fix large entities on terrain/GroundPrimitives crossing IDL in 3D

[likangning93]

Part of #6951.

This doesn't fix the problem where ground primitives crossing the IDL are broken in columbus view and 2D, but that's going to be more complicated so I'll tackle that in a separate PR.

Give it a try here.

[cesium-concierge]

Thanks for the pull request @likangning93!

• ✔️ Signed CLA found.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

---

I am a bot who helps you make Cesium awesome! Contributions to my configuration are welcome.

🌍 🌎 🌏

[likangning93]

2D/CV and IE11: as well as it did in master... PR to follow for 2D/CV.

[hpinkos]

@likangning93 what's going on here? This is from the example you posted.

[likangning93]

@hpinkos I think that's a result of GeometryPipeline splitting the shadow volume but still drawing both of them in the same call. Something similar happens in 1.45, which can be replicated in 1.48 by changing the classification type. Here on 1.48. It also doesn't happen when scene3DOnly is set to true.

Might need to discuss with @bagnell what we can do about this... adjusting the shadow volume height should help a bit in the meantime though.

[bagnell]

The problem with the screen shot is that the volumes are split but not closed. If you split the volume and close both on each side of the IDL, it should be fine.

@likangning93 Can you add this? In GeometryPipeline, the triangles are split. Can you keep track of the new vertices added. Then you can project the vertices onto the plane of the IDL and triangulate. Then, add the new indices to the split geometry.

[likangning93]

The problem with the screen shot is that the volumes are split but not closed. If you split the volume and close both on each side of the IDL, it should be fine.

Still haven't wrapped my head around why this is from a stencil perspective, but simulating "closed" volumes by hand-splitting the rectangle does seem to work as described on Sandcastle.

@bagnell I'll open a separate issue and PR for this though.

[hpinkos]

@likangning93 here's the issue for seeing that seam when ground primitives cross the IDL: #4746

[bagnell]

This looks good. I'll merge. Don't forget about the other two PRs 😃