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-File7.2.4.11  Memory drivers                                           TOS

A memory driver is, in principle, a screen driver for which the output 
does not end up in the screen memory, but in another part of the 
memory, and which can then be processed further there.

The drivers available at present only support a monochrome bitmap, and 
have a logical resolution of 300dpi. Unfortunately the aspect ratio 
does not usually correspond to the current resolution of the screen, 
which has the result that circles, for instance, will be represented 
as ellipses.

The resolution of the bitmap may be set with v_opnwk, by writing the 
value 1 in ptsin[0..1] for width-1 or height-1 as well as in 
contrl[1]. After calling the function, the address of the bitmap is 
returned in contrl[0..1]. In addition it is also possible to set the 
bitmap size with vq_extnd. In that case it is also possible to pass a 
custom buffer; for this one sets contrl[3] to the value 3 and passes 
in intin[1..2] a pointer to the buffer.

Due to greater flexibility, one should give preference to off-screen 
bitmaps over memory drivers.

See Also: GDOS drivers   ASSIGN.SYS file