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.

Start by locating the Uber shader and reviewing how its HLSL handles the clipping primitive. Compare that structure with the shader graph, subgraph, and custom-function possibilities mentioned in the issue. Done would mean a documented modular approach for reusing clipping behavior, with any performance impact evaluated.