Re: SecondSight and shadowing

["geoff" <geoff@a2central.com.remove-zfj-this>]

  To: Toinet

The shadow process is hardware-based.  See the posting from Jawaid Bazyar in 
1994: 
http://groups.google.com/group/comp.sys.apple2/browse_thread/thread/6dedfe2b33b
f3eb2/a89ec1d061ab3a6b?hl=en&lnk=gst&q=second+sight+jawaid#a89ec1d061ab3a6b 
(the line may need to be copied and pasted in pieces since the A2central 
editor is wrapping the text).

It looks like the graphics memory which the Second Sight shadows has to exist 
in the Mega 2 memory (hence the card needs to work in a slot with the M2BA0 
pin).  Unless somebody understands the GS hardware better than I do, I don't 
think the Second Sight can read memory from the fast RAM IIgs banks--which is 
what it looks like you are proposing).

My impression is that a software solution is the only way to implement a 
higher desktop resolution.

Wouldn't a 640x400x2 be easier to implement and faster to get out the door 
(since that is the native 640 mode QDII)?  This will show which software will 
work with a higher resolution and which ones won't.  I see 8bit and maybe 
24bit color support be added in a second phase.

Geoff

 > Dear All,

 > As my SecondSight... (is still under repair at Henry Courbis' home and
 > I understood he is a busy man which would explain why I have no news
 > from him, I just hope he is going well)

 > ...I was reading the SecondSight documentation about shadowing, the process 
 > which reads the Apple II bus and whenever some data is copied
 > onto a TEXT/GR/HGR/SHR page (A), it is "shadowed" on the VGA board
 > memory and then displayed.

 > I was wondering whether that process was hardware related or software 
 > related. I mean, if one succeeds in writing a 8-bit QuickDraw II (and
 > all of its numerous patches on other tool sets), will that be possible
 > to allocate IIgs RAM for a 8-bit display (one bank for a 320*200
 > screen, 4 for a 640*400 one) and let the SecondSight know where the
 > pseudo new SHR screen is located in memory, so that it would perform
 > its shadowing process from there and not from (A) ?

 > Another means would be to write a Z80 version of QuickDraw but that is 
 > another job!

 > Antoine