user is free to set things up manually. This means that while it is possible to "attach" the original Import properties in full fidelity to the MSC internally, the user would have no way of doing so on their own or after the fact.

Choices to consider

Continue to add new MSC options in an as-needed fashion as they present themselves.
Associate the actual Import properties with the MSC, in their full form, so that the MSC can always call the Importer with the right set of parameters at a later time.

Being able to associate the actual properties to the MSC is the ideal solution. The main problem is how to enable the user to do so when they add the MSC manually. Assuming we can show the user the all the required properties for USD/Alembic import, we'd then have to store them, and then use them whenever we create the various USD/Alembic readers later on, which may require additional changes.

Decision needed

<which choices to plan and investigate further>

## Context The Mesh Sequence Cache (MSC) modifier allows data from Alembic and USD files to be loaded on a per-frame basis for time-varying mesh and curve data. In order for this to happen properly, the Mesh Sequence Cache needs to be configured with the correct set of flags/options which determines what type of data to read during each frame. These options are used to construct the native Alembic and USD "import options" data structures which ultimately control the actual loading of data. #### Existing Tasks and PRs [1] https://projects.blender.org/blender/blender/pulls/104683 [2] https://projects.blender.org/blender/blender/issues/118754 ## Problem Currently 5 flags are possible to set on the MSC which determine which data to load as we advance the timeline: `Vertex`, `Faces`, `UV`, `Color`, and `Attribute` data - The `Attribute` flag is "hidden" and not exposed in the UI today (a bug to be handled separately) - New scenarios have come to light which would necessitate adding at least one more option: `Material` data - In the case of USD, of the 36 total options available during Import, only those corresponding to the 5 existing flags are correctly set when the MSC needs to read a given frame of data. Not all 36 options relate to mesh geometry data, it just serves to put the scale of the problem into perspective. There may be more cases beyond Materials in the future. The question becomes: Do we just add more options, 1 by 1, as they are found? A compounding issue is that users are able to add/remove this modifier at will. While it will typically be created automatically during the Import process, the user is free to set things up manually. This means that while it is possible to "attach" the original Import properties in full fidelity to the MSC internally, the user would have no way of doing so on their own or after the fact. ## Choices to consider - Continue to add new MSC options in an as-needed fashion as they present themselves. - Associate the actual Import properties with the MSC, in their full form, so that the MSC can always call the Importer with the right set of parameters at a later time. Being able to associate the actual properties to the MSC is the ideal solution. The main problem is how to enable the user to do so when they add the MSC manually. Assuming we can show the user the all the required properties for USD/Alembic import, we'd then have to store them, and then use them whenever we create the various USD/Alembic readers later on, which may require additional changes. ## Decision needed `<which choices to plan and investigate further>`

Jesse Yurkovich added the

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Alembic\USD: Mesh Sequence Cache data loading and configuration #124554

Context

Existing Tasks and PRs

Problem

Choices to consider

Decision needed