Fixed Hidden Point Primitive Bug

[ProjectBarks]

create an entity with point graphics and change its show property to false it doesn't hide, instead, it positions itself in the center of the screen while still being visible.

this issue only occurs when I'm in a Ubuntu environment

Fixed by changing translucency in addition to point location when showing

This is in response to #8043

[cesium-concierge]

Thank you so much for the pull request @ProjectBarks! I noticed this is your first pull request and I wanted to say welcome to the Cesium community!

The Pull Request Guidelines is a handy reference for making sure your PR gets accepted quickly, so make sure to skim that.

• ❌ Missing CONTRIBUTORS.md entry.
  • Please add yourself to the contributors file!
• ✔️ 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.
• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

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

[OmarShehata]

Some thoughts:

• Consider hiding the point the same way that point clouds do here: https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Scene/PointCloud.js#L1177-L1178
  • The advantage there is that moving the point off screen produces no fragment, as opposed to rendering it with alpha 0.
• This incorrect line is still there: https://github.com/AnalyticalGraphicsInc/cesium/blob/453b3ff53517e46443ba95748d1c423e6ac19fbb/Source/Shaders/PointPrimitiveCollectionVS.glsl#L94

[ProjectBarks]

Thanks omar! Good suggestions.

[emackey]

Billboards are similar to points, do they have the same issue?

[ProjectBarks]

@emackey it doesn't appear to be an issue. Tested using this sandbox.

[mramato]

I can confirm this is fixed on my machine. Thanks @ProjectBarks this one really annoyed me.

@OmarShehata I'll let you handle the rest of this PR, merge when you are ready (or bump to Sean if you need a second opinion).

[mramato]

There are a bunch of local test failures in this branch. @ProjectBarks you probably aren't aware of this, but travis CI doesn't run the WebGL tests, so you should always run tests locally as well. (Assuming they are failing for everyone and not just me)

[mramato]

I actually can't reproduce the failures any more, I think I might have been missing that last commit? Either way this is good to go, @OmarShehata feel free to merge if you don't need a second opinion on the shaders.

[mramato]

@OmarShehata did you need to take another look at this or can we merge?

[OmarShehata]

Sorry for the delay here. This looks good to me.