I used Display PostScript back in the early days at NeXT. It had a very fundamental performance problem. Since PS was designed as an interpreter and could first

I used Display PostScript back in the early days at NeXT. It had a very fundamental performance problem. Since PS was designed as an interpreter and could first be fully processed before rendering a page, DPS had essentially the same design. That meant that you had to parse the entire submitted DPS source before you could start doing any rendering (since there could be dependencies late in the submitted code which would influence earlier code.) So it wasn't a simple Z-ordered geometry - it really was a complex language. So, in practice, it was slow and there was no way to really optimize it without breaking compatibility. We were the first real users and thus the first to realize that we couldn't really compete with either simpler or more sophisticated technology (one faster, the other providing more features.) So it worked for our application as an OS GUI, but it was in many ways a dead-end.