Access last value of pixel shader / Creating afterglow or decay effect

I’m not sure i understand exactly what you are after.
Normally mesh has it’s UV coords, witch is 2d plane try looking this:

i guess i need to see an example…

from what i’m guessing you want to reveal mesh by some sort of 3d function with feedback…
in that case you need to raymarch your function against mesh (try look here vvekend vvorkshops - raymarching basics | vvvv)
but it will be density function in your case… whitch is more complicated

also this might give you some hint Texture noise 3d | vvvv