Adds ModelExperimental3DTileContent, B3dmLoader, removes Cesium3DTileContentFeatureTable

[sanjeetsuhag]

Overview

This PR introduces a new Cesium3DTileContent class called ModelExperimental3DTileContent. This class is used when ModelExperimental is enabled and is meant to handle all types of 3D Tile content by passing them to the correct loading function (currently only supports .b3dm and .gltf/.glb).

It also adds a new B3dmLoader, which is a light wrapper around the GtlfLoader, but adds some additional functionality:

• parsing feature table
• parsing batch table
• generating feature metadata
• handling feature table semantics

The Cesium3DTileContentFeatureTable and all adjacent code has been removed. Additionally, the Batched3DModel3DTileContent and Gltf3DTileContent classes have been restored to their pre-ModelExperimental states.

Task List:

• Fix states in B3dmLoader
• Remove unused tests in Batched3DModel3DTileContent and Gltf3DTileContent
• Adds tests for B3dmLoader
• Add tests for new functionality in ModelFeatureTable
• Fix tests for existing stages
• Improve documentation
• Add specs for ModelExperimental3DTileContent

Testing

• 3D Tiles Sandcastle

[cesium-concierge]

Thanks for the pull request @sanjeetsuhag!

• ✔️ Signed CLA found.
• ❔ CHANGES.md was not updated.
  • If this change updates the public API in any way, please add a bullet point to CHANGES.md.
• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.

[sanjeetsuhag]

Getting some weird behavior with picking instanced meshes. Looking into it now. Fixed

[ptrgags]

@sanjeetsuhag reviewed the code, a few things need updating. I'll try this out in a Sandcastle next.

[ptrgags]

@sanjeetsuhag as a smoke test, I tried loading the NYC dataset in ModelExperimental with this Sandcastle -- it's not showing up:

It should look like this:

Sandcastle on sandcastle.cesium.com

[sanjeetsuhag]

As suspected, the issue above was due to mishandling of the coordinate transforms. The B3dmLoader was applying the RTC transform directly on the node and ModelExperimentalSceneGraph was adjusting the transforms after that. Instead of having to add a "reverse" matrix multiplication step to account for the transform that will be applied later, I instead added an rtcTransform to the loader itself, and it allows simple multiplication of the modelMatrix (that only needs to happen once, not per-node).

The Sandcastle works as expected now.

[sanjeetsuhag]

@ptrgags I have addressed your feedback.

[ptrgags]

@sanjeetsuhag works correctly now! Though two things:

• looks like B3DMParserSpec is missing
• also check coverage results, I see that ModelExperimental3DTileContent is only at 68% coverage

[ptrgags]

Looks good to me, @lilleyse did you want to take a look before I merge?

[lilleyse]

Overall looks good and simpler than before. I like how tile content is now only accessed in a few places.

[lilleyse]

No comments, look good!