Sun lighting option for Models and 3D Tilesets

[lilleyse]

If a model uses the KHR_materials_common extension or is a 2.0 PBR model, the shaders we generate use the Cesium sun as the light source.

This PR adds an enableLighting option to Cesium3DTileset, Model, and ModelInstanceCollection that controls whether models are shaded based on the sun direction (the default) or based on the camera direction. The latter is better when the sun is on the opposite side of the globe and the model just appears black.

This options also controls lighting for point clouds that contain normals.

The reason enableLighting can't be changed dynamically is we still don't have a good way of recompiling shaders for models. Until then this will need to stay as a constructor parameter.

TODO

• Add to entity API

gltf-pipeline PR: CesiumGS/gltf-pipeline#346

For https://groups.google.com/forum/#!topic/cesium-dev/vIMLLYxYx4g

[cesium-concierge]

@lilleyse, thanks for the pull request! Maintainers, we have a signed CLA from @lilleyse, so you can review this at any time.

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[pjcozzi]

Other than the point cloud lighting, I'm not 100% sure that we want this change - for "directionless" lighting I would rather go with AO + irradiance environment maps. A light on the camera doesn't always produce good results for edge on geometry.

[lilleyse]

Would it be okay to go with this low tech solution until then?

At least for PBR models the edge lighting looks pretty good because we still have environment lighting.

[pjcozzi]

I suppose - it is easy enough to deprecate. Consider renaming it to sunLighting, eyeLighting, etc.

[lilleyse]

Updated.

Originally I went with enableLighting to match the Globe.enableLighting, but sunLighting is a better name.

[cesium-concierge]

Thanks again for the pull request!

Looks like this pull request hasn't been updated in 30 days since I last commented.

To keep things tidy should this be closed? Perhaps keep the branch and submit an issue?

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[lilleyse]

Closing for now - we can restart this later if there is more need, but it will probably be a scene wide option for #6553.

[cesium-concierge]

Congratulations on closing the issue! I found these Cesium forum links in the comments above:

https://groups.google.com/forum/#!topic/cesium-dev/vIMLLYxYx4g

If this issue affects any of these threads, please post a comment like the following:

The issue at #6160 has just been closed and may resolve your issue. Look for the change in the next stable release of Cesium or get it now in the master branch on GitHub https://github.com/AnalyticalGraphicsInc/cesium.

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[lilleyse]

Parked on https://github.com/lilleyse/cesium/tree/enable-lighting

[pjcozzi]

@lilleyse if you haven't already, probably a good idea to link to that branch (and all parked branches) from an issue.

[hpinkos]

@lilleyse why did you park this on your fork instead of our repo? And yes, please open an issue in this repo if one doesn't already exist

[lilleyse]

I didn't want to keep a stale branch around, but still wanted somewhere to look at the code later. Should I push the branch here instead?

This issue is being tracked in #6553

[hpinkos]

@lilleyse yes, I think that's preferred so it would be easy for anyone (not necessarily just you) to pick it back up and start working on it if there's an interest. So yeah, I would make a branch in this repo and add a link to it in #6553 so anyone interested in seeing the work on it would be able to find it.

[lilleyse]

Ok, I restored the branch and updated the link in #6553.