13. The fragment shader code, cont.

• Unlike other normal basic types in GLSL,

  • the sampler can only declared at the global scope as uniform (cannot be a local variable)

  • the sampler cannot have a value; cannot be used in any arithmetic expressions

  • the only use of the sampler type is as parameter to a function:

    • User-defined functions can take sampler as a parameter

    • A number of built-in functions take samplers as parameters.