Topic       : TOS - The Operating System
Author      : 
Version     : tos.hyp (December 19, 2008)
Subject     : Programmieren/Atari
Nodes       : 3010
Index Size  : 93790
HCP-Version : 5
Compiled on : Atari
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@default    : Title
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View Ref-File13.11.3.3  How can I tell the viewer what is to be shown?          TOS

Because of the XAcc2 protocol, the application knows which message- 
groups are supported and these messages may be used for communication 
if the application has the data already in memory (and not within a 
file).

Use the VIEW_xxx messages (discussed below) when the data to be viewed 
is contained in a file. With these messages the application has 
extensive control over what is happening. These messages may be used 
if, and only if, the strings '2View' or 'NView' are found in the 
viewer's Extended XAcc name. This should normally be the case, though.

This may be a problem if the viewer has been started by the 
application. In this case I would suggest to try to send the messages 
and see what happens. If the viewer does not support them, no reaction 
is given (as unknown messages should be ignored!). Otherwise, the 
viewer will send a response.

The viewer is strongly recommended to support the VA_START message! Of 
course this has to be tested in its protostatus (if possible, see 
above).

There is no explicit support of the Drag&Drop protocol, as it was 
mainly a MiNT-specific extension (though it is included in MultiTOS 
and later in MagiC), but programs running under MiNT should understand 
this protocol!

All other protocols, of course, may be used to communicate with the 
viewer (as long as they provide some method to determine whether or 
not they are supported).

Please keep in mind that pointers to strings in AES messages have to 
point to global-readable memory (if running in an environment with 
memory protection)!