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Display PostScript

NeXT Computer Inc designed Display PostScript (or DPS) for their series of Unix-based personal computers starting around 1987. Display PostScript was developed with (or given to) Adobe, and made an official Adobe product with its own standards documents and licensing requirements.

Display PostScript is a fairly limited expansion on the original PostScript language. In order to support interactive, on-screen use with reasonable performance, a few changes were needed:

DPS did not, however, add a windowing system. That was left to the implementation to provide, and DPS was meant to be used in conjunction with an existing windowing engine. This was often the X Window System, and in this form Display PostScript was later adopted by companies such as IBM and SGI for their workstations.

On the NeXT system a completely new windowing engine was written, to take full advantage of their object oriented operating system. The windowing system itself used PostScript to draw items like titlebars and scrollers. This, in turn, made extensive use of pswraps, which were in turn wrapped in objects and presented to the programmer in object form.

Apple's Mac OS X operating system now makes use of a similar imaging model to Display PostScript, but does not have the same level of programmability. The new system, known as Quartz, is based on the PDF model in which the source of the image is not the PostScript code itself, but the result of interpreting that code. It keeps the basic graphics primitives, font handling and measurements, and in many cases looks and feels like DPS. It is not entirely clear why this happened, but speculation suggests that Adobe was asking for a high licensing fee.

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