Constantly creating and cancelling requests for 3D Tiles with requestRenderMode

[OmarShehata]

Sandcastle. This is a bit tricky to reproduce but I can reliably reproduce it:

1. Open the network tab, filter for "b3dm"
2. Move the camera a little bit.

After a bit of movement, you should start to see a seemingly endless stream of requests for b3dm tiles that keep getting cancelled and re-requested. This goes on for thousands of requests, for at least a full minute, even though it take seconds to actually load the given view if the tileset were not hidden.

This only happens with requestRenderMode: true. Seems like a bit of a corner case in the request cancelling system? @loshjawrence do you have any idea off the top of your head, or where in the code someone might want to look to debug this?

[mramato]

Sounds similar to #7786 which @loshjawrence already fixed once. requestRenderMode is important and this sounds like a major performance killer so we should fix this ASAP.

[mramato]

Preferably before the next release, but I would like to know more before tagging it that way.

[loshjawrence]

I'll have time tomorrow to look at this

[loshjawrence]

Update Sandcastle

Looks like the tileset's show boolean isn't updated from the more global primitives.show

[loshjawrence]

Potential fix #8081

[dennisadams]

I don't think #8081 properly solves the issue.
I have this issue also when I create a new tileset with show : false.
I can't however make scene.primitives.show = false, because I have other tilesets and primitives that I do want to show.
I haven't dug deep into your optimizations @loshjawrence, but maybe here in Cesium3dTileset.js:

if ((pass === Cesium3DTilePass.PRELOAD && (!this.preloadWhenHidden || this.show)) ||
    (pass === Cesium3DTilePass.PRELOAD_FLIGHT && (!this.preloadFlightDestinations || (!this.show && !this.preloadWhenHidden))) ||
    (pass === Cesium3DTilePass.REQUEST_RENDER_MODE_DEFER_CHECK && !this.cullRequestsWhileMoving && this.foveatedTimeDelay <= 0)) {
    return;
}

you should have a check of this.show also in the third condition line.
This worked for me:

(pass === Cesium3DTilePass.REQUEST_RENDER_MODE_DEFER_CHECK && ((!this.cullRequestsWhileMoving && this.foveatedTimeDelay <= 0) || !this.show))

but I don't know if it hurts any optimization.

[loshjawrence]

Thanks @dennisadams.

[OmarShehata]

This should now be fixed with #8081.