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DPS/NeWS

Our approach in MOVIE is to design an integrated MovieScript-based model for graphics, GUIs and visualization. We adopt the original PostScript model for scalable two-dimensional graphics as defined in [Adobe:87a] and we extend it by including other graphics subsystems. Even in the PostScript domain, however, we face uncertainties due to competing models offered by the DPS server from Adobe Systems, Inc. and the NeWS server from Sun. Since none of these Postscript extension models is complete (e.g., none offers the model for three-dimensional graphics), we don't follow any of them in building the MovieScript extension. Only the intersection of both models, given by the original PostScript model for printers, is adopted ``as is'' in MOVIE, and we build custom extensions towards windowing and event handling, compatible with other Open Systems components. The conflicting extension models of DPS and NeWS are not part of the MovieScript design but these language sectors can be accessed from the MovieScript code since the MOVIEDPS/NeWS interface model supports programmability of remote PostScript servers.

Remote PostScript devices such as NeWS or DPS servers are accessed from the MovieScript code by the operators gop and gdef. The syntax of gop is the following:

where key is the literal name, and are numbers, code is a MovieScript object capable of defining some remote PostScript code, and rop is the MovieScript operator (with the prefix ``r'' standing for ``remote''). Here, gop installs the user-defined graphics operator (implemented as a PostScript procedure) in the remote PostScript server and it also creates the local MovieScript operator rop associated with this remote operator. Both local and remote operators are associated with the common name, specified by key. The code object can be a MovieScript procedure or string. The execution of rop consists of sending arguments from the MOVIE operand stack to the NeWS/DPS operand stack, executing remote procedure in NeWS/DPS, associated with key and previously installed in NeWS/DPS by gop, finally transporting back output objects from NeWS/DPS to MOVIE.

The associated gdef operator is simply a sequence: { gop def }, that is, it installs rop in the local dictionary under the name key. In other words, the action of gdef is fully symmetric on local (MOVIE) and remote (NeWS/DPS) servers. The gop output format can be used to handle rop differently-for example, by installing it as an instance method within the MovieScript class model.

MovieScript support is also provided to control the connection status and buffering modes along the PostScript-based communication lines.

The interface model described above was developed first for the NeWS server [Furmanski:92d], and it is now ported to DPS [Podgorny:92b].



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Guy Robinson
Wed Mar 1 10:19:35 EST 1995