Add ground atmosphere

[bagnell]

• Can be toggled with Globe.showGroundAtmosphere and is enabled by default.
• The fade in/out for the night side of the globe can be changes with Globe.nightFadeOutDistance and Globe.nightFadeOutDistance.
  

[cesium-concierge]

Thanks for the pull request @bagnell!

• ✔️ 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.
• Works (or fails gracefully) in IE11.

---

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

🌍 🌎 🌏

[hpinkos]

How does this play with Globe.enableLighting? It looks like we're also defaulting that to true now and setting it to false seems to have no effect.

[bagnell]

If showGroundAtmosphere is true, then enableLighting shows lighting with terrain vertex normals when available. When showGroundatmosphere is false, it works the same as before.

[pjcozzi]

Code looks good at ultra quick glance!

[bagnell]

The ground atmosphere is now computed per-fragment in GlobeFS for better lighting of the day/night transition. It is only enabled when the camera is above the nightFadeOutDistance, otherwise it is disabled with a #ifdef.

This is ready for review.

[bagnell]

Bump.

[lilleyse]

This is a good example of what @pjcozzi means with looking washed out on different types of imagery.

[lilleyse]

I also agree that a "Globe Lighting" Sandcastle that has toggles for

• Ground Atmosphere
• Enable lighting
• Switch between shading with terrain vertex normals or not
• Water shading
• Sliders for controlling the fade in and fade out distances

would be pretty useful to have generally, especially as this change rolls out and people are interested in customizing it. We could just point them to the demo.

[lilleyse]

I tweaked some of the parameters for the fade in - it's a little smoother now and looks a bit better when enableLighting is on. e1005fe

Though setting nightFadeOutDistance didn't seem to make a difference even when set to 0. Is there some hidden minimum?

[bagnell]

Though setting nightFadeOutDistance didn't seem to make a difference even when set to 0. Is there some hidden minimum?

The nightFadeOutDistance is the distance until it fades to a fully lit atmosphere. So if you set it less than lightingFadeOutDistance you won't see a difference. Set it to something greater than lightingFadeOutDistance but less than nightFadeInDistance and you'll see what I mean.

[bagnell]

@lilleyse This is ready for another look.

[lilleyse]

Looks really good - the water shading from far out is now much nicer now! I added a few last tweaks. Mainly just upped the specular brightness and changed the night fade in.

There is one bug in the atmosphere demo where clicking the reset button doesn't seem to update the sliders.

Does anyone else want to check this out before we merge? Demo of this branch here:

http://cesium-dev.s3-website-us-east-1.amazonaws.com/cesium/atmosphere/Apps/Sandcastle/index.html?src=Atmosphere.html

[pjcozzi]

Looks great at quick glance!

[bagnell]

There is one bug in the atmosphere demo where clicking the reset button doesn't seem to update the sliders.

Fixed.

[lilleyse]

I think the proper way to do this in knockout is:

viewModel.lightingFadeOutDistance = defaultLightFadeOut;
viewModel.lightingFadeInDistance = defaultLightFadeIn;
viewModel.nightFadeOutDistance = defaultNightFadeOut;
viewModel.nightFadeInDistance = defaultNightFadeIn;

[bagnell]

Thanks. Updated.

[bagnell]

I also noticed that the fog was broken, but it's now fixed. This is ready for another look.

[lilleyse]

Looks good to me. Thanks @bagnell, this is a really nice visual quality improvement!

[lilleyse]

Just added some last bits of documentation: b75d1cf