Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uupsi!sunic!news.funet.fi!uta!cshera
From: cshera@uta.fi (Heikki Rasim{ki)
Newsgroups: comp.sys.atari.st.tech
Subject: Atari graphics
Keywords: VDI
Message-ID: <2824@kielo.uta.fi>
Date: 30 May 91 08:52:03 GMT
Distribution: comp
Organization: University of Tampere, Finland
Lines: 39


	Hello !

	I recently read some books of Atari ST internals by Abacus
        and found some odd things I hope someone can explain to me.

        1) set color representation, opcode 14 trap #2
           Intensity of red, green and blue can have values from 0 to 1000.
           What is done to this information ? I know it somehow ends up to
           video shifter registers where intensity can range from 0 to 7.

        2) open workstation, opcode 1 trap #2
           intin(0) Device identification, given on loading Device Driver
           contrl(6) Device identifier
           What these two parametres should be ? I suppose this is a GDOS
           function to load a device driver from GIOS. It is said that it won't
           work because of missing device drivers. Can I make one and put it
           into GIOS ( how ) ?

        3) previous function returns among other things  screen resolution and
           number of colours available. How these two things are handled in Atari ?
           How electronic beam inside tv or monitor knows that this time it
           is supposed to plot 640 times per line insted of 320 it did last month
           or to draw twice as many lines per screen as it did last time ?
           
           With my stumbling english I think I learned that colours are produced
           by MMU and SHIFTER together. In most odd way I think. Is it usual
           among computers to have they video-RAM fullfilled with colour indexes
           instead of their RGB-values ? If so, what's wrong with latter case ?
           It wouldn't need any video shifter registers to limit colours to 16.

           
        Any help aprpriapro... eh, valuated high.
        Thank you in advance, curiosity is killing me.


        Heikki Rasim{ki
        cshera@uta.fi