WebGLRenderer: Consider skinning / instancing when sorting objects.

[OndrejSpanel]

Description

Since #20135 a single material may be represented by multiple programs. In my scene I use the same material with instanced and non-instanced geometry. As a result I see frequent needsProgramChange = true in WebGLRenderer.setProgram.

This PR adds skinning and instancing as a secondary criterion for sorting into the default painterSortStable just after the material id.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
673.2 kB (166.9 kB)	673.4 kB (166.9 kB)	+199 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

Filesize dev	Filesize PR	Diff
452.9 kB (109.4 kB)	453.1 kB (109.5 kB)	+199 B

[OndrejSpanel]

@mrdoob @Mugen87 I think this is fairly trivial and obvious. Do you agree with the intention? Is there anything missing or in need of change / improvement?

[Mugen87]

I did not have the opportunity so far to review this change, sorry. At first sight I do not understand why it's necessary to alter the render lists for your use case so this needs some time for testing and debugging.

[OndrejSpanel]

When you have a scene where the same material is used for instanced and non-instanced geometry, the sorting currently sorts by material only. As a result, you can get your instanced and non-instanced geometry with the same material rendered in any order, like:

- plain material B
- plain material B
- instanced material B    *** program change
- plain material B        *** program change
- instanced material B    *** program change
- instanced material A    *** program change
- plain material A        *** program change
- instanced material A    *** program change
- plain material A        *** program change

After the change the order is:

- plain material B
- plain material B
- plain material B
- instanced material B      *** program change
- instanced material B
- plain material A          *** program change
- plain material A
- instanced material A      *** program change
- instanced material A

The number of program changes is reduced from 7 to 3. With skinned it works the same way.

[OndrejSpanel]

@Mugen87 This is hanging here for quite a long time. It is a fix of a minor performance issue. Could someone please check it and provide a feedback?

[Mugen87]

I agree this makes sense so let's give it a try. Sorry that this one got lost.

[OndrejSpanel]

Thanks for merging this. I understand it is a minor optimization which applies to a situation which is not very common, but the impact was measurable in my scenario.