Hey!
So that note to myself has a bit of a long story...
Basically, SetMesh() is called every frame when there's an animated effect going on. If it's working as intended, it only gets enabled when an effect actually needs movement, so <c=rainbow> won't invoke it if the animation speed of the gradient is set to 0. This could be optimized further though, currently every time it calls SetMesh(), it rebuilds the mesh from stored data entirely. So it doesn't re-parse the entire string like Rebuild() does, but it does re-create the mesh with the appropriate time data. I *think* this could be improved if it checked which vertices actually needed to update position/color, and then only changed those. But ultimately, I didn't go with this because SetMesh() is already called every frame as STM reads out... so you'd end up with variable CPU load for a given string, and I thought it'd be better to just keep it consistent.
The actual end goal of this note is... someday I really want to make it so that all of STM's time-based effects are handled GPU-side instead of CPU-side. So the timing data would just be fed to STM's shader , and it'd just do it's thing automatically every frame, instead of STM needing to update anything. I'm still just waiting on the shader update I commissioned that will handle new dropshadows and outlines before I look further into this route, so I have something to build on. There's still a lot of things to consider with this method, too.
But also, for the current method there probably is way more that can be optimized, even while still updating every frame on CPU. I may have to take another deep-dive into that shortly to see if there's anything I missed that I'd know how to handle better today.
So until then, all I can really say is... cut down on animated effects or text box size, if possible. The animated effects are really just meant for text boxes about the size of the Paper Mario games at largest, so uuuuuusually a mesh of that size updating every frame isn't too bad, so it's been left as-is for the time being.