Hidden entity remains visible on Linux

[mathiasfn]

1. A concise explanation of the problem you're experiencing.
   If i 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

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.
   I've created an example to demonstrate my issue:
   https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/#c=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

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.
   I need to be able to toggle entities visibility rather than destroying and recreating

4. The Cesium version you're using, your operating system and browser.
   Cesium version: 1.60
   Operating system: Ubuntu 18.04.2 LTS
   Browser: Google Chrome Version 76.0.3809.87 (Official Build) (64-bit)

[OmarShehata]

Thanks for the Sandcastle example @mathiasfn . I'm dual booting Windows 10 and Kubuntu, and I can confirm that this only happens on the Linux side.

I suspect the problem is different driver implementations, so it's something we're doing in our shaders. The logic to hide points happens in the shader. You can see where this gets initially packed as a shader attribute in PointPrimitiveCollection, and here's where it's used in the shader:

https://github.com/AnalyticalGraphicsInc/cesium/blob/54acd32f50c332605615a7b37b774c04690ef55c/Source/Shaders/PointPrimitiveCollectionVS.glsl#L94

What's quite peculiar to me here is that this shader is "hiding" points by multiplying the xyz by 0, which may explain why it gets centered at the origin instead of actually disappearing (but then why does this work fine on Windows?)

We can fix this if we multiply the color by the show value instead, so at the bottom of that shader it would be:

v_color = color;
v_color.a *= translucency * show;
v_outlineColor = outlineColor;
v_outlineColor.a *= translucency * show;

[mramato]

Duplicate of #7557?

Only happens for me under Nvidia on linux (my intel card can't reproduce it) @OmarShehata sounds like a good PR to open to get this fixed.

[OmarShehata]

Sean mentioned that the technique of hiding a point by multiplying xyz by 0 is actually intentional here. The idea is to move it out of the clip space, so it's not generating fragments at all, effectively discarding it, as opposed to just making it transparent.

Point clouds are hidden in a similar way:

https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Scene/PointCloud.js#L1177-L1178

I can open a PR for this soon.

[OmarShehata]

This was fixed in #8054.