Vertical exaggeration for 3D Tiles

[jjhembd]

This PR extends dynamic terrain exaggeration to 3D Tiles.

There are some differences in the approach for terrain vs. 3D Tiles. For on-the-fly exaggeration, we need 2 things at each vertex:

1. Ellipsoid normal at the vertex position. This is the local "up" direction along which exaggeration will be performed.
2. Height above the ellipsoid.

The current terrain exaggeration computes these 2 values on the CPU and uploads them as a separate vertex buffer. This works well for terrain, because it is (a) static and (b) relatively light-weight.

For 3D Tiles, this PR computes normals and heights for each vertex on-the-fly, in the vertex shader, using a local approximation to the Earth curvature. This reduces the load on GPU bandwidth, and simplifies handling of tilesets which are being dynamically positioned via a model matrix.

Here is a local Sandcastle link demonstrating exaggeration of the Google Photorealistic 3D Tiles.

Remaining tasks:

• Update public API. Exaggeration is still controlled via globe.terrainExaggeration and globe.terrainExaggerationRelativeHeight. This should really be changed to scene.verticalExaggeration and scene.verticalExaggerationRelativeHeight.
• Support exaggeration of TileBoundingSphere and TileOrientedBoundingBox
• Update CHANGES.md

[cesium-concierge]

Thanks for the pull request @jjhembd!

• ✔️ 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.

[jjhembd]

@lilleyse can you take a first look? I am still working on a few peripheral things, but the main logic is ready.

[jjhembd]

I pushed an update to exaggerate bounding boxes and spheres. All bounding volume types are now supported.

Here is an updated local Sandcastle with bounding box QC.

[lilleyse]

Does entity clamping (#11604) work on exaggerated 3D Tiles?

[jjhembd]

I don't think it does as-is, but it could be extended to support exaggerated tiles. #11604 depends on #11581. In that PR, the pickModel function has access to frameState, so it should be fairly straightforward to account for exaggeration there.
@ggetz am I correct here?

[ptrgags]

@jjhembd What's the status of this thread? Is this something beyond the scope of this PR? if so, is there an issue for it?

[ptrgags]

I linked to this thread in #11604 so we don't forget about this.

[jjhembd]

@lilleyse thanks again for the feedback! I think this is ready for another look.

[jjhembd]

Thanks again for the feedback @ggetz! I think I addressed everything you mentioned.

[ggetz]

Sorry, @jjhembd, but one other thing I noticed while testing this out on other tilesets is that OSM Buildings...

const osmBuildingsTileset = await Cesium.createOsmBuildingsAsync();

...do not show up if the exaggeration is set to anything other than 1.0.

[ggetz]

But other than OSM Buildings, exaggeration is working great with the other tilesets!

[ptrgags]

@jjhembd I did a partial review pass focused on the updates to Model and automatic uniforms since these are relevant to #4196. Had a few comments there.

[jjhembd]

Sorry, @jjhembd, but one other thing I noticed while testing this out on other tilesets is that OSM Buildings...

const osmBuildingsTileset = await Cesium.createOsmBuildingsAsync();

...do not show up if the exaggeration is set to anything other than 1.0.

Thanks again for catching this @ggetz. A tile's bounding rectangle was being overwritten. This is fixed now, and OSM buildings exaggerate as expected:

[jjhembd]

Thanks for your feedback @ptrgags! I think I addressed everything you mentioned. Can you give it a final check, and merge if OK?

To verify both legacy and new behavior, you can check the Terrain Exaggeration and 3D Tiles Vertical Exaggeration Sandcastles.

[ptrgags]

@jjhembd I just noticed something, if you enable the Scene Mode Picker and switch the mode to CV, the globe doesn't render correctly. modified local Sandcastle with sceneModePicker

Expected result from hosted Sandcastle:

[ptrgags]

@jjhembd okay I've reviewed the sandcastles, the code, and read through the older comment threads (I had a couple questions there about the status of lose ends). I had a few questions.

[ptrgags]

The updates look good, thanks @jjhembd!

[syzdev]

@jjhembd The code comments here are incorrect.

cesium/packages/engine/Source/Scene/Model/VerticalExaggerationPipelineStage.js

Lines 5 to 15 in 0734229

	/**
	* The custom shader pipeline stage takes GLSL callbacks from the
	* {@link CustomShader} and inserts them into the overall shader code for the
	* {@link Model}. The input to the callback is a struct with many
	* properties that depend on the attributes of the primitive. This shader code
	* is automatically generated by this stage.
	*
	* @namespace VerticalExaggerationPipelineStage
	*
	* @private
	*/

[jjhembd]

@syzdev thanks for catching that! I submitted a fix in #11969.