Function y=x is called "linear interpolation"

[Victor Sergienko]

In chapter https://thebookofshaders.com/05/, y = st.x dependency is called "linear interpolation".

This is not the right term. Mapping from x to y is called a function, and y=x is one of the simplest examples of a linear function.

[Victor Sergienko]

Another comment about "interpolation" term in https://thebookofshaders.com/05/.

The informal definition of smoothstep() is quite confusing, given that no definition of interpolation was given (and the term was so far encountered once in a wrong context).

Given a range of two numbers and a value, this function will interpolate the value between the defined range. The two first parameters are for the beginning and end of the transition, while the third is for the value to interpolate.

This left me confused. I would say something like:

values outside of edge0 evaluate to 0, values outside of edge1 evaluate to 1, and values between edge0 and edge1 smoothly grow from 0 to 1.

Or outright give a mathematical definition like NVidia doc does:

• Returns 0 if x < a < b or x > a > b
• Returns 1 if x < b < a or x > b > a
• Returns a value that smoothly grows in range [0,1], for the source values from [a,b]` range.

[Christopher Rollings]

I think these sound reasonable.. maybe you could create a PR?