Re: double lowres funkiness

[Dennis Jenkins <dennis@uranium.usb.com>]

David Empson <dempson@actrix.gen.nz> wrote:
> Dennis Jenkins <dennis@uranium.usb.com> wrote:

>>       Anyway, does anyone know why the IIe card and IIgs would implement
>> double lowres graphics differently?  Mr. Empson? :)

> I hardly ever used double lo-res, but I don't remember it behaving oddly
> on the IIgs.  I probably never used it by poking data directly into
> screen memory.

> Have you tried using Applesoft's built-in support (on the IIgs only) for
> double lo-res graphics?  Does it exhibit strange colour effects?  If
> not, is it modifying the values written into main memory to compensate
> for the behaviour you observed?

I thought I talked about this in my original post.  It appears that 
applesoft basic is compensating for what I have discovered.  Odd numbered 
columns (MAIN memory) use a different palette than even numbered columns.  
If I go into double low res and do:

color=1:plot 0,0:plot 1,0:plot2,0:plot3,0
call-151
00/400.401
01/400.401
I see different data in MAIN, but AUX looks correct.


> Have you checked the behaviour on the composite output?  The behaviour
> you observe might be a design fault in the VGC.

It occurs in both composite and RGB.  I truley think this is not a bug in 
the hardware, that it is supposed to be this way.  Otherwise, why would 
applesoft basic implement the hack that I had to in my own code?

> I can't easily test any of this myself, as I don't have a IIgs system
> set up any more.

The main points of my post were:

1) did anyone know about this already?
2) why is the IIe card different from the IIgs?
3) what about other systems (real)?
4) do the emulators do it correctly?