Topic       : TOS - The Operating System
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Version     : tos.hyp (December 19, 2008)
Subject     : Programmieren/Atari
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Compiled on : Atari
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View Ref-File13.11  View protocol                                               TOS

The View protocol was developed by Peter Seitz and Dieter Fiebelkorn 
to make it possible for a GEM application to display files (using an 
external viewer) without being forced to implement a viewer for the 
various file formats itself, and to provide a uniform method of 
communication between the application and the viewer (so that the 
application can use any viewer, rather than just one particular 
viewer).

There are already several applications that can be used as viewers. 
They are GEM-View(Dieter Fiebelkorn), 1st-View/1st-Guide (Guido 
Vollbending), and ShowImage (Peter Seitz). When installed as desk 
accessories, these applications can be instructed (by other 
applications) to view files.

This experimental version of the View protocol is implemented in GEM- 
View and ShowImage. IT IS STRONGLY RECOMMENDED THAT ALL PROGRAMMERS 
USE AND EXPERIMENT WITH THIS PROTOCOL! We hope that eventually it will 
become a standard. Suggestions and comments are welcome; please send 
them to Peter Seitz at one of the following addresses:

  Peter Seitz, Robert-Koch-Str.6, 63225 Langen, GERMANY
  E-Mail (Internet): seitz(at)rbg.informatik.th-darmstadt.de
                  or seitz(at))isa.informatik.th-darmstadt.de

This protocol should be quite easy to implement for both the writers 
of viewers and the writers of applications. It should provide 
substantial benefits for the user as well, since he will be able to 
use his favourite viewer with all applications.

-Peter Seitz

In the following dicussion, 'viewer' refers to the desk accessory or 
application that is used to display the file(s) and 'application' 
always refers to the program that requests the services of the viewer.

13.11.1  The purpose(s) of the View protocol
13.11.2  Using the View protocol
13.11.3  Implementing the View protocol
13.11.4  The VIEW_XXX messages
13.11.5  The View protocol messages