Proposal: InstancedMesh.updateRanges -> array of update ranges

[trusktr]

Description

It looks like only a single updateRange is supported, and gl.bufferSubData gets called only once for that range.

Solution

To allow higher control of optimization by Threejs users, a new .updateRanges property could be an array of update ranges, and in WebGLAttributes it call loop on those and call gl.buffSubData for each range.

Alternatives

n/a

Additional context

This may allow multiple sets of instances to be updated per frame.

For example, if someone has 1 million instances, maybe they only want to update 10 through 20, 1_000 through 1_100, and 500_000 through 500_005. For this they can define three update ranges, and avoid having to, at minimum, define a single range from 10 through 500_005. The array will allow uploading data for 115 instances instead of (at least) 499_995 instances.

[Mugen87]

It was tried to implement this once, see #13393. But it seems there was a performance issue that caused the OP to close the PR.

[trusktr]

Yeah that's the idea. Yeah, creating and replacing arrays every frame is not gonna be ideal. We'd need to re-use objects if we'll be adding/removing them.

Another idea is instead of an array of objects, it could be a Map<number, number> or Record<number, number> (pairs of start,count), then iterating the key-value pairs.

With an array of objects, or with a map, an updateRangeCount would make it easy to specify how many update ranges to iterate over (default to all).

For back compat, updateRange could stay the same, and a new updateRanges (plural) could have multiple ranges.

[Mugen87]

Fixed via #27103.