More modularity in the Uber shader

Describe the problem

I'm trying to implement a custom shader (adds elevation contour lines) that also leverages the clipping primitive, and it seems harder than it should be. The Uber shader is a monolith of code.

Describe the solution you'd like

Consider breaking up the hlsl into modules. Perhaps even modules could be leveraged by custom functions in shader graph. (That use out parameters.)

I should be able to include a module or subgraph that will make my shader clip the same way as the Uber shader (for example).

Describe alternatives you've considered

Better support for shader graph in general. Either subgraphs and custom functions or both. #34

Additional context

Caveat is I am rather new to hlsl and unfamiliar with best practices. If performance suffers from breaking out the code, I'd be curious to know exactly how much.

Inizia individuando l'Uber shader e verificando come il suo HLSL gestisce la primitiva di clipping. Confronta questa struttura con le possibilità di shader graph, subgraph e custom-function menzionate nell'issue. Il lavoro sarà considerato completato quando sarà disponibile un approccio modulare documentato per riutilizzare il comportamento di clipping e sarà stato valutato ogni eventuale impatto sulle prestazioni.