Proposal: Add standard library step functions

[kwokcb]

Proposal

It does not seem that there is a step function as part of the standard library. At least I could not find them. You can do it with ifgreater or a degenerate form of smoothstep (high == low) but it more expensive or troublesome.

As this is an intrinsic in languages like GLSL (variants) nd OSL, adding a proposal that step be added.

If not an intrinsic it would be useful to add supporting ifgreater or (ifless) definition variants which work with tuples to avoid having to add explicit separate and combine nodes.

Note that some implementations like split use aastep which allows a filter width for anti-aliasing. step and aastep would both be useful as standard nodes.