Re: Commodore 8296GD

From: Michał Pleban <>
Date: Fri, 05 Oct 2012 16:28:35 +0200
Message-ID: <>

Steve Gray wrote:

> Thanks for testing! That's good to hear that the basic extensions/tokens
> are the same. Of course, I only had the 512 x 256 pixel version at the
> time when I did that. I now have a 512x512 version as well.

Now that's strange, because demo #3 is written for 512x512 ;-)

> One of the neat things about the HSG board is the ability to re-define
> the screen co-ordinate system, so theoretically the software should work
> on either if written properly.

It will not, because you are using IPLOT in your demos which use
absolute coordinates :-P

> Ya, since there is NO access to the display ram, the image viewer is
> EXTREMELY slow. If you look at the code there's like 3 commands to draw
> each pixel. It does take about 20 minutes for the complete screen.
> Sadly there is no pixel PLOT or PSET command. I didn't spend a lot of
> time on the Etch-a-sketch ;-)

Yes, I noticed :-) For my image viewer, I used a simple "compression"
scheme where the software tries to draw as long vertical lines as
possible. So if there is a long row of pixels on a line, it is converted
to a single IPLOT command (and vice versa for black pixels). It works
very well for simple images (like the Commodore logo), it is hovewer
still an overkill for dithered photos or dot patterns (like the
Macintosh desktop picture).

> I tried disassembling the ROM to see if there was a way to access the
> memory somehow but couldn't find anything, although I never completely
> understood the code (not enough time).

There should be a way to access it (at least to read it) because there
is a command to print the screen in an IEEE printer. It must be in the
ROM somewhere :-)

Now with HRE it will be much easier, the pixel data is at $A000 so you
just need to write a small routine to access it (ROM must be banked out
and so the interrupts must be disabled).

Which brings a question - do you possibly have PNG or BMP versions of
the images you are using in your demos? I would like to display them on
the screen, do a memory dump of the bitmap and compare - this would tell
me everything about how the bitmap is organized in RAM.


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Received on 2012-10-05 15:00:05

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