Replace Gltf3DTileContent with ModelExperimental3DTileContent

[j9liu]

Fixes #10049.

In this PR, all instances of Gltf3DTileContent have been replaced by instances of ModelExperimental3DTileContent. The corresponding specs were removed. Additionally, missing tests were added for the glb file format, and the 3D Tiles Next sandcastles were updated to no longer require the enableModelExperimental flag.

Implementing these changes causes three unit tests to fail:

Two of these failures are expected and will be addressed in a later issue. However, the color style test should be working, and @ptrgags mentioned he would look into this tomorrow.

[cesium-concierge]

Thanks for the pull request @j9liu!

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Reviewers, don't forget to make sure that:

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

[j9liu]

@ptrgags - Following up on your suggestion about the color style test, specifying the time doesn't fix the test failure.

If you want to replicate my test, I put this at the beginning of expectColorStyle and changed all instances of expect(scene) in the function to expect(renderOptions).

      const renderOptions = {
        scene: scene,
        time: new JulianDate(2457522.154792),
      };

[ptrgags]

@j9liu okay, I'll take a look at this later today

[ptrgags]

@j9liu this code is looking solid and the sandcastles are working fine.

Just a couple small things aside from that one test that's breaking (which I'll investigate more later today)

[j9liu]

@ptrgags -- thanks for the feedback! Just implemented your changes, so all that's left is figuring out what's wrong with that last test.

[ptrgags]

@j9liu I made a simpler sandcastle to see what's happening with the style. And it's not handling the alpha correctly.

I'm going to investigate more today, There's a chance I could have introduced a regression in #10018, or the model coloring code isn't discarding when it finds alpha = 0

[ptrgags]

@j9liu I confirmed that the model color stage is where the problem is. Though the fix shouldn't happen in the shader, it should be the render state that's updated. I looked back at Model.js and when the model color is invisible (alpha === 0) it updates the render state to skip rendering color and depth (because that would just be wasted GPU cycles)

In Scene/ModelExperimental/ModelColorPipelineStage.js, in the code that checks the alpha, you'll want to add these lines:

const renderStateOptions = renderResources.renderStateOptions;
  if (color.alpha === 0.0) {
    // When the model is invisible disable color and depth writes but still write into the stencil buffer
    renderStateOptions.colorMask = {
      red: false,
      green: false,
      blue: false,
      alpha: false,
    };
    renderStateOptions.depthMask = false;
  } 

However, renderStateOptions right now only exists in PrimitiveRenderResources, so there's a few other small changes needed here:

• ModelRenderResources - initialize renderStateOptions to an empty object
• NodeRenderResources - initialize renderStateOptions to clone from modelRenderResources.renderStateOptions (see other examples in the same file)
• PrimitiveRenderResources - instead of cloning, use combine() to combine the additional properties with nodeRenderResources.renderStateOptions

And update unit tests as necessary.

[j9liu]

@ptrgags - Thanks for the guidance. I added your changes and the test passes now. Let me know if there are any concerns with the code I added.

[ptrgags]

@j9liu this is looking very close, just a few small tweaks before I merge it

[j9liu]

@ptrgags - just pushed!

[ptrgags]

@j9liu changes look good, I'm merging!