[FR] Add step and smoothstep functions

[SpotlightKid]

... so they can be used with shady.

Here are implementations for float (after the example here). Should be relatively easy to make them generic:

proc step*(a, x: float): float =
  if x < a:
    0.0
  else:
    1.0

proc smoothstep*(a, b, x: float): float =
  # Scale, and clamp x to 0..1 range
  let x = clamp((x - a) / (b - a), 0.0, 1.0)
  x * x * (3.0 - 2.0 * x)

Then update shady to add these functions to glslFunctions.

[treeform]

Is it same as

• https://registry.khronos.org/OpenGL-Refpages/gl4/html/step.xhtml
• https://registry.khronos.org/OpenGL-Refpages/gl4/html/smoothstep.xhtml

[SpotlightKid]

Yes.