Re: Lo-res/Double lo-res (was: Wacky Game idea)

[John Le Febvre <John@klatch.demon.co.uk>]

In article: <4kk9se$b10@pith.uoregon.edu>  nparker@cie-2.uoregon.edu (Neil Parker) writes:
[SNIP]
> >Talking of double lo-res graphics, how well supported is that mode?  I 
> >know the //c had routines for it in ROM, but does the IIgs?
> 
> Yes, it's there in the IIGS too.  The machine-language entry points have
> never been officially published, but it works quite well from BASIC.  You
> can turn it on like this:
> 
>      10 D$ =  CHR$ (4)
>      20  PRINT D$;"PR#3": PRINT  CHR$ (12)
>      30  POKE 49246,0
>      40  GR

Aaah, I wondered about that.  Is it the CHR$(12) that 'activates' double
lo-res sensing?

[snip]
> I've never investigated it, but I remember reading somewhere that there's
> a bug in the double lores SCRN function.

There's also a bug in the PLOT function.  According to my Merlin ROM 
disassemblies (Merlin-8, //c ROM listings), the bug is that the vertical
coord is not checked correctly and you can PLOT past the 48 point limit,
directly into memory beyond the text screen.

I don't remember noticing the SCRN bug.

If this 'Wacky Game Idea' goes any further, how about using de-bugged
double lo-res routines for the project?  It could even have auto support
for DLR mode on a suitable //e, //c or IIGS... :)
-- 
John.
john@klatch.demon.co.uk