Improved point cloud eye dome lighting at varying resolutions

[IanLilleyT]

For #8113

Point cloud eye dome lighting works by comparing a pixel's depth with neighbor depth values to create a silhouette. Currently the depth texture uses nearest filtering which is a problem when the EDL radius is less than 1, because it will only sample depths within the center pixel. This is a problem with smaller pixel ratios.

I switched it to linear sampling which introduces a small border between point clouds and the background. For example, the gray lines in #8216 become black. This is a pretty uncommon setup, as explained in the issue.

Old:

New:

0.25x res

Old 1.0x res

New 1.0x res

Old 0.25x res

New 0.25x res

Old 1.0x res

New 1.0x res

Old 0.25x res

New 0.25x res

[cesium-concierge]

Thanks for the pull request @IanLilleyT!

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Reviewers, don't forget to make sure that:

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

[IanLilleyT]

Made a new version of the eye dome lighting shader which uses Nearest sampling and manually interpolates the depth values inside the shader. This way the shader can check for out-of-bounds depth values and still get a clean interpolated depth, best of both worlds.

The main downside is it requires 10 textures reads per pixel vs 6 from before. This might be ok since the extra reads are from adjacent pixels. The image quality is exactly the same as pre-PR but now works at different resolution scales and non-integer EDL radius.

Ready @lilleyse

[lilleyse]

The 10 vs. 6 pixels seems to not hurt the fps. I set the view to look just at EDL pixels and cranked resolution scale to 4x (roughly 15360x8640 on my monitor). Both this branch and master rendered at 8fps consistently. Sandcastle

I also like that the new approach doesn't have the black border artifacts that the first approach had.