Add debug wireframe to ModelExperimental

[j9liu]

Closes #9066. This PR adds the debugWireframe option to ModelExperimental. The current wireframe code in Model leads to tangled / incorrect wireframes, but ModelExperimental implements it properly.

Model	`Model Experimental

Here's a modified version of the Model Experimental sandcastle that allows you to toggle the wireframe.

This should also work for tilesets with Cesium.ExperimentalFeatures.enableModelExperimental = true. For example, here's the result of the changes in the 3D Tiles Inspector sandcastle (localhost)

With Model	With ModelExperimental

Note: this required changes to GltfIndexBufferLoader because implementing the wireframe required the index buffer to be available on the CPU. Index buffers are now loaded as typed arrays only in WebGL1 since it's not possible to get data from the buffer directly. With WebGL2, either buffers or typed arrays are fine.

[cesium-concierge]

Thanks for the pull request @j9liu!

• ✔️ 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.

Reviewers, don't forget to make sure that:

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

[ptrgags]

@j9liu for gl.TRIANGLES, this is working very nicely! I had some comments about making this more robust to handle triangle strips/fans

[j9liu]

@ptrgags updated, here's a Sandcastle with TRIANGLE_STRIP and TRIANGLE_FAN models to demonstrate that they work

[ptrgags]

@j9liu code updates look solid, and the new models are working properly.

One thing I noticed is that for some reason the GroundVehicle model doesn't seem to render properly when switched to wireframe mode. Any idea why this might be?

[j9liu]

@ptrgags I can't replicate the Ground Vehicle bug. It looks fine for me:

[j9liu]

Turns out on Linux, normal mapping doesn't work with lines because it handles the dFdx, dFdy functions differenly. I added a define to make sure the code doesn't try to use normal maps if it is rendered in wireframe.

@ptrgags let me know if this solves the issue for you.

[ptrgags]

@j9liu that still didn't work unfortunately... Even when I inspect the normals with a CustomShader, I get a black wireframe mesh.

However, I also tried forcing it to render UNLIT via CustomShader, that's working:

Sandcastle

[ptrgags]

@j9liu oh wait I think I fetched without pulling 😅, let me try again

[ptrgags]

@j9liu sorry for the false alarm, the changes are working:

had one small comment before I merge

[j9liu]

@ptrgags updated!

[ptrgags]

@j9liu looks good, I'll merge once CI passes!