[effectcompositor] Chaining multiple effects

Hi @xarray ,

We're attempting to use your excellent EffectCompositor snippet in OpenMW, but run into an issue trying to chain multiple effects together. I couldn't find any example of how to this (or if it's even supported), and my naive attempt of creating a hierarchy of effect nodes didn't work (only the last effect renders). Is this supposed to work or are we missing a feature? Any idea on how this would best be achieved? Here are some more details on what I tried: https://forum.openmw.org/viewtopic.php?f=6&t=4425&sid=c723cd8f0daf76d23e76dc14906a83e8#p48178
Another idea would be to write some code to "merge" two compositor definitions into one, but that doesn't seem trivial.

Thanks!