Performance issue with Label (num characters) and CLAMP_TO_GROUND

[alarkbentley]

What happened?

Adding entities in Cesium.js using HeightReference = CLAMP_TO_GROUND is generally very costly for performance. The problem seems worse with Labels than Billboards, and strangely enough the performance decreases with not only the number of entities but primarily the length of the text labels (number of characters).

Rendering 1000 labels with 5 characters works quite well. But if I increase the number of characters to 20 or 100 the application becomes unusable. This only an issue when HeightReference is used to clamp the entities to underlying terrain.

As the letters are not individually placed relative to ground I see no reason why the number of characters should effect performance here.

Reproduction steps

1. Make sure "Clamp to Ground" is active
2. Enable "1000 Entities" (should work fine, 60fps)
3. Enable "100 Characters" (unusable, browser hangs)

Sandcastle example

https://sandcastle.cesium.com/#c=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

Environment

Browser: Google Chrome Version 138.0.7204.97 (Official Build) (64-bit)
CesiumJS Version: 1.131
Operating System: Windows 11

[javagl]

Just cross-linking to the forum thread here: https://community.cesium.com/t/performance-issue-with-label-num-characters-and-clamp-to-ground/41854/

[ggetz]

Fundamentally, I think this is due to #8481. However, I'll leave this open as it's own issue since it brings up the specifics of dealing with labels with each character being a billboard under the hood.

[yeminxuan]

The distanceDisplayCondition property should be able to temporarily solve this problem, using point aggregation to display at a distance @alarkbentley

[alarkbentley]

@yeminxuan It does not, even if I add a distancedisplaycondition that culls all billboards at start I can still reproduce the problem using the steps above.

You can try this updated Sandbox

[mzschwartz5]

I'm going to pick up investigation here, see if this is related to the issue @ggetz linked. As @alarkbentley commented in the forum post, it's pretty clear that there's some connection to clamping here, specifically. So I hesitate to write it off as a globe picking performance issue - unless perhaps only clamped-to-ground objects participate in picking. Will find out!

[mzschwartz5]

This section of the flame graph captures the transition from 10 labels at 100 characters each to 1k labels at 100 characters each. It's pretty clear the main problem is picking (as @ggetz said above). GlobeSurfaceTile.prototype.pick accounts for something like ~90% of the total time (between the three bars within Clock.tick and Scene.render).

Are other parts of this transition slow? Probably, but they're currently absolutely dwarfed by the picking call time.

[alarkbentley]

@mzschwartz5 I would be curious to see a flame graph when transitioning from 5 characters to 100 characters (as the reproduction steps states). Adding more labels it makes sense that we get more picking calls, but adding characters should not require more globe picking.

@ggetz Do we have any hope of solving the globe picking performance in near term? The linked ticket is from 2019 and latest comment is from march this year.