Unified time slicing tasks

[pjcozzi]

To throttle work on the main thread like:

• Quadtree tile updates
• Billboard/label terrain clamping
• Model texture/buffer creation. WebGL resource creation in general.
• Compute pass, Add compute render pass #751, since imagery reprojection uses it.

Right now, each has their own system, which does not provide real control over avoiding dropping frames.

[pjcozzi]

• Starting at 25:00 - https://www.youtube.com/watch?v=QVvHtWePQdA

[mramato]

For non-immediate tasks in Cesium, requestIdleCallback looks like it could be really useful. It just got added to Chrome Canary. Not sure how much traction it has for other browsers.

[mramato]

Here's a much better write up on requestIdleCallback.

[pjcozzi]

There is some work-in-progress in the 3d-tiles branch: JobScheduler.

[pjcozzi]

This will also expand into scheduling work across workers, e.g., for geometric decompression. Users may just schedule a task, and it might have to execute time sliced in the main thread or it may be scheduled on a worker.

CC #1487

[pjcozzi]

There is not a ton of information on this web apps so we will need to look at desktop/console engines. Keep in mind that web workers are much more limited.

• Frostbite
• id Tech 5
• C4 Engine

[mramato]

There are also time-sliced tasks that we don't currently do in core Cesium that we'll want to be able to take advantage of this, such as incremental CZML/KML parsing to avoid locking up the browser for large documents.

[lilleyse]

More notes, directly from the code:

Potential additional types:

• CPU - e.g., for getting terrain heights for billboards/labels
• GPUCompute - e.g., for reprojecting imagery using GPGPU
• Content specific - e.g., favor terrain over buildings or vice versa

[lilleyse]

More thoughts about expanding the job scheduler to go beyond renderer resources: #5249 (comment)