Topic       : TOS - The Operating System
Author      : 
Version     : tos.hyp (December 19, 2008)
Subject     : Programmieren/Atari
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Compiled on : Atari
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View Ref-File7.2.2  About the GDOS                                              TOS

Several functions of the VDI can only be used properly after the 
installation of a GDOS from the AUTO folder. Basically a GDOS 
(Graphics Device Operating System) allows the loading of various 
device drivers and fonts, and then to use them.

The GDOS itself is completely independent of the device used. Only the 
post-loaded drivers that realize the VDI functions on the correspon- 
ding device are device-specific. With detailed knowledge of the driver 
format it is possible to use any - even exotic - output devices as a 
VDI output device.

With resident GDOS the number of available VDI functions increases, 
while all other functions remain fully functional or contain extended 
output capabilities. However this is not the case the other way round, 
functions that require GDOS lead to a crash of the computer if GDOS is 
not resident.



(Figure 1:The family tree of the GDOS family)

Therefore it is important to know in some cases whether a complete 
GDOS is installed at all. Atari has documented the following procedure 
for this purpose: The trap-dispatcher alters the input value -2 for 
register d0 only when a GDOS is installed. Many compilers make the 
function vq_gdos available, which returns a value of 0 when no GDOS is 
installed. This functions is based essentially on the following code:

vq_gdos:      move.w   #-2,d0
              trap     #2
              cmp.w    #-2,d0
              sne      d0
              ext.w    d0
              rts

Wichtiger Hinweis: vq_gdos liefert nur die Information, ob ein GDOS 
vorhanden ist, oder nicht. Es wird nichts darüber ausgesagt, um 
welches GDOS es sich handelt bzw. welche Fähigkeiten das installierte 
GDOS besitzt. So läßt sich mit Hilfe dieser Funktion beispielsweise 
das AMC-GDOS nicht von SpeedoGDOS oder NVDI unterscheiden.

Attention: The GEM versions of the Dutch software house "ABC" (ABC-GEM 
2.x) will crash at this call!

Allernatively there is also vq_vgdos (_vq_gdos):

vq_vgdos:     move.w   #-2,d0
              trap     #2
              rts

Als Rückgabe erhält man:

 Name           Value                GDOS Type 
 GDOS_NONE      -2                   GDOS not installed. 
 -              Any other value.     GDOS 1.0  or 1.2 
 GDOS_ATARI     0x0007E88A           GDOS 1.1 from Atari Corp. 
 GDOS_AMC       0x0007E864           AMC-GDOS from Arnd Beissner 
 GDOS_AMCLIGHT  0x0007E8BA           GEMINI-special GDOS from Arnd Beissner 
 -              0x3e5d0957           ttf-gdos from Trevor Blight 
 GDOS_FNT       0x5F464E54 ('_FNT')  FONTGDOS 
 GDOS_FSM       0x5F46534D ('_FSM')  FSMGDOS 
 -              0x66564449 ('fVDI')  fVDI 

The current (and more efficient) versions of GDOS are SpeedoGDOS and 
NVDI (as of Version 3.0), that, amid other things, permit handling 
vector fonts in TrueType, Type-1 or Speedo format. NVDI is also 
available in a special Macintosh version (NVDIMac), and permits any 
program that can ouput via GDOS (in conjunction with MagiC Mac) to 
make its output on Apple printers and in a network as well.

See also: ASSIGN.SYS file   VDI fundamentals   Style guidelines