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
@charset    : atarist
@lang       : 
@default    : Title
@help       : 
@options    : +g -i -s +x +zz -t4
@width      : 70
View Ref-File7.2.4.4  Printer drivers                                           TOS

The selection of printer drivers for GDOS is at present almost 
inexhaustible; the only bottleneck seems to be for some colour 
printers.

When working with printer drivers one should note that not all drivers 
are completely identical functionally. So when using, say, a laser 
printer there are not only extra functions, but some of the existing 
ones may be partly extended as well.

For NVDI printer drivers one can set the page format and the GEMDOS 
output device for v_opnwk. For outputting (colour) images one should 
use the vrt_cpyfm or vro_cpyfm functions. They can be addressed in 
NVDI for printer drivers (and IMG, etc.) exactly like the functions of 
the screen driver. The only difference is that rasters cannot be moved 
within a printer bitmap (source and destination MFDB with fd_addr == 
0L), as the printer bitmap generally consists of several slices that 
are handled sequentially. But this difference presents no 
restrictions, since copying within the device bitmap makes no sense 
for printer output!

If necessary, the printer driver buffers the bitmap in the display 
list should insufficient memory be available; there is therefore no 
need to hold the bitmap in memory with v_updwk until output.

If the bitmap has to be scaled, the program should not itself enlarge 
the bitmap if possible, but leave this work to vrt_cpyfm/vro_cpyfm. 
This improves the output quality, less data has to be buffered on the 
hard drive, and the printout is speeded up. Whether the driver is 
capable of scaling can be established with the vq_extnd call.

When outputting colour images in 8-colour mode, rasters should be 
treated before dithering with a correction function. Recommended is a 
gamma correction with an exponent of 0.3 to 0.4, so that the image 
does not appear completely dull and oversaturated. In TrueColor mode 
the driver performs colour correction, black separation and other 
quality improvements itself - bitmaps here should be sent without 
previous correction and without rasterising to the driver.

See Also: GDOS drivers   Bitmap format for printer drivers 
Minimum range of function