Make `recolor` update on the same frame

[peterreeves]

I'm rendering a bunch of meshes and splats and I'm having trouble with Spark's recolor because it applies the change 1 or more frames late causing it to be noticeably out of sync with the color of the meshes.

I'm currently messing with custom shaders in Spark trying to force in a uniform that I can control to get instant recoloring, but I don't really want to have to maintain my own version of the shaders forever. Would it be possible for Spark to have a way to apply recolors in a frame-exact way? I've tried preUpdate: true but that doesn't seem to help me.

[mrxz]

The preUpdate: true is indeed supposed to ensure the update happens before rendering. While it did run the update logic, the rendering still commenced with the stale/old values, causing 1 frame of latency. I've created a PR to resolve the issue: #391

[peterreeves]

Thanks. Can you give me an idea of how expensive recolor is? I'm leaving it along most of the time but when a particular user triggered animation plays I'm setting it to a new color every frame for ~5 seconds. Tying it to preUpdate: true will mean that in addition to applying the color to the internal buffers, it's also going to do the full distance sort correct?

[mrxz]

Tying it to preUpdate: true will mean that in addition to applying the color to the internal buffers, it's also going to do the full distance sort correct?

Not entirely, while it does mark the current sort as dirty, this is still paced asynchronously from the main render loop. Additionally since changing recolor does not alter the accumulator mapping, rendering won't have to wait on the sort (it continues to use the last available splat ordering).

So while it strictly speaking does cause sorting where it technically doesn't have to, it's no different from the behaviour you'd get if the camera or the SplatMesh is moving or rotating. And if you happen to be doing that at the same time anyway, the recolor won't cost anything extra.

The key difference with preUpdate: true is when this takes place. The default schedules a timeout to handle it after the animation frame callback. With preUpdate it takes place synchronously in the animation frame callback. If you want the results to be visible in the same frame, preUpdate: true is needed (along with the fix from #391).