convenience and efficiency, the OpenGL Shading Language defines an
assortment of built-in functions
- Expose some necessary hardware functionality in
a convenient way.
- Represent a common operations (clamp,
mix, etc.) that are
for the user to write, but may
direct hardware support.
- Represent an operation graphics hardware is likely
to accelerate at some point.
Programmers are encouraged to use
the built-in functions
equivalent code to perform similar computations.