Core Graphics is an implementation of the same imaging model as Postscript and is very close to PDF (and can easily be used to render PDF documents).

With Display Postscript you could type in real Postscript commands into your C/Objective-C source file and it was pre-processed into actual code.

  defineps PSWGrayCircle( )
    newpath
    10.0 10.0 5.0 0.0 360.0 arc
    closepath
    0.5 setgray
    fill
  endps

And it could be called just like any other function, including with parameters.

NeXT used display PostScript as it's graphics language. When apple was working on OS X they wanted to continue, but we're worried about adobe licensing costs, and so ultimately went with PDF instead