Calculated formula layers

[kirk23]

Live or half live  with "update" button  procedural layers that would be  a result of math calculation formula like  (layer1RGB+layer2RGB)*(layer5alpha-layer7R) =  resulting layer .    Ideally with kind of node based interface. But formula would be ok too.  Working even with those input layers switched off/set invisible  in Layers panel

Sometimes the current layers/groups etc system is just not enough for something complicated and makes it too complex and inconvenient to search through and figure out while some kind of formula with maybe kind of highlighting  for input layers world be instantly clear and more elegant in layers panel

[John Rostron]

How does what you are asking for differ from the Apply Image action?

John

[kirk23]

7 hours ago, John Rostron said:

How does what you are asking for differ from the Apply Image action? 

John

"Apply image"  use only single "Source" layer/image and what I am asking for is a kind of similar thing but working with several source layers/images at once  plus being  "live" or at least updatable with "refresh" or something button once I edit/move/scale/replace any source layer/image involved. 

What I suggested is similar to Mari procedural layers/masks having its own sub stacks of layers with it's own cross dependency onto another layers.  A thing that would be impossible to do and keep track of within a single layer stack.