BatchedMesh: Add fallback for when the multi draw extension is not supported

[gkjohnson]

Related issue: #22376, #27111, #27170

Description

Adds fallback for rendering BatchedMesh when multi draw is not supported by calling "drawArrays" multiple times in a tight loop. From testing even when the multi_draw extension is not used we still get some performance benefits since we don't have to change material uniforms for individual objects.

cc @RenaudRohlinger

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
656.7 kB (162.8 kB)	656.6 kB (162.8 kB)	-176 B

🌳 Bundle size after tree-shaking

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

Filesize dev	Filesize PR	Diff
449.2 kB (108.8 kB)	449 kB (108.8 kB)	-176 B

[Mugen87]

I'm not sure about this. Wasn't the plan to require WEBGL_multi_draw for BatchedMesh usage?

When we require certain WebGL features, developers hopefully ask at browser developers to finally support certain extensions like WEBGL_multi_draw. AFAICS, Firefox is the only major browser that doesn't support it for some reasons.

[gkjohnson]

I'm not sure about this. Wasn't the plan to require WEBGL_multi_draw for BatchedMesh usage?

I just thought I'd offer this as an easy-to-implement fallback option (thanks Renaud). Originally when considering a fallback I was thinking about a more complex implementation that would require maintaining both the original BatchedMesh implementation and the new multi draw one. But this is much simpler.

When we require certain WebGL features, developers hopefully ask at browser developers to finally support certain extensions like WEBGL_multi_draw. AFAICS, Firefox is the only major browser that doesn't support it for some reasons.

I'll leave whether to merge this for you and @mrdoob to decide - I would like FF to support multi-draw, too, though. A fallback like this might make more sense for #27170 considering InstancedMesh has already been supported and used in FF.

[mrdoob]

Considering how simple the fallback is, I think we should definitely do this 👍